let. - vol. 46 C200QD št. - no. B STROJNIŠKI VESTIMIK 1= JOURNAL OF MECHANICAL ENGINEERING strani - pages 493 - 590 ISSN 0039-24B0 . Stroj V . STJVAX cena BOO SIT SITHDK--4 Mednarodni kongres SITHOK< - 4 Ml^*iiT—iVaifFI—^'"^IliCT^lIrJKiMilllll11 **.....^*"1 "F i ZA TRETJE TISOČLETJE HEATING AND AIR-CONDITIQNI FOR THE THIRD MILLENNIUM Maribor 6. - 8.5.2000 Organizatorji: Organisers: Mednarodni inštitut za hlajenje International Institute of Refrigenatior V/iifVW^ Univ ribor niiiui.iiiiinhl.i.ii .o .o -co .•* :CM ¦~cx> :co -o ¦o :r^-:f-- ).].|'l'1'1'iM • | • Wl'1'lf'l'l'l © Strojni{ki vestnik 46(2000)8,493 © Journal of Mechanical Engineering 46(2000)8,493 Mese~nik Published monthly ISSN 0039-2480 ISSN 0039-2480 Vsebina Contents Strojni{ki vestnik - Journal of Mechanical Engineering letnik - volume 46, (2000), {tevilka - number 8 Razprave Papers Prek, M., Novak, P.: Analitična določitev srednje Prek, M., Novak, P.: An Analytical Determination sevalne temperature zapletene geometrijske of the Mean Radiant Temperature for a Com- oblike prostora 494 plex Room Geometry Stritih, U., Muhič, S., Novak, P: A Computer analiza ogrevalnih in hladilnih obremenitev za Analysis of Heating and Cooling Loads for različne tipe stavb 503 Different Types of Building Pristovnik, A., Črepinšek Lipuš, L., Krope, J.: Preprečevanje izločanja vodnega kamna na Preventation of Surface Precipitation on Heat površinah prenosnikov toplote z uporabo Exchangers Using a magnetic Water-Treatment naprave za magnetno obdelavo vode 509 Device eksergijskih tokov absorpcijske hladilne naprave 517 of Exergy Floes in an Absorption Chiller Krope, A., Krope, J., Tičar, I.: Zmanjšanje tlačnih izgub v vročevodnih cevnih mrežah 525 Friction Losses in District-Heating Pipelines Pristovnik, A., Črepinšek Lipuš, L., Krope, J.: Spremenjeno kristaljenje vodnega kamna pri Modified Scale Crystallization in Magnetic magnetno obdelavi vode 532 Water Treatment obratovalnega hrupa in vibracij okrova radialne Operating Noise and Casing-Vibration Analy- črpalke 538 ses Noeres, P., Holder, D., Althaus, W.: Kombinirano daljinsko ogrevanje in hlajenje v mestu Gera trict Heating and Cooling Network in City of Gera (Nemčija) s tehnologijo parnih kotlov 549 (Germany) Using Steam-Jet Ejector Technology Poredoš, A.: Energetska učinkovitost daljinskega hlajenja za klimatizacijo prostorov 557 Cooling for Space Conditioning Remec, J., Arhar, A.: The Possibilities of Reduc- perature toplotnega vira z absorpcijskimi ing the Temperatures of the Heat Source for hladilnimi napravami 564 Absorption Chillers Goričanec, D., Krope, J., Tičar, I.: Določitev Goričanec, D., Krope, J., Tičar, I.: The Determina- optimalne debeline izolacije cevnih sistemov za tion of the Optimum Insulation Thickness of transport hladilnega sredstva 573 Pipe Systems for Transporting Cooling Media Taccani, R.: Kogeneracija z gorilnimi celicami v Taccani, R.: Residential Co-Generation Using Fuel stanovanjskih poslopjih 580 Cells Navodila avtorjem 589 Instructions for Authors stran 493 glTMDDC © Strojni{ki vestnik 46(2000)8,494-502 © Journal of Mechanical Engineering 46(2000)8,494-502 ISSN 0039-2480 ISSN 0039-2480 UDK 536.3:536.2:697.97 UDC 536.3:536.2:697.97 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Analiti~na dolo~itev srednje sevalne temperature zapletene geometrijske oblike prostora An Analytical Determination of the Mean Radiant Temperature for a Complex Room Geometry Matja` Prek - Peter Novak Sevalne toplotne izgube pomenijo sestavni del toplotnega ravnotežja človeka v prostoru. Pravilna določitev deleža sevalnega toplotnega toka je potrebna za oceno vpliva tega parametra na toplotno ugodje. Toplotno ravnotežje je odvisno predvsem od površinskih temperatur in kotnega faktorja med človekom in površinami prostora. Ker so notranje površine sestavljene iz različnih elementov, je izračun kotnega faktorja zahteven. V tem primeru pomeni računalniški program primerno orodje za izračun sevalnih toplotnih tokov, predvsem za zapleteno sestavljene površine, kakršne so v dejanskih razmerah. Predstavljeni algoritem temelji na izračunu kotnih faktorjev, pri čemer je upoštevan zakon seštevnosti. Postopek izračuna omogoča določitev kotnih faktorjev za sestavljene površine in s tem upoštevanje zapletenega vpliva kotnih faktorjev na sevalni toplotni tok, kakršen je npr. pri sedeči osebi in znani usmeritvi. Matrično zasnovan postopek omogoča določitev vpliva različnih parametrov na srednjo sevalno temperaturo. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: ugodje bivalno, prenos toplote, sevanje, temperature sevanja) Radiative heat losses represent a substantial part of the total heat balance of the human body in a closed space. The correct determination of this contribution is necessary in order to gain an insight into the influence of this parameter on human thermal comfort. The thermal balance is strongly affected by surface temperatures and by the angle factor between a body and a wall surface. Since a room’s internal surfaces are composed of various parts, the calculation of view factors becomes more complex. Therefore, a computer algorithm is a useful tool for determining the radiant heat exchange, particularly for the complex surface compositions encountered in practical situations. The proposed algorithm is based on the computation of view factors, which are additive. This algorithm enables the computation of view factors for composite surfaces, thus allowing for the complex impact of view factors on thermal radiative heat exchange, as is the case for the seated posture and other orientations of the human body. The matrix-based approach makes it possible to determine the influence of various parameters on the mean radiant temperature. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: thermal comfort, heat transfer, radiation, radiant temperature) 0 UVOD Toplotno ugodje ljudi je odločilen dejavnik, ki določa kakovost bivalnega okolja v stavbah. Zagotovljeno je z vzdrževanjem vplivnih parametrov v predpisanih mejah ob hkratni izravnavi vseh motečih vplivov. Analiza sevalnega ogrevalnega sistema pokaže, da je pri zagotavljanju kakovosti bivalnega okolja odločilna razlika med temperaturo zraka v prostoru in dejansko temperaturo. Upoštevajoč toplotno ugodje imajo ljudje subjektivno nagnjenost k toplejšim obodnim 0 INTRODUCTION The thermal comfort of people in confined environments is a crucial issue for the proper assessment of the indoor quality of buildings. It should be considered both as a requisite by itself and as a fundamental preliminary requirement for establishing other indoor needs. Thermal comfort is ensured by maintaining the declared values of the factors determining thermal comfort constant, while eliminating any disturbing influences causing local thermal discomfort. When analysing a radiant heating system, the most pronounced factor is VH^tTPsDDIK stran 494 M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination stenam in hladnejšemu zraku; zato je primerna natančnejša določitev sevalnega dela prenosa toplote. Toplotno ravnotežje človeka je odvisno od sevalnega toplotnega toka med telesom in obodnimi stenami, ta pa je odvisen od površinskih temperatur in kota, katerega tvorita telo in opazovana površina. Za določitev toplotnega ugodja ali neugodja je zato treba najprej določiti kotne faktorje obodnih površin glede na položaj človeka. Za preproste površine so algoritmi za izračun kotnih faktorjev že določeni. Vendar so v resničnem stanju površine sestavljene iz različnih neizotermnih elementov, ki onemogočajo neposredno uporabo algoritmov. Kot primer preprosto sestavljene neizotermne notranje površine so različni elementi, npr. stene, okna, vrata in ogrevala. Zaradi tega postane izračun kotnih faktorjev zelo zapleten in je potrebno dosledno upoštevanje temperaturnih karakteristik površin. Zato je vpeljan algoritem, ki omogoča izračun projekcijskega faktorja človeka glede na dano stanje. Poprej je bila razvita metoda za izračun kotnega faktorja, ki temelji na neposrednem izračunu projekcijskega faktorja. Kotni faktorji so podani kot približki rešitev sistema enačb in so predstavljeni v obliki zbirke diagramov. V teh diagramih je kotni faktor podan neposredno kot funkcija brezdimenzijskega geometrijskega parametra. Enačbe so rešene za šest značilnih smeri (površin prostora), ki predstavljajo značilni prostor. Za te primere je predpostavljena razdelitev površin kvadra na podpovršine; zaradi simetrije človeškega telesa se število kotnih faktorjev zmanjša in so odvisni od usmeritve med človekom in delno površino. Za tipični prostor se število kotnih faktorjev zmanjša na šest za sedečega človeka, tri za stoječega in dva za primer neznane usmeritve. Naslednji korak k poenostavitvi in s tem bolj uporabni obliki zapisa kotnih faktorjev je dobljen z metodo najmanjših kvadratov. Pri tem so kotni faktorji podani v obliki eksponentnih enačb v funkcijski odvisnosti od brezdimenzijskih geometrijskih parametrov. Ta poenostavljena metoda izračuna kotnih faktorjev zagotavlja dobro ujemanje izračunanih vrednosti z eksperimentalno izmerjenimi vrednostmi pa tudi z rešitvami sistema enačb. Način zapisa kotnih faktorjev skupaj s parametri omogoča preprosto uporabo računalniškega programa. Pri računanju resničnih stanj so obodne površine razdeljene na štiri površine kvadra (glede na položaj in usmeritev človeka) in z upoštevanjem zakona seštevnosti določen kotni faktor za celotno površino. Posplošen algoritem omogoča izračun kotnih faktorjev za poljubne neizotermne elemente obodnih površin prostora. the difference between the indoor air temperature and the effective temperature. Regarding personal comfort, the human occupant has a subjective preference for a warmer building structure and cooler indoor air, indicating that radiative heat exchange should be favoured. The human body’s thermal balance is strongly affected by radiative heat exchanges with surrounding surfaces, which are a function of the surface temperatures and the angle at which the human body senses them. This means that in order to establish local thermal comfort or discomfort, view factors of people with respect to the envelope surfaces must first be assessed. Algorithms for computing these view factors for simple plane surfaces have already been determined. However, in practical cases, the room’s internal surfaces are composed of various parts, each possessing a specific thermal situation. The complex internal surface of a room composed of a wall, a window, a door and a heating panel would be an example of this kind of mixture of composite plane surfaces. In this case, the calculation of view factors becomes much more complex and requires a careful management of the thermal and geometric properties of the surfaces. A comprehensive algorithm is introduced here which allows for the computation of angle factors of people with respect to the given complex situations. In a previous study, a method of calculating the view factor was determined which avoids the direct calculation of the projected area factor. In this work, the view factors were given as solutions of equations and presented in the form of sets of graphs. In these graphs, the view factor was directly presented as a function of dimensionless geometrical parameters. The equations were solved for six relevant cases (room walls) that occur in a typical room. A division of parallel-piped surfaces into sub-surfaces has been proposed for these cases. Due to the symmetry of the human body, the number of view factors is reduced and the view factors are dependent on the orientation of the person and sub-surface. The number of view factors for the typical sub-surfaces of an enclosure is reduced to six for a seated person, three for a standing person and two when the orientation of a person is unknown. Another step toward simplification, and thus to a more useful form of view factors, was suggested by the observation of graphs. There the view factors are given in the form of exponential equations dependent on dimensionless geometrical parameters. This simplified method for calculating the view factors enables good agreement between the calculated and actual values determined by solutions of equations and experimental data. The form of the view factors, along with the determined parameters, allows them to be used in computer algorithms. For practical applications, the surrounding surfaces should be divided into four rectangular sub-surfaces (with respect to the human body’s position and orientation) and, by means of the additive property, computed to determine the whole view factor. This general algorithm could also be used for computing the view factor for non-isothermal elements of the wall. | gfin=i(gurMini5nLn 00-8_____ stran 495 I^BSSIfTMlGC M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination 1 KOTNI FAKTOR MEDČLOVEKOM IN POVRŠINO PROSTORA Kotni faktor med človekom in pravokotno izotermno površino i? lahko izračunamo po enačbi, podani v [1] in standardu [2]: x a z b 1 ANGLE FACTOR BETWEEN THE HUMAN BODY AND THE ROOM SURFACE As presented in the work of Fanger [1] and determined with a standard [2], the angle factor between the human body and a rectangular surface F can be computed as: P____ y 0 y 0 1 + lxl2 +fz'2 d\-)d(-) (1) kjer sta a in b širina in višina izotermne površine A ter fP projekcijski faktor. Pri praktični uporabi enačbe (1) se pojavita dva problema: določitev projekcijskega faktorja f in vpliv neizotermne sestavljene površine. Zato je bila razvita metoda, ki ne temelji na neposrednem računanju kotnih faktorjev. V [1] so podani kot rešitve enačb, prikazane v obliki zbirke diagramov. V njih je kotni faktor podan neposredno kot funkcija brezdimenzijskih parametrov a/b in b/c. Enačbe so rešene za šest značilnih primerov (sten prostora). Izračun temelji na delitvi površine kvadra na štiri delne površine. Zaradi simetrije človeka se število kotnih faktorjev zmanjša in so odvisni od usmeritve človeka glede na delno površino. Za površine kvadra se število kotnih faktorjev zmanjša na šest za sedeč položaj, tri za stoječ in dva za primer neznane usmeritve. Naslednji korak k poenostavitvi in s tem uporabnejši metodi določitve kotnih faktorjev je predlagan v [3]. Na temelju grafično predstavljenih rešitev enačb je narejena analiza s postopkom najmanjših kvadratov, s katero je dobljena eksponentna enačba kot funkcija brez-dimenzijskih parametrov a/c in b/c: where a and b are the width and height of the isothermal surface A, and fP is the projected area factor. However, two problems arise in the practical application of equation (1): the determination of the projected area factor fP and the influence of the non-isothermal composite surface. In order to calculate the view factor, a method which avoids the direct calculation of the projected area factor has been established. In the previous work of Fanger [ 1 ], the view factors are determined as solutions of equations and presented in the form of sets of graphs. In these graphs, the view factor is directly presented as a function of the dimensionless geometrical parameters a/c and b/ c. Equations are solved for six relevant cases (room surfaces) that occur in a typical room. For this, a division of the parallelepiped surfaces into sub-surfaces is proposed. Due to the symmetry of the human body, the number of view factors is reduced and is dependent on the orientation of the person to the sub-surface. The number of view factors for typical sub-surfaces of an enclosure is reduced to six for a seated person, three for a standing person and two for person with unknown orientation. Another step toward simplification, and thus to a more useful form of view factors, was made by Rizzo et al. [3]. As suggested by the observation of graphs, the view factors are given in the form of exponential equations dependent on geometrical parameters, the dimensionless parameters a/c and b/c in the following equation: F = F P->A sat,max kjer sta in 1-exp t = A + B g = C + D 1-exp — (2) F ak pomeni največjo vrednost projekcijskega faktorja za dano podpovršino v odvisnosti od usmeritve (znana ali neznana) in položaja človeka (sedeč ali stoječ). Koeficienti A, B, C, D in E so določeni z linearno regresijo za parameter t in večkratno aproksimacijo za parameter g. Primerjava rezultatov, dobljenih s to metodo, z rezultati rešitev enačb in izmerjenih vrednosti, je dokazala where a ~c and - + E--cc F represents the maximum saturation value for a given sub-surface depending on human body orientation (known or unknown) and posture (seated or standing). The parameters A, B, C, D and E are determined by simple linear regression for the parameter t and by multiple linear regression for the parameter g. As shown by Nucara et al. [4], this simplified method for calculating the view factors enables good agreement between the VBgfFMK stran 496 f M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination upravičenost uporabe poenostavljene metode izračuna [4]. Oblika enačbe (2) omogoča preprosto uporabo koeficientov v računalniškem programu. Za reševanje dejanskih primerov je potrebna samo delitev obodnih površin na štiri delne površine (glede na usmeritev in položaj človeka), kotni faktor za celotno površino pa je določen z zakonom o seštevnosti. 2 VPLIV SESTAVLJENIH POVRŠIN Na sliki 1 je prikazan najpreprostejši primer enostavne izotermne površine. Če normala na površino A poteka skozi točko P (opazovana točka v prostoru, t. i. osrednja točka) in se ujema z ogliščem površine, potem lahko določimo kotni faktor z enačbo (2) v odvisnosti od usmeritve in položaja človeka. V primeru, da se normala ne ujema z ogliščem, kakor je prikazano na sliki (1), potem lahko določimo kotni faktor ob upoštevanju seštevnosti z enačbo (3): calculated and actual values determined from solutions of equations, as well as experimental data. The form of equation (2) along with the determined parameters enables their use in computer algorithms. For practical applications, the surrounding surfaces should be divided into four rectangular sub-surfaces (with respect to the human body’s position and orientation) and by means of the additive property computed for the whole view factor. 2 THE INFLUENCE OF COMPOSITE ROOM SURFACES The simplest example of an isothermal room surface is shown in Figure 1. If the normal from the subject P (the so-called generic point) coincides with the corner point of surface A, the view factor can be directly computed with equation (3) depending on the human body orientation and posture. In addition, if the normal does not coincide with the corner point (as shown in Figure 1), then the view factor can be determined by the application of the additive property in the following way: ali F = F + F + F + F P^A P->1 P^2 P^3 P^4 or 4 p->a = =1 P->i (3) kjer i-ta površina pomeni delno površino abi. Enačbo (3) lahko uporabimo kot splošni algoritem za izračun kotnega faktorja za poljuben element površine. Z delitvijo površine, pri čemer element A že pomeni delni element stene, na naslednje štiri delne elemente (na sl. 2. delni elementi 1, 2, 3, 4), lahko izračunamo kotni faktor za vsako delno površino z enačbo (3). S ponovitvijo postopka za vse obodne površine prostora (ki so sestavljene iz različnih elementov) in za vse položaje človeka lahko določimo skupni kotni faktor. where surface i represents sub-surface aibi. Equation (3) can be used as a general algorithm for calculating the view factor for an arbitrary element of the wall. By division of the surface, where element A of the wall represents the sub-surface, into four sub-surfaces (1, 2, 3, 4), the view factor can then be determined by solving equation (3) for every subsurface. By repeating this procedure for all room walls (composed of different elements) and for all positions of the person in the room, the total view factor can be estimated. Sl. 1. Kotni faktor med osrednjo točko P in površino A (z izmerami a x b) Fig. 1. View factor between generic point P and surface A (dimensions a x b) M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination Enačba (3) velja le v primeru, če se normala med točko in površino ujema z ogliščem površine kvadra (pogoj za uporabo eksperimentalno določenih kotnih faktorjev). Vendar lahko v vsakem primeru določimo normalo na ravnino, v kateri je opazovana površina tako, da se ujema s točko P. Kotni faktor površine določimo z delitvijo ravnine na štiri delne površine, od katerih je ena opazovana površina. V običajnem primeru, ko je zid sestavljen iz elementov z različnimi površinskimi temperaturami (npr. okno, ogrevalo), lahko določimo kotni faktor za posamezni element po opisanem postopku. Štiri delne površine oblikujemo tako, da se normala skozi opazovano točko ujema z ogliščem površine na ravnini elementa; preostala oglišča delnih površin so določena z oglišči elementa. Na sliki 2 je prikazanih nekaj možnih razporeditev. Equation (3) functions only if the normal from the subject coincides with the common corner point of the rectangles (a condition for using the experimentally determined view factors). Nevertheless, in the case of isothermal sub-surfaces with equal temperature, we are able to sweep the normal from the surface in such a way, that it coincides with the normal from the subject. The view factor for an arbitrary human position in the room can be determined by splitting the surface into four sub-surfaces and applying the additive property. This general algorithm can also be used for computing the view factor for non-isothermal elements of the wall. In the usual case, where the wall is composed of elements with different temperatures (e.g. windows, heating panels), the view factor can be determined in a similar way to the sub-surface. The four sub-surfaces are constructed in such a way that the normal from the subject represents one corner of the surface; other corners and the middle point of the sub-surfaces are determined by corners of the element. Some possible arrangements are shown in Figure 2. Sl. 2. Primeri geometrijskih pogojev za izračun kotnega faktorja za osrednjo točko P Fig. 2. Examples of geometrical conditions for calculating the view factor for generic point P Kotni faktor je določen z enačbo (3) z The view factor is then determined using upoštevanjem seštevnosti: equation (3) by means of the additive property in the following way: za primer na sl. 2a: for the case in Figure 2a: Fp^a Fp->(1+ 2+3+4) Fp->(1+4) Fp->(3+4) p->4 za primer na sl. 2b: za primer na sl. 2c: for the case in Figure 2b: Fp->a Fp_>(1+2+3+4) p->1 Fp->4 for the case in Figure 2c: (4a) (4b) (4c). Da lahko uporabimo računalniški program In order to create a computer algorithm for za izračun kotnih faktorjev za celotni tloris prostora, calculating the view factor for an entire floor plan, moramo ustrezno definirati koordinatni sistem. Delitev attention must be paid to the proper determination of površine elementa ali ravnine na delne površine in the coordinate system. The division of the surface upoštevanje zakona seštevnosti zahteva pravilno into four sub-surfaces and an application of the ad- Fp->a Fp->(1+2+3+4) p->3 Fp->4 grin^(afcflM]SCLD ^BSfiTTMlliC | stran 498 M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination določitev predznaka za posamezno delno površino. Glede na postopno razvrstitev delnih površin, kakor je prikazana na slikah 2a, b in c, ter določitev kotnega faktorja z enačbami (4a, b in c), lahko algoritem posplošimo: ditive property requires the determination of the sign for certain sub-surfaces. According to the arrangements shown in Figures 2a, b, c and the equations (4) for computing the relevant view factor, one can deduce a general algorithm: FP 4 ¦sign(ai-bi) (5). Ko določimo kotne faktorje za posamezne elemente, lahko izračunamo kotni faktor za sestavljeno površino z enačbo: When the view factors for individual subsurfaces are determined, the view factor for the composed wall can be expressed as: tena| usmeritev all| orientation F P .celotna p total surface| orientatio Tfp ter povprečno sevalno temperaturo T za znano usmeritev v prostoru: delna povrsina| usmeritev sub-surface| orientation (6) and the mean radiant temperature Tmrt for a given orientation in the room is then: N IFP (7), kjer je Ti absolutna površinska temperatura i-te notranje površine in FP-> kotni faktor med človekom (osrednjo točko v prostoru) in i-to površino (ali podpovršino). 3 PRIMER Uporabnost predstavljenega postopka je prikazana na primeru izračuna povprečne sevalne temperature za zid, sestavljen iz različnih elementov. Na sliki 3 je primer preproste zunanje stene, sestavljene iz vrat, okna in ogrevala (radiatorja). V preglednici 1 so podane geometrijske in temperaturne predpostavke za posamezne površine. Zaradi preglednosti je pri računanju sevalne temperature upoštevana samo ena stena. Ker algoritem temelji na uporabi enačbe (2), so potrebni geometrijski parametri določeni avtomatično z definicijo elementov stene (ali prostora), razen višine osrednje točke, ki je definirana s predpostavljenim položajem človeka. Na ta način so izbrani koeficienti enačbe (2), ki so določeni glede na položaj človeka in s tem posredno odvisni od geometrijske oblike prostora in elementov. where Ti is the absolute temperature of the i-th inter-nal surface and FP->i is the view factor between the person (generic point in room) and i-th surface (or sub-surface). 3 CASE STUDY The potential use of the introduced algorithm can easily be shown by means of an application aimed at the calculation of the mean radiant temperature for a wall which is composed of different elements. In Figure 3, an example of a wall composed of a door, window and heating panel is shown. Table 1 contains the geometric and thermal assumptions for the wall surfaces; for the sake of clarity, the influence of only one wall on mean radiant temperature is analysed. Since the algorithm is based on the use of equation (2), the required geometrical parameters are automatically defined by given wall (or room) elements, except for the height of a generic point which is determined by the proposed body posture. The parameters used in equation (2) are defined by the body posture and, thus, are chosen depending on the geometry of the room and its elements. Sl. 3. Primer predpostavljene sestave zunanje stene Fig. 3. Assumed composition of the wall in this case stran 499 glTMDDC M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination Preglednica 1. Parametri stenskih površin Table 1. Parameters of the wall surfaces element stena wall vrata door okno window ogrevalo heating panel dolžina length m 5 3 1 2 višina height 2 1 1 0,8 površinska temperatura surface temperature oC 18 16 14 50 Na naslednjih slikah so prikazani izračunani kotni faktorji stene ter povprečna sevalna temperatura. Ker je algoritem splošen, ga lahko uporabimo za različne sestavljene površine, npr: - poljubno lego elementa stene ali - geometrijsko obliko elementa ali - površinsko temperaturo. In the following figures, the calculated view factors and mean radiant temperatures are presented. In these examples, the height of the generic point is used as a variable. Since the algorithm possesses a general structure, it is easily applied to different surface compositions, such as: - the position of the element within the wall, - the arbitrary geometry of the element, - the surface temperature of the element. o0,4 C 0,3 t 0,2, 20 širina 30 width dm 30 20 dolžina length 10 0,4 F 0,3 R^ P 0,2 0,1' 40 dm šir 2 n 0 a 30 width dm 30 20 dolžina length 40 dm za sten Fig. 4. Calculated view factor for wall (left) and door (right) 0,04 0,03 0 02, 0,01! 20 širina 30 width 40 dm dm 30 20 dolžina length 0,4 F 0,3 r^p 0 2 0,1' 20 širina width dm 30 20 dolžina length evo) in ogrevalo (desno) ow (left) and heating panel (right) VH^tTPsDDIK stran 500 M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination °C 20' t 1 1 5cl mrt 0 10 20 širina 30 width 40 dm 30 20 dolžina 10 length tmrt 4 2\ dm 20 širina 30 width 40 dm 30 20 dolžina 10 length dm S višine Fig. 6. Calculated mean radiant temperature t for different heights: 0.6 m above the floor (left) and 1.2 m mrt (right) 4 SKLEPI Prikazana metoda predstavlja analitični postopek k določitvi optimalnega toplotnega okolja v stavbah. Predlagani algoritem temelji na izračunu kotnih faktorjev ob upoštevanju zakona seštevnosti. S tem je omogočen izračun povprečne sevalne temperature za sestavljene površine ob hkratnem upoštevanju zapletenega vpliva usmerjenosti človeka v prostoru. Zaradi matričnega načina izračuna je mogoča analiza vpliva različnih parametrov tako na povprečno sevalno temperaturo kakor tudi na pričakovano toplotno ugodje oz. neugodje. Hkrati je mogoče tudi upoštevanje drugih parametrov (temperaturni gradient, relativna hitrost zraka itn.), ki vplivajo na toplotno ugodje in so izraženi kot vrednost pričakovane povprečne presoje (PVM). Za zagotovitev najboljših toplotnih razmer mora biti doseženo ravnotežje med toplotnimi viri in ponori. Metoda omogoča določitev vpliva karakteristik toplotnega vira - ogrevala (temperatura, geometrijska oblika) na povprečno sevalno temperaturo, ki predstavlja del toplotnega okolja. Za boljšo predstavljivost so lahko rezultati izračuna podani v obliki različnih izometričnih diagramov. Ta metoda je učinkovito orodje za natančno določitev medsebojnega vpliva ogrevalnega sistema in gradbene konstrukcije, s čimer lahko dosežemo največje mogoče področje toplotnega ugodja. V idealnem primeru lahko to metodo uporabimo v fazi načrtovanja objekta in s tem določimo najboljše možno razmerje med toplotno-tehničnimi lastnostmi stavbe in ogrevalnega sistema. 4 CONCLUSIONS The thermal comfort of people in confined environments is a crucial issue for the proper assessment of the indoor quality of buildings. The method presented in this paper represents an analytical tool for determining the optimum thermal environment for people in buildings. The proposed algorithm is based on the computation of view factors using the additive property. This algorithm enables the calculation of mean radiant temperature for composite room surfaces, even allowing for the complex impact of body posture. The matrix-based approach allows us to determine the effect of various parameters on mean radiant temperature, as well as on thermal comfort or discomfort. This approach also enables the consideration of other parameters (air temperature gradient, air velocity etc.) whose impact on thermal sensation is expressed as the predicted mean vote (PMV) value. In order to achieve optimum thermal conditions, the thermal balance between heat sources and sinks must be established. This method enables the determination of the influence of heating source characteristics (temperature, geometrical parameters) on mean radiant temperature as a part of the overall environmental conditions. A graphical rendering of an isometric map is used for better visual interpretation of the results. This method presents a useful tool for determining the correct interplay between heating system and building structure, thus achieving the maximum possible thermal comfort area. This method could, ideally, be incorporated into the architectural planning phase of buildings in order to determine the best relationship between the the building’s structure and its heating system. gfin^OtJJlMISCSD 00-8 stran 501 |^BSSITIMIGC M. Prek - P. Novak: Analiti~na dolo~itev - An Analytical Determination [1] [2] [3] [4] 5 LITERATURA 5 REFERENCES Fanger, P.O. (1970) Thermal comfort, Danish Technical Press. ISO 7729 (1994) Thermal environments - Instruments and methods for measuring physical quantities. Rizzo, G., G. Cannistraro, G. Franzitta, C. Giaconia (1992) Algorithms for the calculation of the view factors between human body and rectangular surfaces in parallelepiped environments. Energy and Buildings, Vol. 19 (1), 51-60. Nucara, A., M. Pietrafesa, G. Rizzo, G. Rodono (1999) Human body view factors for composite plane surfaces. Proceedings Indoor-Air 99, Edinburgh, Scotland, 650-655. Naslov avtorjev: dr. Matjaž Prek prof.dr. Peter Novak Fakulteta za strojništvo Univerze v Ljubljani Aškerčeva 6 1000 Ljubljana Authors’ Address: Dr. Matjaž Prek Prof.Dr. Peter Novak Faculty of Mechanical Engineering University of Ljubljana Aškerčeva 6 1000 Ljubljana, Slovenia Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 VBgfFMK stran 502 © Strojni{ki vestnik 46(2000)8,503-508 © Journal of Mechanical Engineering 46(2000)8,503-508 ISSN 0039-2480 ISSN 0039-2480 UDK 697.97:519.682:628.83 UDC 697.97:519.682:628.83 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Ra~unalni{ka analiza ogrevalnih in hladilnih obremenitev za razli~ne tipe stavb A Computer Analysis of Heating and Cooling Loads for Different Types of Building Uro{ Stritih - Simon Muhi~ - Peter Novak Prispevek prikazuje simulacije ogrevalnih in hladilnih obremenitev za različne tipe stavb s programskim paketom TRNSYS. Prikazujemo sedem različnih tipov stavb in štiri različne klimatske pogoje v Evropski zvezi. Skupaj je narejenih 28 simulacij, v tem prispevku pa prikazujemo rezultate za pisarniško zgradbo. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: zgradbe pisarniške, energija toplotna, simuliranje obremenitev, analize računalniške) This paper presents simulations of heating and cooling loads for different types of building with the TRNSYS programme package. We present seven different building types and four different weather conditions in the European Union. Altogether we made 28 simulations and the results for an office building are shown in this paper. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: office buildings, thermal energy, load simulation, computer analysis) 0 UVOD Toplotne in hladilne obremenitve so toplotna energija, ki jo moramo dovesti ali odvesti iz notranjosti prostora stavbe, da ohranimo karakteristike ugodja. Ko obremenitve določimo, se je treba lotiti določevanja opreme za ogrevanje in hlajenje. Najpomembnejša skrb inženirjev je določiti največjo obremenitev, ker je od te odvisna moč opreme. Le-ta se ujema z ekstremnimi vrednostmi vročega ali hladnega vremena, ki jih imenujemo projektni pogoji. Naftna kriza je izostrila našo zavest do energije in računalniška revolucija je dala opremo za optimiranje projektiranja stavb in za izračun stroškov energije. Svež zrak v stavbi je pomemben za ugodje in zdravje. Energija za pripravo tega zraka je pomemben dejavnik. Premalo zraka povzroča sindrom bolne stavbe, preveč zraka pa povzroča večjo rabo energije. Izmenjava zraka je misljena kot tok zunanjega zraka, ki prečka mejo poslopja in ga je treba klimatizirati. Pogosto je primerno, da ga delimo s prostornino stavbe, kar izražamo v enotah izmenjav zraka na uro. 1 TRNSYS Za simuliranje smo uporabili računalniški program TRNSYS [1] (‘tran-sys’), ki je komercialno 0 INTRODUCTION Heating and cooling loads are thermal energy that must be supplied or removed from the interior of a building in order to maintain comfortable conditions. Once the loads have been established, one can proceed to the supply side and determine the performance of the required heating and cooling equipment. Of primary concern to engineers are the peak loads, because they determine the capacity of the equipment. They correspond to the extremes of hot and cold weather, and are called design conditions. The oil crises have sharpened our awareness of energy, and the computer revolution has given us the tools to optimise the design of a building and to compute the cost of energy. Fresh air in a building is essential for comfort and health, and the energy for conditioning this air is an important factor. Not enough air, and one risks sick-building syndrome; too much air, and one wastes energy. The supply of fresh air, or air exchange, is stated as the flow rate of the outdoor air that crosses the building boundary and needs to be conditioned. Often it is convenient to divide it by the building volume, expressing it in units of air changes per hour. 1 TRNSYS For the simulation we have used the TRNSYS [1] (‘tran-sis’) computer programme, com- gfin^OtJJlMISCSD 00-8 stran 503 |^BSSITIMIGC U. Stritih - S. Muhi~ - P. Novak: Ra~unalni{ka analiza - A Computer Analysis na voljo od leta 1975 in je namenjen simuliranju prehodnih pojavov toplotnih sistemov. TRNSYS je za reševanje problemov zasnovan modularno in uporablja računalniški jezik Fortran. Na primer podprogram Type 32 vsebuje model hladilne naprave. Podprogram Type 56 vsebuje model večconske zgradbe. Vsak modul ima vhod in izhod. Velikost tokov ter temperature vode in zraka so vstopni podatki za modul Type 32, medtem ko sta celotna in latentna toplotna moč izhodna podatka iz modula. Z izdelavo vhodnega modela uporabnik ukaže TRNSYSu, kako naj poveže module med seboj, ki tako tvorijo sistem. TRNSYS potem kliče posamezne podprograme glede na vhodno datoteko in iterira podatke v vsakem časovnem koraku, dokler sistem enačb ni rešen. Alternativa tej metodi je za raziskovalce, da napišejo enoten program, ki modelira samo en sistem. Toda vsakršne spremembe so pri takem programu bolj zapletene, kakor če uporabljamo TRNSYS. 2 REFERENČNE STAVBE Pri naših simuliranjih smo uporabili naslednje objekte [4]: - pisarno - bolnišnico - hotel - šolo - prodajalno - stanovanjsko poslopje - enodružinsko stavbo Za pisarniški objekt smo uporabili World Trade Center v Ljubljani. Zgradba je usmerjena na sever-jug. Tloris ima izmere 28,35 x 25,6 m. Ima pritličje (4,5 m višine) + eno nadstropje (4,5m) + 15 nadstropij z višino 3,5m. Streha ima strmino 12°. Celotna višina objekta na jugu je 61,5m. Za bolnišnico smo vzeli porodnišnico Univerzitetnega kliničnega centra v Ljubljani. Tloris poslopja je 44 x 38 m. Usmerjena je na sever-jug. Višina poslopja je 24 metrov (pritličje + 5 nadstropij, višina enega nadstropja je 4m). Prostornina poslopja je 44 x 38 x 24 = 40128 m3. Hotel ima tloris 18 x 40 m in prostornino 36000 m3. 100 % je zaseden v poletni in 35% zimski sezoni. Povedali so nam, da je povprečna temperatura v hotelu pozimi 23 °C in poleti 21 °C. Za šolo smo uporabili poslopje s tlorisom 30 x 80 m (okoli 8 razredov v vsakem od dveh nadstropij). Pouk teče (v razredih na levi) samo od 8:00 do 15:00 ure. V njej je 500 učencev in učiteljev. V popoldanskem času so samo dejavnosti v telovadnici (prostor na desni) in je v uporabi do 22:00 ure. Učence jemljemo kot standardne osebe. ^BSfirTMlliC | stran 504 mercially available since 1975, which is designed to simu-late the transient performance of thermal energy systems. TRNSYS relies on a modular approach to solve large systems of equations described by Fortran subroutines. Each Fortran subroutine contains a model for a system component. For example, Subroutine Type 32 contains a model of a cooling coil. Subroutine Type 56 contains a model of a multizone building. Each component has inputs and outputs. The inlet flow rates and temperatures for the air and water are inputs to the Type-32 model, while the total and latent cooling rates are among the outputs of the model. By creating an input file, the user directs TRNSYS to connect the various subroutines to form a system. The TRNSYS engine calls the system components based on the input file and iterates at each timestep until the system of equations is solved. The alternative to this method is for the researcher to write a single, monolithic program that models only the system at hand. Subsequent changes to the system configuration are more difficult with monolithic programs than they are with modular programs such as TRNSYS. 2 REFERENCE BUILDING In our simulations we have taken the following reference buildings [4]: - office - hospital - hotel - school - store - apartment house - single house For the office building we have used the World Trade Centre in Ljubljana. The building has a north-south orientation. The ground plan has dimensions of 28.35 x 25.6 m. It has a ground floor (height 4.5 m) + one floor (4.5m) + 15 levels with a height of 3.5m. The roof has an angle of 12°. The total height of the object to the south is 61.5 m. For the hospital we chose the maternity hospital at University Clinical Centre. The ground plan of the building is 44 x 38 m. It is oriented north-south. The height of the building is 24 meters (ground floor + 5 floors, the height of 1 floor is 4m). The volume of the building is 44 x 38 x 24 = 40128m3. The hotel has a ground plan of 18 x 40 m and a volume of 36000 m3. It has 100 % occupancy in the summer and 35 % in the winter. We were told that the temperature of the hotel in winter is 23 °C and in sum-mer 21°C. For the school we took a building with a ground plan: 30 m x 80 m (cca. 8 classes on each of two floors). The lessons are only in progress (rooms on the left) from 8:00 till 15:00 hrs. There are 500 pupils and teachers. In the afternoon there are some activities only in the gymnasium (room on the right) which is in use till 22:00. The pupils are taken as standard persons. U. Stritih - S. Muhi~ - P. Novak: Ra~unalni{ka analiza - A Computer Analysis Za primer prodajalne smo uporabili supermarket MERCATOR. Nova stavba, ki je bila zgrajena leta 1999, ima tloris 170 m x 110 m z višino 8 m. Daljša fasada je usmerjena na JV-SZ. Prostornina poslopja je V = 170 x 110 x 8 = 149600 m3. Za stanovanjsko poslopje smo uporabili večdružinsko stavbo. Stavba je usmerjena na sever-jug. Tloris meri 16 m x 64 m. Imamo pritličje in 12 nadstropij ter podstrešje. Višina nadstropja je 3 m in stavba je za 270 ljudi. Prostornina je 40960 m3 (224 stanovanjskih enot). Streha je ravna in pohodna. Za enodružinsko hišo smo analizirali hišo za eno družino v ljubljanskem predelu Murgle. Tloris stavbe je 15 x 8 metrov in je usmerjena na sever -jug. 3 KLIMATSKI PODATKI Tipe stavb, predstavljene v 2. poglavju smo simulirali s štirimi klimatskimi pogoji v Evropi. Uporabili smo Testno referenčno leto (TRL - TRY) [2] za naslednje države: - Velika Britanija - London - Švedska - Stockholm - Italija - Rim - Slovenija - Ljubljana Podatki za TRL so sestavljeni iz mesečnih vrednosti različnih let. Za Ljubljano je Testno referenčno leto sestavljeno iz podatkov v letih 1961 do 1980. Testno referenčno leto vsebuje naslednje podatke: 1) Številko dneva v letu (1 do 365), 2) Zunanjo temperaturo (°C) 3) Relativno vlažnost (%) 4) Hitrost vetra (m/s) 5) Globalno sevanje na vodoravno ploskev (kJ/hm2) - če je vrednost nič, potem je podano neposredno sončno sevanje 6) Uro v dnevu 7) Neposredno sončno sevanje (kJ/hm2) - če je vrednost nič, potem je dano globalno sevanje 8) Difuzno sončno sevanje (kJ/hm2) - če je vrednost nič, potem je dano globalno sevanje 4 SIMULIRANJA Simuliranja smo izvajali s programom TRNSYS s podatki za objekte (poglavje 2) in s podatki za testno referenčno leto (poglavje 3). Za vse primere smo vzeli nespremenljiv koeficient toplotne konvekcije znotraj in zunaj zidu. Po DIN 4701 - del 2 ([3] in [5]) smo uporabili: - za zunanji prenos toplote 22,7 W/m2K (81,7 kJ/ hm2K), - za notranji prenos toplote 7,7 W/m2K (27,7 kJ/ hm2K), - za notranji prenos toplote - strop 5,88 W/m2K (21,2 kJ/hm2K). As an example of the store we took a MERCATOR supermarket A new building which was built in 1999 and has a ground plan of 170 m x 110 m with a heiht of 8 m. The long facade is oriented towards SE-NW. The volume of the building is 170 x 110 x 8 = 149600 m3. For the apartment house we took a multi-family building. The building is oriented north-south, the ground plan is 16 m x 64 m. There is a ground floor plus 12 flats, plus attics. The height of each flat is 3m and the building is for 720 people. The volume is 40960 m3 (224 living units). The roof is flat and walking. For the single house we have analysed a house for one family in the Murgle area of Ljubljana. The ground plan of the house is 15 x 8 meters and is oriented north-south. 3 CLIMATE DATA The building types described in section 2 have been simulated in four different climatic conditions for Europe. We have used a Test Reference Year (TRY) [2] for the following countries: - United Kingdom - London, - Sweden - Stockholm, - Italy - Rome, - Slovenia - Ljubljana. Data for the TRY are made up from months of different years. For the Ljubljana Test Reference Year was taken data from years 1961 to 1980. Test Reference Year is a file of data which contains: 1) Number of days in the year (1 to 365), 2) External temperature (°C), 3) Relative humidity (%), 4) Wind velocity (m/s), 5) Total horizontal radiation (kJ/hm2) - if the value is zero then data for direct radiation is given, 6) Hour in the day, 7) Direct solar radiation (kJ/hm2) - if the value is zero then only the total solar radiation is given, 8) Difuse solar radiation (kJ/hm2) - if the value is zero then only the total solar radiation is given. 4 SIMULATIONS Simulations have been made using TRNSYS with building data (section 2) and with a Test Reference Year (section 3). For all cases we took the constant convec-tive heat-transfer coefficient inside and outside the wall. By DIN 4701 - Part 2 ([3] and [5]) we have used: - for external heat transfer 22.7 W/m2K (81.7 kJ/ hm2K), - for internal heat transfer 7.7 W/m2K (27.7 kJ/ hm2K), - for internal heat transfer 5.88 W/m2K (21.2 kJ/ hm2K). | gfin=i(gurMini5nLn 00-8_____ stran 505 I^BSSIfTMlGC U. Stritih - S. Muhi~ - P. Novak: Ra~unalni{ka analiza - A Computer Analysis Za vse primere je absorptivnost stene 0,6 (sončna absorptivnost stene). V primerih, ko imamo pred zidom steklo je celotna absorptivnost 0,6. Transmitivnost stekla reflectafloat je 57%, tako je absorptivnost stene 0,6 x 0,57 = 0,34. Reflektivnost okolice je 0,2. Za vse primere smo uporabili bruto prostornino. V tem primeru je prostornina od 20 do 30% večja od prostornine zraka v stavbah. V vseh primerih smo vzeli infiltracijo 0,6 izmenjav zraka na uro. V vseh primerih je bilo vključeno ogrevanje/ hlajenje z razvlaževanjem 50%. Vsi primeri so bili narejeni tako, da je celoten zrak za ventilacijo vstopa v stavbo z zunanjo temperaturo (brez rekuperacije toplote). Zaradi tega so individualni toplotni tokovi prikazani posebej. Za geografsko širino smo vzeli: Ljubljana 46,22 S, London 51,15 S, Stockholm 59,35 S, Rim 41,80 S. Vsa simuliranja so bila narejena za vse leto. V datoteki z rezultati imamo naslednje podatke: 1. TIME ura v letu (1 do 8760) 2. NO. OF DAY številka dneva v letu (1 do 365) 3. DATE datum dneva v letu (1.1. do 31.12) 4. Hour ura v dnevu (0 do 24) 5. Toutside zunanja temperatura (°C) 6. Tinside notranja temperatura v stavbi. (°C) - temperatura v coni 7. Qsensible senzibilni toplota (- ogrevanje, +hlajenje) (kJ/h) 8. Qsur konvekcija zraka iz vseh sten v coni (kJ/h) 9. Qinf infiltracijski energetski dobitki (kJ/h) 10. Qv ventilacijski energetski dobitki (kJ/h) 11. Qg_c notranji konvekcijski dobitki (kJ/h) 12. Qg_l latentni energetski dobitki (kJ/h) 13. Qg_r celotni notranji sevalni dobitki (kJ/h) 14. QUA_trans stacionarne izgube sten in oken v coni z uporabo »k« vrednosti, podane v izračunu (kJ/h) Prezračevalne izgube so izračunane pri svežem zraku z zunanjo temperaturo. Tako so te izgube/dobitki zelo pomembni in se izračunajo po enačbi: For all cases the absorbtivity of the walls was 0.6 (Solar Absorbtance of wall). In the cases where we have glass in front of the wall the total absorbtivity is 0.6. The transmitivity of the glass reflectafloat is 57 % so the absorbtivity of the wall is 0.6 x0.57 = 0.34. The reflectivity of the surroundings was 0.2. For all cases we have used the gross volume. In this case the volume is from 20 to 30 % bigger than the volume of the air in the building. In all cases we have used an infiltration of 0.6 volume air-changes per hour. In all cases heating/cooling was on with dehumidisation at 50% humidity. All cases were made so that all the air for ventilation comes into the building with the external temperature (without recuperation of heat). For this reason, individual heat fluxes are presented separately. For the locations the following latitude was used: Ljubljana 46.22 N, London 51.15 N, Stockholm 59.35 N, Rome 41.80 N. All simulations have been made for a whole year. In the results file we have the following data: 1. TIME hour in the year (1 to 8760) 2. NO. OF DAY number of day in the year (1 to 365) 3. DATE date for the day in the year (January the 1st to December the 31st) 4. Hour hour in the day (0 to 24) 5.Toutside external temperature (°C) 6. Tinside internal temperature in the build- ing (°C) - air temperature of zone 7. Qsensibile sensible energy demand (- heat- ing, + cooling) (kJ/hr) 8. Qsur total convection to air from all sur- faces within zone (kJ/hr) 9. Qinf infiltration energy gain (kJ/hr) 10. Qv ventilation energy gain (kJ/hr) 11. Qg_c internal convective gains (kJ/hr) 12. Qg_l net latent energy gains (kJ/hr) 13. Qg r total internal radiative gain (kJ/hr) 14. QUA trans stationary UA-transmission losses of walls and windows of zone using the u-values given in the transfer calculation section (kJ/hr) Ventilation losses are calculated for necessary fresh air with external temperature. So these losses/gains are very important and they are calculated using the equation: Qv . V .r.cp (Tvent -Tair ) kjer je: where: vent outside Ker so rezultati prikazani za vsak mesec posebej, lahko spremenimo prezračevalne rezultate zelo preprosto. Na enak način je izračunana tudi infiltracija, kjer smo uporabili 0,6 izmenjav zraka na uro. Since the results are shown separately for each hour we can change the ventilation results very easily. In the same way, infiltration is also calculated where we have used 0.6 of volume air-changes per hour. VH^tTPsDDIK stran 506 U. Stritih - S. Muhi~ - P. Novak: Ra~unalni{ka analiza - A Computer Analysis 5 REZULTATI Skupaj smo naredili 4 x 7 = 28 simuliranj za 8760 ur. Na naslednji sliki predstavljamo rezultate za pisarniško poslopje. Pozitivne vrednosti pomenijo hlajenje, negativne pa ogrevanje. 5 RESULTS Altogether we have made 4 x 7 = 28 simulations for 8760 hours. In the next figure we present the results for the office building . Positive values mean cooling and negative values mean heating. Pisarna v Stockholmu / Office Stockholm 4,00E+06 kJ/h 2,00E+06 0,00E+00 -2,00E+06 -4,00E+06 -6,00E+06 -8,00E+06 -1,00E+07 -1,20E+07 I i I IIH Mife.1 & m Pisarna v Ljubljani / Office Ljubljana 4,00E+06 kJ/h 2,00E+06 -2,00E+06 -4,00E+06 -6,00E+06 -8,00E+06 -1,00E+07 urnimmm vummi Pisarna v Londonu / Office London 1,00E+06------------------------- 0,00E+00 ------------------ -1,00e+06 - 1 ^ -2,00E+06 -3,00E+06 -4,00E+06 -5,00E+06 -6,00E+06 -7,00E+06 -8,00E+06 Pisarna / v Rimu / Office Rome 6,00E+06 kJ/h 4,00E+06 2,00E+06 0,00E+00 -2,00E+06 -4,00E+06 -6,00E+06 -8,00E+06 1 M—PfJUM^nHiiii Sl. 1. Primer senzibilnih obremenitev v času enega leta Fig. 1. An example of sensible heat loads for a period of one year Za inženirsko uporabo so najpomembnejše najmanjše in največje vrednosti. Na sliki 2 predstavljamo te rezultate za pisarniško poslopje. 6 SKLEP Ugotovili smo, da imata Stockholm in Ljubljana zelo podobne toplotne obremenitve, podobno kakor London in Rim. Razmerje obremenitev med Ljubljano in Rimom pa je 3:2. Na drugi strani so hladilne obremenitve podobne za Ljubljano in Stockholm, medtem ko za London in Rim ugotavljamo razlike, kar je posledica različnih klimatskih razmer. For engineering use the most important data are the minimum and maximum values. In Fig. 2 we present those values for the office building. 6 CONCLUSION We found that Stockholm and Ljubljana have very similar heating loads as do London and Rome. But the ratio between loads in Ljubljana and Rome is 3:2. On the other hand, cooling loads are similar for Ljubljana and Stockholm whereas for London and Rome we found a difference which is the consequence of different climatic conditions. 7 LITERATURA 7 REFERENCES [1] TRNSYS: Transient System Simulation Programme, Wisconsin Madison, USA. [2] Test Reference Year for Ljubljana, London, Stockholm and Rome. [3] Recknagel, Sprenger, Schramek (1995) Taschenbuch fur Heizung und Klima Technik. Oldenburg Verlag, Wien. [4] Project documentation. [5] ASHRAE Fundamentals 1997. gfin^OtJJlMISCSD 00-8 stran 507 |^BSSITIMIGC dan / day dan / day 2,00E+06 dan / day dan / day U. Stritih - S. Muhi~ - P. Novak: Ra~unalni{ka analiza - A Computer Analysis Pisarna v Stckholmu - maks obremenitev Office Stockholm - max load 2,50E+06 2,00E+06 1,50E+06 - 1,00E+06 - 5,00E+05 0,00E+00 -5,00E+05 -1,00E+06 -1,50E+06 --------------------------------------------- 06 ura dneva / hour of day Qsensibile Qsur Qinf Qv Qg_c 0,00E+00 -2,00E+06 -4,00E+06 -6,00E+06 -8,00E+06 -1,00E+07 -1,20E+07 Pisarna v Stockholmu - min obremenitev Office Stockholm - min load 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Qsens ibile Qsur Qinf Qv Qg_c ura dneva / hour of day Pisarna v Ljubljani - maks obremenitev Office Ljubljana - max load Pisarna v Ljubljani - min obremenitev Office Ljubljana - min load 3,50E+06 J/h 3,00E+06 2,50E+06 2,00E+06 1,50E+06 1,00E+06 5,00E+05 0,00E+00 -5,00E+05 -1,00E+06 2,00E+06 kJ/h Qsensibile Qsur -2,00E+06 Qinf Qv -4,00E+06 Qg c -6,00E+06 -8,00E+06 -1,00E+07 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Qsensibile Qsur Qinf Qv Qg_c ura dneva / hour of day ura dneva / hour of day Pisarna v Londonu - maks obremenitev Office London - max load Pisarna v Londonu - min obremenitev Office London - min load 2,00E+06 kJ/h 1,50E+06 1,00E+06 5,00E+05 0,00E+00 -5,00E+05 -1,00E+06 -1,50E+06 -2,00E+06 -2,50E+06 20 21 22 23 24 Qsensibile Qsur Qinf Qv Qg_c ura dneva / hour of day 2,00E+06 kJ/h 1,00E+06 0,00E+00 -1,00E+06 -2,00E+06 -3,00E+06 -4,00E+06 -5,00E+06 -6,00E+06 -7,00E+06 -8,00E+06 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Qsensibile Qsur Qinf Qv Qg_c ura dneva / hour of day 5,00E+06 kJ/h 4,00E+06 3,00E+06 2,00E+06 1,00E+06 Pisarna v Rimu - maks obremenitev Office Rome - max load Pisarna v Rimu - min obremenitev Office Rome - min load 1,00E+06 kJ/h 5,00E+05 0,00E+00 -5,00E+05 -1,00E+06 -1,50E+06 -2,00E+06 -2,50E+06 -3,00E+06 20 21 22 23 24 —•— Qsensibile Qsur Qinf IQv ura dneva / hour of day ura dneva / hour of day Sl. 2. Največje in najmanjše obremenitve za pisarniško zgradbo Fig. 2. Maximum and minimum loads for office building Naslov avtorjev: dr. Uroš Stritih Simon Muhič prof.dr. Peter Novak Fakulteta za strojništvo Univerze v Ljubljani Aškerčeva 6 1000 Ljubljana Authors’ Address: Dr. Uroš Stritih Simon Muhič Prof.Dr. Peter Novak Faculty of Mechanical Engineering University of Ljubljana Aškerčeva 6 1000 Ljubljana, Slovenia Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 VBgrTOEBS stran 508 3,00E+06 kJ/h 2,00E+06 kJ/h h 0,00E+00 h h h h 0,00E+00 -1,00E+06 h h © Strojni{ki vestnik 46(2000)8,509-516 ISSN 0039-2480 UDK 536.24:546.212:66.06:628.16.04/ © Journal of Mechanical Engineering 46(2000)8,509-516 ISSN 0039-2480 UDK 536.24:546.212:66.06:628.16.04/ .09:537.84 .09:537.84 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Prepre~evanje izlo~anja vodnega kamna na povr{inah prenosnikov toplote z uporabo naprave za magnetno obdelavo vode The Preventation of Surface Precipitation on Heat Exchangers Using a Magnetic Water-Treatment Device Andrej Pristovnik - Lucija ^repin{ek Lipu{ - Jurij Krope V nalogi predstavljamo metodo za nadzor vodnega kamna na temelju magnetne obdelave vode (MOV) v prenosnikih toplote. Podali smo teoretičen pregled tvorbe kotlovca pri industrijskih prenosnikih toplote s poudarkom na obarjanju kalcijevega karbonata (CaCO3) in kalcijevega sulfata (CaSO4) ter osnovne izračune za uspešno uporabo naprav MOV pri preprečevanju nastajanja vodnega kamna. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: prenosniki toplote, zaščita proti kotlovcu, magnetna obdelava vode, magnetohidrodinamika) Magnetic water treatment (MWT), a water-conditioning method for scale control in heat exchangers (HEs), is discussed. The theoretical possibilities of scale formation in industrial processes with the emphasis on the precipitation of CaCO3 and CaSO4 as the main scale components, are reviewed. Some preliminary calculations for a theoretical understanding of the scale problem in HEs and its prevention using MWTs are contributed. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: heat exchangers, scale control, magnetic water treatment, magnetohydrodynamic) 0 UVOD Problem izločanja vodnega kamna se pojavlja pri vseh tehnoloških procesih, ki uporabljajo naravno vodo. To pa še posebej velja v primeru uporabe prenosnika toplote, pri katerem pride do povišanja temperature in posledično do prenasičenja soli, ki tvorijo vodni kamen (predvsem CaCO3 in CaSO4). Obstaja več dobro znanih in uporabnih metod za preprečevanje nastajanja vodnega kamna. Uporaba nekaterih pomeni velik finančni strošek druge pa onesnažujejo okolje. V zadnjih letih se kot alternativa kemičnim metodam vedno bolj uveljavlja t.i. magnetna obdelava vode (MOV). Čeprav je metoda znana že petdeset let in z ekonomskega in okoljevarstvenega vidika zelo sprejemljiva, prav procesna industrija še naprej dvomi o njeni učinkovitosti in uporabi ([1] do [4]). 1 NASTANEK VODNEGA KAMNA Naravna voda je dejansko bogata raztopina/ disperzija mnogih ionov: Ca2+, Mg2+, Na+, K+, HCO3, SO42 in Cl. Ioni Na+, K+ in Cl - so inertni, preostali pa so vključeni v t.i. medfazno ravnotežje. Zaradi 0 INTRODUCTION The build-up of scale deposits is a common and costly problem in many industrial processes which use natural water supplies, especially in heat-exchange processes, where a high oversaturation of scale-forming components (i.e. CaCO3 and CaSO4) is established. There are many well-known scale-prevention methods, but they are costly and environmentally unfriendly. MWT is being used more and more as an alternative method for scale control. The process industry remains skeptical about this non-chemical method despite its long history and examples of favorable economic benefits ([1] to [4]). 1 SCALE FORMATION Natural waters are rich solution/dispersion systems which contain the ions: Ca2+, Mg2+, Na+, K+, -HCO3-, SO42- and Cl-. The Na+, K+ and Cl ions are inert, while the others are incorporated into an inter- gfin^OtJJlMISCSD 00-8 stran 509 |^BSSITIMIGC A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation sprememb obratovalnih razmer (sprememba tlaka, temperature, vrednosti pH) pride do prenasičenja in soli se v obliki vodnega kamna izločajo na stene cevi, prenosnikov toplote in drugih naprav, ki so v stiku z vodo. Najpomembnejši parameter za nadzor vodnega kamna je delež kalcijevih ionov Ca2+. Določimo ga s pomočjo t.i. karbonatnega ravnotežja ((1) do (4)). Parametra (c) in (K) pomenita koncentracijo in konstanto ravnotežja. CO2(g)+H2OoH2CO3, H2CO3<->H++HCO3, phase equilibrium. Due to the natural supersatura-tion of the supplied water or supersaturating due to changed operating conditions (such as a pressure drop, temperature or pH increase) hard scale precipitates in pipelines and on the walls of equipment. The most important parameter in scale control is the concentration of Ca2+ ions, determined by carbonate equilibrium ((1) to (4)), where the parameter c is the concentration and parameters K is the equilibrium constant. Kg = p c H2CO3 CO2 HCO3 ^H++CO3- CaCO3(s)^Ca2++CO2-, K1 K c H2CO3 c -c H+ CO32 - K =c (1) (2) (3) (4). Iz pogoja o električni nevtralnosti (5) in z upoštevanjem ionskega produkta vode (6) lahko izpeljemo odvisnost koncentracije kalcijevih (Ca2+) ionov kot funkcije vrednosti pH in temperature. From the condition of the solution’s electric neutrality (5) and the water dissociation equilibrium (6), the concentration of Ca2+ ions can be derived as a function of pH and temperature. 2cCa2+ + cH+ = 2cCO23 - + cHCO-3 + cOH- HO<->H++OH- Kw=cH+cOH- KW -cH2+ + ( cH2+-KW ) +8cH2+-K\2 + H K 1/ 2 4c (5) (6) (7). Konstante ravnotežja so odvisne od temperature (7). V naravnih vodah (pH < 7) vodi zvišanje temperature in vrednosti pH do znižanja ravnotežne koncentracije Ca2+ ionov (7). Pri znižanju tlaka pride do znižanja koncentracije H CO3 (1) in posledično s povečevanjem vrednosti pH pospešeno obarjanje CaCO3 ((2) do (4) in (7)). S temperaturo (do 40 oC) se zvečuje topnost CaSO4, pri višjih temperaturah (okoli 100 oC) pa naglo zmanjšuje. Iz opisanega je razvidno, da se bo v nizkotemperaturnih sistemih v glavnem izločal kalcijev karbonat (CaCO3) in v visokotemperaturnih sistemih (toplovodi, uparjalniki, prenosniki toplote) pa kalcijev sulfat (CaSO4). 2 ZMANJŠANJE UČINKOVITOSTI PRENOSA TOPLOTE Obloge vodnega kamna, ki nastanejo na površinah prenosov toplote, zmanjšujejo pretočne zmogljivosti in predvsem učinkovitost prenosnikov toplote ter s tem zvišujejo investicijske, obratovalne in vzdrževalne stroške. Brez primerne obdelave napajalne The equilibrium constants in equation (7) are temperature dependent. In natural waters (with a pH less than 7), a rise in temperature and pH leads to a reduction of the Ca2+ equilibrium concentration according to equation (7). The pressure drop leads to a lower concentration of H2CO3 according to equation (1) and causes CaCO3 precipitation with a pH increase according to eqs. ((2) to (4) and (7)). The solubility of CaSO4 increases as the temperature increases to approximately 40oC and then rapidly decreases at higher temperatures around 100oC. As a result, CaCO3 is the main scale component in low-temperature water systems, while in high-temperature water systems (especially in high-pressure heat exchangers and boilers) CaSO4 prevails. 2 HEAT EXCHANGE REDUCTION The scale formed on heated surfaces reduces the flow capacity and heat exchange efficiency which leads to higher investment, operation and maintenance costs. Hard scale can be a severe industrial problem without properly supplied water condition- VBgfFMK stran 510 A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation vode so tako nastale trdovratne obloge težak industrijski problem; terjajo periodično čiščenje z mehanskimi postopki in jedkanjem s solno kislino. Naslednja ocena bo pokazala, kako vodni kamen izrazito znižuje prenos toplote. Moč toplotnega toka P skozi kovinsko steno površine S pri temperaturni razliki DT je za nov prenosnik st (sl. 1.a) določena z enačbo (8). Prestopnostni koeficient a1 je tu praktično enak konvekcijskemu koeficientu plasti vode na obeh straneh stene. Konvekcijski koeficient kovine je namreč bistveno višji kakor za vodo ing. It demands periodic cleaning using mechanical methods and HCl etching. The following preliminary calculations show how scale drastically reduces the exchange of heat. With a new wall of a HE (Fig. 1/a), the heat-flow intensity (P1) through the metallic wall of area S at a temperature difference DT is determined by equation (8), where the heat transition coefficient (a1) is practically equal to the convection coefficient of the water layer on both sides of the wall due to the much higher value of the heat-conduction coefficient of the metal P1 =a^S-DT (8). Obloge vodnega kamna (sl. 1.b) znižujejo The formation of scale (Fig. 1/b) reduces moč toplotnega toka P’ in je ta določen z enačbo (9). the heat flow intensity (P’) according to equation (9), Tukaj se lahko celokupni prestopnostni koeficient a’ where the total heat-transition coefficient (a’) can be izračuna iz a1 nove stene in a2 nastalih oblog po calculated using a1 of the new wall and a2 of the enačbi (10). Velja za postavko iste temperaturne razlike formed scale according to equation (10) at the same med ogrevano in hladilno vodo DT = DT + DT . temperature difference DT = DT + DT. The coeffi- Koeficient a2 je odvisen od celotne debeline oblog cient a2 depends on the total scale lining thickness Dy2 po zvezi (11), kjer je l2 toplotna prevodnost (Dy2) according to equation (11), where l2 is the heat vodnega kamna. conductivity of the scale. P' = a'-S-DT = a1-S-DT1=a2-S-DT2 a 1 1/a1 + 1/a2 Dy2 (9) (10) (11). (a) kovinska stena metal wall (b) | kovinska stena metal wall a- Sl. 1. Temperaturni krivulji skozi: (a) novo kovinsko steno in (b) skozi kovinsko steno z oblogo vodnega kamna Fig. 1. The temperature curve through a new metallic wall (a) and through a metallic wall covered with scale (b) Preglednica 1 prikazuje nekaj vrednotenj Table 1 represents some estimations for the relativnega zmanjšanja učinkovitosti prenosa toplote relative drop of the heat-exchange efficiency (z) de- x, ki je definirana z enačbo: fined by equation: z = P1 -P, = 1- a, 1 1 + a1Dy2/ l2 (12) gfin^OtJJlMISCSD 00-8 stran 511 |^BSSITIMIGC A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation Preglednica 1. Relativna zmanjšanja učinkovitosti prenosa toplote (pri izbrani praktični vrednosti a1 = 500 W/m2K za kovinsko steno) zaradi oblog CaCO (l2 = 1,75 W/mK) oziroma CaSO (l2 = 0,50 W/mK) Table 1. Relative drops of heat-exchange efficiency at chosen practical values a1 = 500 W/m2K due to CaCO lining (l2 = 1.75 W/mK) and CaSO lining (l2 = 0.50 W/mK), respectively Dy2 z(CaCO3) z(CaSO4) 1,5 mm 5,5 mm ) 30% 60% 85% ) 60% 85% 95% 20 mm Rezultati potrjujejo praktične izkušnje, da zaradi nizke toplotne prevodnosti CaCO3 in CaSO4, celo tanke obloge vodnega kamna izrazito zmanjšujejo učinkovitost prenosa toplote. V visokotlačnih grelnih napravah je ta problem še posebej močno izražen, saj se v večinskem deležu izloča kalcijev sulfat, ki ima manjšo toplotno prevodnost od kalcijevega karbonata. V mnogih primerih se je izkazalo, da omogočajo naprave za magnetno obdelavo vode razmeroma učinkovit sistem za nadzor vodnega kamna. Eden od uspešnih preskusov naprav MOV domačega proizvajalca Panorama Ptuj [6] pomeni vgradnja le-teh v prenosnik toplote Toplotne oskrbe Maribor (TOM) [5]. Naprave so bile instalirane na ceveh s hladno napajalno vodo in so učinkovito preprečile nastanek vodnega kamna. V preglednici 2 sta predstavljena rezultata vgradnje naprav za magnetno obdelavo v prenosnika toplote. Results prove that even thin scale linings drastically reduce the heat-exchange efficiency because of the low heat of conductivity of the scale components CaCO3 and CaSO4. In high-pressure boilers the problem will be even greater due to the main scale component, CaSO4, which has a lower heat of conductivity than CaCO3. These theoretical predictions are in accordance with many practical results, where scale formation on HE surfaces demanded a preliminary treatment of the supplied water. In many cases MWT turned out to be a very efficient method for scale control. The installation of MWT devices to prevent hard scale in the HEs in the TOM town heating station [5] was one of the successful domestic tests of the Panorama Ptuj magnetic device [6]. These devices were installed on the cold water pipeline entrance of the HE and efficiently solved any problems with hard scale. Table 2 represents some observations on the scale in the two HEs which were supplied with magnetic ally treated water. Preglednica 2. Rezultati naprave za magnetno obdelavo proizvajalca Panorama Ptuj v toplotni postaji TOM-a Table 2. Results of Panorama Ptuj devices in the TOM station Prenosnik toplote HE star cevni register U old U-pipe register nov spiralni register new spiral register obloge ob vgradnji scale at MWT installation da yes ne none prvi pregled time of the first control 8 mesecev po vgradnji 8 months after installation 11 mesecev po vgradnji 11 months after installation stanje po prvem pregledu state after the first control obloge, odstranitev z vodnim visokotlačnim curkom present scale was removable with high-pressure water jet tanke plastne obloge, odstranitev z vodnim visokotlačnim curkom thin powder scale was removed with jet drugi pregled time of the second control 16 mesecev po vgradnji 16 months after installation 17 mesecev po vgradnji 17 months after installation stanje ob drugem pregledu state after the second control oblog ni bilo,površina je bila veliko bolj čista kakor pred samo vgradnjo without a new scale, surfaces were cleaner than before the installation time enako kakor pri prvem pregledu the same as at the first control 3 NADZOR VODNEGA KAMNA V PRENOSNIKIH TOPLOTE V naravni vodi, bogati z raztopljenimi/ dispergiranimi snovmi, delujejo naprave za magnetno obdelavo vode neposredno na samo stabilnost in 3 THEORETICAL PRINCIPLES OF MWT SCALE PREVENTION ON HE SURFACES The nature of MWT devices acting on supplied water as a rich solution/dispersion system is to alter its crystallization habits and dispersion stability to form VBgfFMK stran 512 A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation kristalizacijo dispergiranih delcev. Kristali, ki se izločajo po obdelavi, so večji in modificirani. Prav na teh kristalih se neposredno iz vode izloči večji del soli, tako da se na stenah naprav nabere neprimerno manj vodnega kamna. Ob pretakanju vode skozi napravo za magnetno obdelavo prihaja do sprememb, ki pa se izražajo (najverjetneje) v spremenjeni ionski hidrataciji prek magnetohidrodinamičnega premika ionov in koncentracijskega vpliva na dispergirane delce v sami napravi MOV [7]. Izračuni kažejo, da se med magnetno obdelavo vode agregatne tvorbe, sestavljene iz CaCO3 in CaSO4 trdno sprimejo. Iz samega načela staranja kristalov namreč kosmiči, v katerih so delci med seboj šibko povezani, niso tako zaželeni kakor goste agregatne tvorbe [8]. Po teoriji DLVO (Deryagin, Landau, Verwey, Overbeck) ([9] in [10]) smo opravili numerično analizo koagulacije in kosmičenja nemagnetnih delcev vodnega kamna in prišli do sklepa, da v naravnih vodah prevladuje koagulacija, ki je odvisna od same naprave MWT, medtem ko je zaradi nizke vrednosti Hamakerjeve konstante in nizke magnetne susceptibilnosti pri večjih delcih (a > 0,1 mm) mogoča le kosmičenje. Po drugi strani pa se bodo magnetohidro-dinamično nastali kosmiči pod vplivom turbulentne pulzacije razbile. Do pulzacije prihaja v večini naprav MOV, kjer je priporočena pretočna hitrost od 0,5 do 2 m/s. Ob preseženi vrednost Reynoldsovega števila (104) imamo opraviti s turbulentnim tokom Re = Parametra h in r pomenita viskoznost in gostoto vode. Pri pretočni hitrosti 0,5 m/s je kritična velikost delovnega preseka znotraj naprave MOV 2 cm in pri 2 m/s pa 0,5 cm. Iz pulzacijske teorije [11] smo za izračun pulzacijske dolžine (b) in pulzacije delcev(v) s polmerom (a) izpeljali sistem enačb: r- bigger modified crystals, which in suspended form offer surfaces for scale precipitation and in that way hard scale formation indirectly prevails on equipment walls. The change in the water’s behaviour when the water flows through the magnetic field is most probably a result of altered ion hydration, by magne-tohydrodynamic shifts of ions and concentration effects on the dispersed particles in the working channel of the MWT device [7]. Some calculations have been made showing that all aggregates, formed from scale components (CaCO3 and CaSO4) during MWT, are compact-strongly adhered. In other words, the flocks in which constituent particles are weakly bonded are not as favorable for scale prevention as the compact aggregates according to the principles of crystal aging [8]. A numerical analysis of the coagulation and flocculation of the nonmagnetic scale components, based on the Deryagin, Landau, Verwey, Overbeck theory ([9] and [10]), has been made. It offered an estimation that in natural waters only flocculation from big particles (with radius a > 0,1 mm) is possible due to the low Hamaker constant and low magnetic susceptibility of these components, while a coagulation prevails and depends on the MWT working conditions. On the other hand, the magnetohydrody-namically formed big flocks will be shattered by turbulent pulsations which appear in the majority of practical MWT devices, where the recommended values of water flow velocity are in range from 0.5 to 2 m/s for efficient anti-scale treatment. The Reynolds number Re, defined by equation (13), characterizes turbulent flow, if it is greater than 104 (13). h The parameter h is the viscosity and r is the mass density of water. For a water flow of velocity 0.5 m/s, the critical thickness of the working channel (d) is 2 cm, and for 2 m/s, the critical thickness is 0.5 cm. From the turbulent pulsations theory [11], the equation system was obtained for the evaluation of the pulsation length (b) and the pulsation for a particle with radius a (vb). b = 207 d 0,17v logRe/ 7 Re7/4 Stabilni kosmič z 10kT vezno energijo med delci (k je Boltzmannova konstanta) lahko razbijemo s turbulentno pulzacijo samo, če je gostota kinetične energije rv2/2 večja od gostote vezne energije 10k T/ (4pa3/3). Določimo lahko ti. kritični polmer kristalnega delca (a*): 1/3 Re 1/ 4 (14) (15) A stable flock with a 10k T bonding energy between constituent particles (k is the Boltzmann constant) would be shattered by turbulent pulsation, if the kinetic energy density rv2/2 were greater than the bonding energy density 10kBT/(4pa3/3). A crystal particle radius is therefore: A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation 3 15kBT / prvb (16). Tako je pri v = 0,5 m/s kritični polmer 0,25 mm in 0,13 mm pri v = 2 m/s. Povzamemo lahko, da bo za priporočene pretočne hitrosti proizvajalcev naprav MOV turbulenca razbila CaCO3 in CaSO4 kosmiče. V suspendirani obliki bodo ostali le najbolj močno vezani agregati. V primerjavi s kemijskimi metodami priprave vode za nadzor vodnega kamna je magnetna obdelava še najbolj podobna suspendiranju kristalnega prahu. Naslednji izračuni določajo potrebno količino prahu za preprečevanje izločanja CaCO na stenah prenosnikov toplote z relativno površino SHE = S storn Vvode, kjer sta Sstene površina sten in Vvode Da bi se zagotovil hiter prenos toplote, so v skladu z enačbo (17) [12] priporočane visoke vrednosti SHE, in sicer med 100 in 1000 /m. dT = a dt cpr V enačbi (18) je iz kvocienta x oborjene mase v jedru vode (dm ) in mase na stenah (dm ) razvidno, da se bo vodni kamen nalagal v tanjših oblogah pri nižjih vrednostih SHE. The critical radius a is 0.25 mm for a water flow of velocity v = 0.5 m/s and a is 0.13 mm for v = 2 m/s. A theoretical conclusion could be made for all recommended ranges of water flow velocity that turbulence will deaggregate CaCO3 and CaSO4 flocks. Only highly adhered aggregates will remain in a suspended form. In a comparison with chemical scale-prevention methods, the suspending of crystal powder is the most similar to the MWT method. The following calculation estimates that the necessary amount of powder for the prevention of CaCO3 precipitation on the walls of a HE with a relative surface: SHE = S l/V , where S ll is the area and V is the water volume. wae To ensure a quick heat exchange, high values of SSE from 100 to 1000 /m are recommended according to equation (17) [12]. DTS (17). x dm rV dms In this relationship for the heating rate dT/dt, the parameter cp is the heat capacity of water. A thinner scale lining will be formed at lower values SHE , as can be predicted from the x-quotient (of precipitated mass in the bulk of water-dmv and precipitated mass on the walls - dms) in equation (18). So, the optimal value SHE in HE designing should be found. (18). rS rS s wall s HE V modificirani obliki sta enačbe za hitrost kristalne rasti (r) določila Nancollas in Reddy [13], in sicer na podlagi obarjanja iz jedra raztopine s temperaturo T na površino naprav s temperaturo T ((19) in (20)). Pri tem velja, da je parameter k določen empirično, MCaCO3 je relativna molska masa kalcijevega karbonata in R splošna plinska konstanta. The relationship of crystal growth rate r has been determined by Nancollas and Reddy [13] and is represented by equations (19) and (20) in a modified form for precipitation in the bulk of a solution with temperature T1 and on the equipment walls with temperature T2, where k is an empirical parameter, MCaCO3 is the relative molecular mass of CaCO3 and R is the universal gas constant. r = kMCaCO exp| RT1- \Spowder b1 DG -DG SHE=kMC exp RT2 Sb wall 2 (19) (20) (21) Kristalna rast je odvisna od sestave raztopine in trdnine: - stopnje prenasičenja b, ki je ob stenah prenosnikov toplote (b2) višje kakor v jedru raztopine (b1), in od - aktivacijske energije DG, ki je odvisna od kristalne faze. V primeru obarjanja CaCO sta kristalni fazi kalcit in aragonit. V suspendiranem prahu, nastalem z magnetno obdelavo, je opažen povečan delež The crystal growth rate depends on solution and solid phase composition by: - b supersaturation degree (defined by 21), which is higher at the HE walls (b2) than in the bulk of solution (b1); - DG activation energy depending on crystal phase. In the case of CaCO precipitation, crystal phases aragonite and calcite are formed. A powder, formed from magnetically treated water, has an increased VH^tTPsDDIK stran 514 A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation aragonita. Za hipotetični primer vzamemo vrednost AG1 za aragonit in vrednost AG2 za kalcit. Z zamenjavo r in r SHE v enačbi (18) z izrazoma (19) in (20) dobimo zvezo (22) za količino prahu, ki je potrebna za učinkovit nadzor CaCO oblog: fraction of aragonite. In an ideal case a DG1 value could be taken for aragonite and a DG2 for calcite. With the substitution rv and rsSHE in (18) by (19) and (20), equation (22) is obtained and a necessary powder surface is estimated: powder b1 x b2 exp DG1 RT DG2 RT (22) Da bi se učinkovito preprečile obloge trdega vodnega kamna za temperaturno območje 40 do 100oC in za zahtevano učinkovitost, je potrebna količina prahu S ah istega reda, kakor je površina sten prenosnikov toplote Sstene 4 SKLEP Za nadzor vodnega kamna na stenah prenosnikov toplote je potrebna optimizacija velikosti površine za prenos toplote glede na obratovalne razmere. Zraven kemičnih postopkov za zmanjšanje koncentracije Ca2+ ionov se priporoča uporaba naprav MOV. Dobro načrtovana naprava MOV, ki zagotavlja zadostno količino suspendiranih delcev v obliki praška, lahko učinkovito prepreči nastanek kotlovca. Problem učinkovitega načrtovanja naprav MOV je nezadostno poznavanje samega mehanizma delovanja teh naprav. Mehanizem je zapleten in je neposredno odvisen tudi od obratovalnih razmer in sestave napajalne vode. Na srečo so na temelju empiričnih izkušenj izdelali lepo število učinkovitih naprav MOV. S tem zadovoljujejo veliko povpraševanje po tej preprosti in cenovno ugodni rešitvi za preprečevanje nastanka vodnega kamna. For efficiency request |«A/fl2 and operational temperatures between 40oC and 100oC, the necessary powder surface S d should be of the same order as the surfaces of the heat exchanger walls Swall to effectively prevent hard scale. 4 CONCLUSION For scale control in HEs an optimization of the heat-exchange surface area is recommended for simultaneous high heat transition and scale prevention. In addition, besides chemical methods for the reduction of the Ca2+ concentration, the alternative method of MWT is recommended. A well-designed MWT device which assures the formation of a suspended scale powder with a surface area comparable to the exchange surface area can effectively prevent hard-scale formation. The prob-lem with designing MWT devices is an insufficient theoretical understanding of the MWT mechanism. The mechanism is complex and depends directly on operational conditions and the composition of the supplied water as a solution/dispersion system. Fortunately, numerous MWT devices of different constructions have been designed on an empirical basis resulting from several decades of testing and are available to satisfy a large demand for such easy and cheap solutions to industrial scale problems. 5 OZNAKE 5 SYMBOLS premer delca dolžina pulza koncentracija specifična toplota premer cevi aktivacijska energija prva konstanta ravnotežja pri disociaciji HCO druga konstanta ravnotežja pri disociaciji HCO plinska konstanta ravnotežja topnostni produkt ionski produkt vode empirična konstanta hitrosti kristalne rasti Boltzmannova konstanta molska masa masa moč toplotnega toka tlak a b c c p d DG K1 K2 Kg Ks Kw k kB M m P p m particle radius m pulsation length mol/L concentration J/kgK heat capacity m thickness of working channel J/mol activation energy ml/L equilibrium constant of the first step of H2CO3 dissociation ml/L equilibrium constant of the second step of H2CO3 dissociation mol m2/NL gas equilibrium constant mol2/L2 soluble product mol2/L2 dissociation product of water 1/mol m3s empirical constant of crystal growth rate J/K Boltzman constant kg/mol molar mass kg mass J/s heat flow intensity N/m2 gas pressure A. Pristovnik - L.^. Lipu{ - J. Krope: Prepre~evanje izlo~anja - The Preventation of Precipitation splošna plinska konstanta Reynoldsovo število hitrost kristalne rasti s raztopini hitrost kristalne rasti na kovinskih stenah površina absolutna temperatura čas hitrost pretoka hitrost turbulentne pulzacije debelina sloja vodnega kamna koeficient toplotne prehodnosti stopnja prenasičenja viskoznost koeficient toplotne prevodnosti gostota snovi učinkovitost nadzora vodnega kamna učinkovitost prenosa toplote R J/molK Re - r kg/m3s r kg/m2s S m2 T K t s v m/s v m/s Dy m a J/m2sK b mol2/L2 h Ns/m2 l J/msK r kg/m3 x - z - 6 LITERATURA 6 REFERENCES universal gas constant Reynolds number crystal growth rate in bulk of water crystal growth rate on walls surface area temperature time flow velocity turbulent pulsation velocity scale thickness heat transition coefficient supersaturation degree water viscosity heat conductivity mass density scale control efficiency heat exchange efficiency [I] Kittner, H.(1970) Wassertechnik 20(4), 136. [2] Tebenihin, E. F., B.T. Gusev (1970) Obrabotka vody magnitnym polem v teploenergetike. p.145, Izdatel‘stvo Energija Moskva, Moskva. [3] Grutsch, J. F. (1977) USA/USSR Symposium on physical-mechanical treatment of wastewaters; p. 44, EPA-Cincinati. [4] Grutsch, J. F., J.W. McClintock (1984) Corrosion and deposit control in alkaline cooling water using magnetic water treatment at Amoco’s largest refinery. CORROSION/84, No.330, Texas. [5] Krope, J., L. Crepinsek (1994) Magnetic water treatment for process systems. Research Project B2-6504-0795-94, Ministry for Science and Technology, Slovenia. [6] OPz Panorama Ptuj (prodajni prospekt), Osojnikova 1, 2250 Ptuj, Slovenia. [7] Krope, J., L. Crepinsek (1998) Magnetohydrodynamics of colloid systems. Research Project L2-06990-0795-98, Ministry for Science and Technology, Slovenia. [8] Khamskii, E.V.(1969) Crystallization from solutions. Consultants Bureau, New York-London. [9] Voyutski, S. (1978) Colloid chemistry. MIR publisher Moscow. [10] Hunter, R.J. (1996) Introduction to modern colloid science. Oxford Science Publications, New York. [II] Kulskii, L.A., V.Z. Kochmarskii, V. V. Krivtsov (1983) Intensifying and destabilizing factors of magnetic antiscale treatment of water. Himiya i tehnologija vody, Vol. 5, No. 4, 296-301. [12] Krope, J., E. Kiker (1996/98) Planing and dimensioning of heat recuperaters in water / steam systems. Research Project Maribor. [13] Nancollas, G. H., M.M. Reddy (1974) Crystal growth kinetics of minerals encountered in water treatment processes. Aqueous-Environmental Chemistry of Metals, New York. Naslova avtorjev: mag. Andrej Pristovnik dr. Lucija Črepinšek Lipuš Fakulteta za strojništvo Univerze v Mariboru Smetanova 17 2000 Maribor prof. dr. Jurij Krope Fakulteta za kemijo in kemijsko tehnologijo Univerze v Mariboru Smetanova 17 2000 Maribor Authors’ Addresses: Mag. Andrej Pristovnik Dr. Lucija Črepinšek Lipuš Faculty of Mechanical Eng. University of Maribor Smetanova 17 2000 Maribor, Slovenia ProfDr. Jurij Krope Faculty of Chemistry and Chemical Technology University of Maribor Smetanova 17 2000 Maribor, Slovenia Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 VBgfFMK stran 516 © Strojni{ki vestnik 46(2000)8,517-524 ISSN 0039-2480 UDK 621.574.013:620.92 Pregledni znanstveni ~lanek (1.02) © Journal of Mechanical Engineering 46(2000)8,517-524 ISSN 0039-2480 UDC 621.574.013:620.92 Review scientific paper (1.02) Analiza eksergijskih tokov absorpcijske hladilne naprave An Analysis of Exergy Flows in an Absorption Chiller Vasilije Vasi} - Jurij Krope - Darko Gori~anec V prispevku je podan postopek analize eksergijskih in anergijskih tokov v enostopenjski absorpcijski hladilni napravi z delovnim medijem LiBr/HO ter postopek izračuna eksergijskega izkoristka v odvisnosti od stopnje uporabe naprave. Nakazana je prednost absorpcijske hladilne naprave pred kompresijsko hladilno napravo, ki se izkazuje v možnosti uporabe eksergijsko revne odpadne toplote in v rabi alternativnih energetskih virov. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: naprave hladilne, naprave absorpcijske, tok energijski, izkoristek eksergijski) This paper presents our analysis of the exergy and anergy flows and exergy efficiency of an absorption chiller which has been calculated for all areas of the devices exploitation. This analysis has been implemented on a single-stage absorption chiller with LiBr/HO as a working media. We wish to show the advantages of sorption chillers, in our case absorption chillers, in comparison to compressor chillers in utilizing low exergy, rejected heat and in the use of alternative energy sources. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: thermodynamics, absorption chiller, exergy flow, efficiency) 0 UVOD Potreba po hlajenju postaja v sodobnem svetu vedno večja zaradi večjih zahtev po bivalnem ugodju, kar pa je povezano z zahtevnejšimi tehnološkimi procesi. Hlad tako postaja enakovreden produkt električni energiji in toploti. Hlad se pridobiva najpogosteje s kompresorskimi hladilnimi napravami, katerim postajajo vse bolj konkurenčne absorpcijske hladilne naprave in namesto mehanske (električne) energije uporablja toploto. Absorpcijska hladilna naprava (sl. 1) je sestavljena iz dveh obtokov - gretja in hlajenja, ki sta med seboj povezana. Posebnost naprave je toplotni kompresor, medtem ko so elementi hladilnega obtoka enaki kakor pri kompresorski hladilni napravi. Delovne snovi absorpcijske hladilne naprave so okolju precej bolj prijazne od tistih pri kompresijski hladilni napravi. Najpogosteje se uporabljata delovni snovi - binarna zmes LiBr/HO ali H2O/NH3. 0 INTRODUCTION The demand for cooling is growing as peoples’ expectations of a more comfortable life, surrounded by technology continues to increase. Cooling is becoming a product equivalent to electricity and heat. The cooling process is most frequently carried out compressor chillers, of which absorption chillers are becoming increasingly significant. In contrast to the compressor chillers, absorption chillers are driven by heat rather than electricity. An absorption chiller (Figure 1) works using two interconnected cycles - heating and cooling. The device’s speciality is its thermal compressor, while the cooling cycle is undertaken using the same components found in compressor chillers. The working media of absorption chillers are environmentaly friendly compared to those used by compressor chillers because the most frequently used working media for absorption chillers are binary mixtures of LiBr/H2O and H2O/NH3. gfin^OtJJlMISCSD 00-8 stran 517 |^BSSITIMIGC V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows 1 DELOVANJE NAPRAVE Delovanje absorpcijske hladilne naprave poteka, prikazano posplošeno, na dveh tlačnih nivojih, treh temperaturnih nivojih in treh nivojih koncentracije hladiva [1]. Generatorju in uparjalniku se toplota dovaja na najvišjem oz. najnižjem temperaturnem nivoju, medtem ko se okolici toplota predaja na srednjem temperaturnem nivoju iz kondenzatorja in absorberja (sl. 1). Vezava zunanjega obtoka kondenzatorja in absorberja je lahko ločena (vzporedna vezava) ali pa povezana (serijska vezava). Učinkovitejši način je serijska vezava [1], ki je uporabljena v primeru analize eksergijskih tokov. Izhodišče vsake termodinamične analize procesa ali postroja je energijska bilanca (prvi glavni zakon termodinamike). V apsorbcijski hladilni napravi 1 THE PERFORMANCE OF THE ABSORPTION CHILLER The functioning of an absorption chiller can be described simply as a process between two pressure levels, three temperature levels and three levels of coolant concentration [1]. Heat is provided to the generator and evaporator at either the highest or lowest temperature levels, respectively. In the mean time, heat is delivered from the absorber and the condenser to the surroundings at the medium temperature level (Figure 1). The external-flow connection to the condenser and the absorber can be either independent (parallel flow) or connected (serial flow). Serial connection has proved to be the more efficient method [1] and has been adopted when presenting our analysis of exergy flows. At the beginning of each thermodynamic analysis of thermal processes or a thermal plant we use the energy balance (First Law of Thermodynam- 7 H-----* Generator Generator 11 r Porabniki tople sanitarne vode (ali hladilni stolp) Consumer of hot domestic water (or cooling tower) Prenosnik toplote Heat Exchanger Vir toplotne energije Driving Heat Source Toplotni kompresor Thermal Compressor Sl. 1. Shema absorpcijske hladilne naprave Fig. 1. Model of the absorption chiller 00-8 VH^tTPsDDIK stran 518 V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows imamo različne oblike energij (npr. toplotna, električna), katerih vrednost se kaže v stopnji zmožnosti za pretvarjanje v druge oblike energij. Popolnoma spremenljiv del energije v druge oblike energij se imenuje eksergija, nespremenljiv del pa anergija. Vse energije preračunamo na enako osnovo - eksergijo. Analiza eksergijskih tokov, ki temelji na drugem glavnem zakonu termodinamike, ima nalogo določiti: mesta nepovračljivosti, velikost nepovračlji-vosti, smer odvijanja procesov in celotno učinkovitost naprave. Pri analizi eksergijskih tokov se ne omejimo samo na analizo popolnosti procesov v napravi, temveč tudi na procese s toplotno menjavo delovne snovi s toplotnimi prejemniki in medsebojnimi vplivi na okolje [2]. Velikost nepovračljivosti - anergijskih tokov je praviloma odvisna od vrste opreme, delovne snovi in pogojev obratovanja. Osnovni vzroki nepovračljivosti energijskih procesov v absorpcijski hladilni napravi so [3]: - ohlajanje pare s temperature v generatorju na temperaturo kondenzacije, - dušenje hladilnega sredstva z dušilnim ventilom s tlaka kondenzacije na tlak uparjanja, - segrevanje pare z uparjalne temperature na temperaturo absorpcije, - prenos toplote v prenosniku toplote termičnega kompresorja, - segrevanje s hladivom bogate raztopine, - dušenje s hladivom revne raztopine za prenosnikom toplote in - prenos toplote na zunanje nosilce toplote v zunanjih obtokih. Kljub želji po zmanjšanju ali celo preprečitvi nastanka nepovračljivosti procesov imamo v dejanski absorpcijski hladilni napravi na nekatere nepovračljivosti zelo malo ali povsem nobenega vpliva. 2 PRERAČUN EKSERGIJSKIH TOKOV Preračun eksergijskih tokov je izveden na podlagi podatkov s preglednice 1 in literature ([1] in [4]) z določitvijo specifične eksergije snovnega toka, v karakterističnih točkah naprave (sl. 1 in 2). Specifična eksergija snovnega toka pove, koliko dela pridobi enota masnega toka pri povračljivem medsebojnem delovanju z okoljem [2]. Specifična eksergija snovnega toka v karakterističnih točkah naprave v hladilnem in zunanjem tokokrogu določimo z enačbo: ics). In the absorption chiller different forms of energy occur (e.g. heat, electricity), their values are reflected through their ability to convert to other forms of energy. The fully convertible part of energy as another form of energy is called exergy (availability) and the unconvertible is called anergy. We therefore calculate all energy forms on the same basis – exergy. The analysis of exergy flows, according to the Second Law of Thermodynamics, is the a task of determining: places of irreversibility, the direction of occurred processes and the effectiveness of the whole device. When performing the analysis of exergy flows we did not only analyze the perfection of the processes in the device, but we also focussed on the processes which consider heat interaction with the working media and the heat recipients as well as the device’s mutual interaction with the environment [2]. How big are the irreversibilities – anergy flows usually depend on the type of equipment, the working fluid and the operating conditions. The basic causes of irreversibilities of the energy processes in absorption chillers are [3]: - steam cooling from the temperature in the generator at the condensing temperature; - throttling the cooling media with a throttle valve from the condensing pressure to the evaporation pressure; - warming up the vapor from the evaporation temperature up to the absorption temperature; - warming up with coolant-rich solution; - throttling with coolant-poor solution behind the solution heat exchanger; - heat exchange on the working media in external circulation loops. Despite the desire for a reduction of or even prevention of irreversibilities occurring in the process, in the real absorption chiller there is avery small or no influence on the irreversibilities. 2 CALCULATION OF EXERGY FLOWS The calculation of exergy flows is performed using the data from Table 1 and any available literature ([1] and [4]) with a determination of specific flow exergy in labelled positions of the chiller (Fig. 1 and 2). The specific flow exergy tells us how much work has been produced with the unit of mass flow by reversible and mutual interaction with the environment [2]. The specific flow exergy in the device’s labelled positions, in the cooling and heating cycle is determined by the equation: e = h - h - T .(s - s) (1). Za določitev vrednosti specifične eksergije v toplotnem kompresorju običajno uporabimo eksergijski diagram na sliki 3. Usually we use the exergy diagram (Fig. 3) to determine values of specific flow exergy in the thermal compressor. stran 519 V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows Preglednica 1. Osnovni podatki absorpcijske hladilne naprave Table 1. Basic data for the absorption chiller___________________________ Osnovni podatki prenosnikov toplote Basic data for the heat exchangers________________________ k.AEV = 11,9 kW/K___________k.AHX = 2,0 kW/K k.AC = 17,9 kW/K___________k.AA = 6,1 kW/K k.AGen = 8,5 kW/K____________________________________ masni pretok zunanjega obtoka mass flow in the external circuits: kondenzator in absorber qm,k = qm a = 4,2 kg/s condenser and absorber________________ ____________ uparjalnik qmup = 2,3 kg/s evaporator___________________________ generator qm,gen = 3,2 kg/s generator____________________________ koncentrirana raztopina \qmrr = qm1 = 0,45 kg/s with coolant-rich solution___________I ___________ (a) Kondenzator (a) Condenser (b) Generator (b) Generator (c) Uparjalnik (c) Evaporator (d) Absorber (d) Absorber (e) Izmenjevalnik toplote (e) Solution heat exchanger (f) Dušilni ventil 2 (f) Throttle valve 2 (g) Črpalka raztopine (g) Solution pump (h) Dušilni ventil 1 (h) Throttle valve 1 Sl. 2. Diagram pretoka eksergij v absorpcijski hladilni napravi Fig. 2. Exergy flow diagram in the absorption chiller _____00 8 SnnsjtaleJUMllfiGC] I ^BSfirTMlliC | stran 520 i V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows Sl. 3. Diagram ex,x delovne snovi LiBr/H2O [5] Fig. 3. ex,x diagram for working media LiBr/H2O [5] Negativni predznak specifične eksergije dobimo v primeru, ko se povečuje entropija toka snovi pri hkratnem padcu tlaka pod tlak okolice [2]. To se pojavi, v analiziranem primeru, za stanja v točki 9 in 10 (slika 1). Rezultati preračuna eksergijskih tokov absorpcijske hladilne naprave so podani v preglednicah 2 in 3, kjer oznake posameznih veličin ustrezajo oznakam na sliki 1 in diagramu eksergijskih tokov na sliki 2. A negative sign for specific flow exergy was obtained for the case where the entropy of flow increased with a simultaneous pressure drop below the value of the environment’s pressure [2]. This occured, in our case, for positions 9 and 10 (Fig. 1). The calculated results of exergy flows in the absorption chiller are given in Table 1 and Table 2, where the thermodynamic properties correspond to those named in Figure 1 and exergy flow diagram in Figure 2. Preglednica 2. Vrednosti specifične eksergije, masnega pretoka in temperature v posameznih točkah naprave Table 2. Values of mass flow, temperature and specific flow exergy in the labelled position of the absorption chiller Masni pretok Mass flow Temperatura Temperature Specifična eksergija Specific exergy qm.i kg/s t °C ex.i kJ/kg 1 0,4500 41,9 48,3000 2 0,4500 41,9 48,3000 3 0,4500 71,1 120,7000 4 0,4216 85,7 131,0500 5 0,4216 52,5 69,0000 6 0,4216 50,3 62,1000 7 0,0287 76,2 102,6000 8 0,0287 31,5 0,8369 9 0,0287 2,1 - 5,1740 10 11 12 13 14 15 16 17 18 Masni pretok Mass flow qm.i kg/s 0,0287 3,2000 3,2000 4,2000 4,2000 4,2000 4,2000 2,3000 Temperatura Temperature t____°_C 2,1 29,3 34,5 25,0 29,3 12,0 2,3000 5,0 1,7700 Specifična eksergija Specific exergy ex.i kJ/kg -155,1000 95,0 34,6500 88,3 29,1200 0,5079 1,4550 0,0737 0,5079 0,4333 stran 521 glTMDDC V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows Preglednica 3. Vrednosti eksergijskih in anergijskih tokov enostopenjske absorpcijske hladilne naprave Table 3. Values of exergy and anergy flows in the single-stage absorption chiller Sestavina naprave Component of device kondenzator condenser absorber -85,87 absorber 67,7200 prenosnik toplote heat exchanger generator uparjalnik evaporator dušilni ventil - 1 throttle valve - 1 dušilni ventil - 2 throttle valve - 2 črpalka raztopine solution pump Eksergijski tok Exergy flow Sestavina Component . Exi kW 3,1200 6,6100 generator 13,5700 3,7900 0,001033 Anergijski tok Anergy flow . An kW -68,47 71,41 Zunanji obtok External loop Eksergijski tok Exergy flow D . Exi kW 1,54 3,59 6,77 - - 75,48 -18,4 75,48 3,05 Anergijski tok Anergy flow D . An kW 69,73 82,98 71,41 0,11 - - 0,85 - - 2.1 Razlaga rezultatov Splošno je znano, da se pri termodinamični analizi toplotnih procesov odločamo za eksergijsko bolj varčne naprave. Med naštetimi vrstami nepovračljivosti, ki se pojavljajo v napravi (sl. 2), se izkaže, da se največje nepovračljivosti pojavljajo v generatorju in absorberju (pregl. 3), kjer se namreč poleg nepovračljivosti pri prenosu toplote pojavljajo še nepovračljivosti zaradi mešanja delovne snovi. Na sliki 1 opažamo nasprotno smer toplotnega in eksergijskega toka v uparjalniku. Ta pojav je specifičen v tem, da se telesom, katerih temperatura je pod temperaturo okolice in se jim toplota odvaja, vrednost eksergije veča in nasprotno [6]. Prav zaradi tega se lahko utemeljeno sklepa, da lahko termodinamično pravilno zapišemo izkoristek vložene energije v napravo, v kateri hkrati potekata gretje in hlajenje, samo z eksergijskim izkoristkom. Za absorpcijsko hladilno napravo, pri kateri izkoriščamo samo hlad, lahko določimo eksergijski izkoristek z enačbo: DExUP yA AHN DE xGEN +Pp 2.1 Comments on the results It is a well-known fact, that with a thermo-dynamic analysis of thermal processes we are concentrating on the more exergy-saving type of plants. The named forms of irreversibilities, which occurred in the device – Figure 2, become obvious according to the presented analysis, because the greatest irreversibilities occured in the generator and absorber (Table 3). Besides the irreversibilities in the heat transfer, irreversibilities due to the mixture processes were also present. In Figure 1 we can see the opposite directions of energy and exergy flows by evaporator. This phenomenon is specific for the systems (bodies) whose temperature are below the surrounding’s temperature and whilst they are rejecting heat (being cooled), their exergy value is growing and vice versa [6]. Therefore, this brings us to the using conclusion that thermodynamics is the only correct way to express the efficiency of consumed energy in the device where heating and cooling are simultaneously performed only with exergy efficiency. For the absorption chiller, where we utilize only cooling, we can determine the exergy efficiency using the following equation: 3, 05 (2). 18,4 0,166 V primeru, da poleg hladu izkoriščamo še oddano toploto kondenzatorja in absorberja (npr. segrevanje sanitarne vode), lahko eksergijski izkoristek absorpcijske hladilne naprave določimo z enačbo: yA . .. DEx +DEx +DEx 3,59+1,54+3,05 In the case where we also utilize rejected heat from the absorber and the condenser, we can determine the exergy efficiency with the following equation: AHN DE xGEN +Pp 18,4 0, 445 (3). 00-8 VH^tTPsDDIK stran 522 - - V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows Moč potrebne črpalke se zaradi doslednosti definicije v enačbah (2) in (3) zapiše, vendar se zaradi majhne vrednosti, (pregl. 3) v računu ne upošteva. 3 SKLEP Prednost sorpcijskih hladilnih naprav, v obravnavanem primeru absorpcijskih hladilnih naprav, pred kompresorskimi hladilnimi napravami je v možnosti uporabe eksergijsko revne odpadne toplote in rabe alternativnih energijskih virov. Kompresorske hladilne naprave so sicer energetsko učinkovitejše in manjše, vendar eksergijsko manj učinkovite in porabljajo čisto eksergijo [7]. Za pogon absorpcijskih hladilnih naprav se lahko uporablja tudi odpadna toplota postroja soproizvodnje. Postroj sočasne proizvodnje električne energije in toplote ter hladu imenujemo trigeneracijski postroj [8]. Pri trigeneracijskih postrojih je zaželeno, da ima absorpcijska hladilna naprava kar se da velik eksergijski izkoristek in s tem dosežemo večji eksergijski izkoristek celotnega trigeneracijskega postroja [8]. We have to consider the power of the pump to obtain the correct definitions, equation (2) and (3), which due to its small value, is unimportant. 3 CONCLUSION The advantage of sorption chillers, in our case absorption chillers, in comparison to compressor chillers is in utilizing low exergy, rejected heat and in the use of alternative energy sources. Compressor chillers have a higher energy efficiency and are more compact, but they are less exergy efficient and utilize pure exergy [7]. To drive the absorption chiller we can also utilize the rejected heat from the cogeneration plant. This kind of plant, with simultaneous production of heat, electricity and cooling is also called the trigeneration system [8]. In the trigeneration plant all the requirements are present, the absorption chiller has the highest possible exergy efficiency, which enables it to achieve higher exergy efficiency in the whole trigeneration plant [8]. 4 OZNAKE 4 SYMBOLS anergijski tok . An W anergy flow specifična eksergija snovnega toka ex J/kg mass flow specific exergy energijski tok Ex W exergy flow specifična entalpija H J/kg specific enthalpy moč P W power masni pretok q kg/s mass flow temperatura T K temperature x % mass ratio eksergijski izkoristek y % exergy efficiency Indeksi: Subscripts: absorber A absorber absorbcijska hladilna naprava AHN absorption chiller generator Gen generator kondenzator K condenser referenčno stanje okolice o reference state črpalka p pump prenosnik toplote PT heat exchanger uparjalnik UP evaporator 5 LITERATURA 5 REFERENCES [1] Herold, E.K., R. Radermacher, S.A. Klein (1996) Absorption chillers and heat pumps. New York, CRC Press. [2] Obersnu, T. (1991) Strojno hlajenje in gretje. Ljubljana, Tehniška založba Slovenije. [3] Bošnjakovič, F. (1986) Nauka o toplini - III dio. Zagreb, Tehnička knjiga. [4] Hellmann, H.-M., F. Ziegler (1998) A simple method for modeling the operating characteristics of absorption chillers, Eurotherm No 59,7/1998, Nancy-France. gfin^OtJJlMISCSD 00-8 stran 523 |^BSSITIMIGC V. Vasi} - J. Krope - D. Gori~anec: Analiza eksergijskih tokov - Ana Analysis of Exergy Flows [5] Karavan, S.V., I.I. Orehov, E.A. Gavrilov (1986) Ental’pijnnaja i eksergetičeskaja diagrammy vodjanogo rastvora bromistogo litija, No.11,4 K45, Pisčevaja promisljenost’. [6] Voprosy termodinamičeskogo analiza - eksergetičeskij metod (1965) Mir, Moskva. [7] Poredoš, A. (1994) Eksergijska analiza parnih in sorpcijskih hladilnih procesov. Ljubljana, Strojniki vestnik (40), 7+8. [8] Vasic, V., D. Goričanec, D. Kosič (1999) Eksergijska analiza trigeneracionih sistema. Kongres KGH (33), Beograd –Jugoslavija. Naslova avtorjev: mag. Vasilije Vasic prof.dr. Jurij Krope doc.dr. Darko Goričanec Fakulteta za kemijo in kemijsko tehnologijo Univerze v Mariboru Smetanova 17 2000 Maribor Authors’ Address: Mag. Vasilije Vasic Prof.Dr. Jurij Krope Doc.Dr. Darko Goričanec Faculty of Chemistry and Chemical Engineering University of Maribor Smetanova 17 2000 Maribor, Slovenia Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 00-8 VH^tTPsDDIK stran 524 © Strojni{ki vestnik 46(2000)8,525-531 © Journal of Mechanical Engineering 46(2000)8,525-531 ISSN 0039-2480 ISSN 0039-2480 UDK 532.5:621.644:697.4 UDC 532.5:621.644:697.4 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Zmanj{anje tla~nih izgub v vro~evodnih cevnih mre`ah The Reduction of Friction Losses in District-Heating Pipelines Andrej Krope - Jurij Krope - Igor Ti~ar V prispevku je predstavljen vpliv kationskih površinsko aktivnih dodatkov na zmanjšanje intenzivnosti turbulence v ceveh primarnih vročevodnih mrež sistemov za daljinsko ogrevanje. Že zelo majhne količine dodatkov vroči vodi, povzročijo znatno zmanjšanje odpora pri pretoku po ceveh in zato manjše izgube tlaka, kar vodi do manjše potrebne moči črpalk, znižanja črpalnih stroškov, povečanja zmogljivosti, zmanjšanja stroškov plina za ogrevanje vode in zmanjšanja toplotnih izgub. Pri načrtovanju in izgradnji novih vročevodnih mrež lahko uporabljamo cevi z manjšimi premeri in tako znatno znižamo investicijske stroške. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: pretok fluida, izgube tlačne, dodatki, sistemi toplovodni) In the paper the impact of cationic surfactant additives on reducing the turbulence intensity in the hot-water pipelines of district heating systems is presented. With small amounts of cationic surfactants in district-heating water the friction losses in pipelines can be reduced significantly. Because of this effect the pressure drops are decreased what leads to reductions in pump energy, pumping costs, costs of gas for heating the supply water, heat losses and to an increase in the heat capacity. New district-heating networks can be designed with smaller pipe diameters and so investment costs can be reduced significantly by applying friction-reducing additives. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: fluid flow, pressure drops, additives, heating pipelines) 0 UVOD Zmanjšanje zalog primarnih goriv in s tem v zvezi varčevanje z energijo terja na področju toplotne tehnike iskanje novih tehnično-znanstvenih spoznanj, kar je v zadnjem času pomembna tema številnih državnih in mednarodnih raziskovalnih projektov. Težišče raziskav temelji na boljšem izkoriščanju primarne energije. Energetski sistemi za daljinsko ogrevanje zagotavljajo prihranke pri porabi primarne energije in ekološko sprejemljivo oskrbo s toplotno energijo [1]. Z ekonomskega vidika gre v primeru daljinskega ogrevanja za nasprotje med nizkimi stroški proizvodnje toplotne energije in relativno visokimi prenosnimi in razdeljevalnimi stroški. Večino stroškov, povezanih s sistemi daljinskega ogrevanja pomenijo naložbe v cevno mrežo ter stroški črpanja. Zaradi tega so sistemi daljinskega ogrevanja cenovno razmeroma ugodni le pri majhnih pretočnih razdaljah. Ena od možnosti za izboljšanje učinkovitosti in gospodarnosti takšnih sistemov je dodajanje snovi za 0 INTRODUCTION Decrease of primary energy supplies and in this connection saving with energy demands investigations for new technical-scientific cognition in the field of heat engineering, what is an important topic of numerous national and international research projects particularly in recent years. The centre of this researches is more rational exploitation of primary energy. District-heating systems ensure savings by consumption of primary energy and ecological heat-energy supply [1]. From the economic point of view there is a contradiction between low heat-generation costs and relatively high transport and distribution costs of district heat. The investments in pipelines and pumps, together with the pumping costs, form a major cost item of district-heating systems. For this reason the costs for such systems are relatively favourable only at short transport distances. One of the possibilities to improve effectiveness and economic viability of district-heating systems is applica- stran 525 |^BSSIrlMlGC A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses zmanjšanje odpora pri pretoku tekočin. Na ta način lahko znatno zmanjšamo tlačne izgube, povečamo pretok in s tem prenos toplotne energije, kar vodi do občutnega znižanja naložb v cevi in črpalke ter znižanja stroškov električne energije, ki je potrebna za pogon črpalk. Zmanjšanje tlačnih izgub se kaže tudi v primernejši rabi primarne energije in nižji obremenitvi okolja. Vpliv majhnih količin dodatkov vodi na odpor pri pretoku tekočin in padec tlaka v ravni cevi je že leta 1948 odkril Toms [2]. Od tedaj je bilo izvedenih že na stotine preskusov, ki so potrdili takratno odkritje. Značilnosti tega pojava so naslednje: - pri pretoku vode v ceveh je mogoče z dodatkom raztopine dodatka koncentracije 5 ppm zmanjšati odpor za 70 %, - večje znižanje odpora se pojavlja le pri turbulentnem toku, - z dodatkom raztopine dodatka je mogoče povečati pretok za 30 %, - raztopine dodatkov so učinkovitejše pri ceveh manjšega premera. V preteklosti so za znižanje odpora uporabljali različne polimerne dodatke z veliko molekulsko maso, vendar so se ti izkazali za manj uporabne zaradi nepovračljive razgradnje, ki se pojavi pri velikih strižnih silah. Danes se za znižanje odpora v vročevodnih cevnih sistemih uporabljajo kationski površinsko aktivni dodatki majhnih molekulskih mas, ki povzročajo znižanje tlačnih izgub že v zelo majhnih koncentracijah in imajo povračljivo strukturo. 1 DELOVANJE KATIONSKIH POVRŠINSKO AKTIVNIH DODATKOV Učinek zmanjšanja viskoznosti in s tem odpora pri pretoku tekočin, ki ga povzročajo vodne raztopine dodatkov, temelji na zmanjšanju intenzivnosti turbulence in ga lahko pojasnimo s tvorbo in oblikovanjem micelijev Površinsko aktivni dodatki so nizkomole-kularne snovi z majhno kemijsko aktivnostjo in nizko topnostjo, ki so sestavljene iz hidrofilnega in hidrofobnega dela [3]. Kadar so takšne molekule v vodi ali v topilu, ki ima podobne lastnosti kakor voda, se pod določenimi pogoji združejejo v združbe, ki jih imenujemo miceliji. Miceliji so aglomerati nekaj sto molekul in lahko imajo različne oblike; lahko so okrogli, palični ali pa ploščati. Potrebni pogoj za zmanjšanje odpora so palični miceliji. Kritično micelarno koncentracijo, nad katero se molekule dodatka združujejo v micelije, prikazuje slika 1. Če je v vodni raztopini dodatka presežena koncentracija CMC1, pride do tvorbe krogelnih micelijev s premerom približno dvakratne dolžine posamezne molekule. Ta koncentracija je le malo odvisna od temperature. Če ^BSfiTTMlCC | stran 526 tion of friction-reducing additives in hot-water supply pipelines. In this way pressure drops can be significantly reduced and the flow rate can be increased enabling a reduction in the investment in pipelines and pumps and savings in the costs of electrical energy used for drive of pumps. A reduction of friction loss is also shown to be more rational consumption of primary energy and results in a impact on the environment. As early as 1948 Toms [2] reported on friction loss and pressure drop when minute amounts of soluble polymer additive where added to water flowing through a straight pipeline. Since then, hundreds of experiments have confirmed his initial findings. The essential features of this phenomenon are as follows: - the friction loss of water flow in pipelines can be reduced as much as 70% with additives in concentrations as low as 5 ppm, - significant reductions in friction loss occur only for turbulent flow, - additives can increase the flow rate by 30%, - additive solutions are more effective on small pipelines than on large ones. In the past a variety of polymer-based additives with high molecular weight have been used for reducing the friction losses, however, they have proved as less applicable because of their irreversible degradation which occurs at high values of shear stress. Nowadays, low molecular cationic surfactant additives, which effect on reduction of pressure drops already in small quantities and have reversible structure, are used for drag reduction in hot-water-pipe systems. 1 OPERATING PRINCIPLE OF SURFACTANTS The phenomenon of friction reduction with surfactants in aqueous solutions is based on the decrease of the turbulence intensity and can be explained with the formation and the shape of micelles. Surfactants are low-molecular-weight substances with low chemical activity and low solubility, but great interfacial activity. The molecules consist of a hydrophilic group and a hydrophobic part [3]. Under certain conditions the surfactant monomers form micelles in aqueous solutions. Micelles are clusters of approximately a hundred surfactant molecules and can take any of a variety of shapes, such as spheres, bars or disks. The presence of rod-like micelles is considered to be a necessary condition for the friction-reducing effect. Critical micelle concentrations, above which surfactant molecules form micelles, are shown in Figure 1. When the critical micelle concentration (CMC1) in an aqueous solution is exceeded the surfactants form spherical micelles. This concentration is almost temperature independent. If the concentration is increased still further, the A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses se koncentracija še naprej povečuje, se število molekul dodatka na micelij povečuje, dokler ni celotna prostornina micelija popolnoma izpolnjena z ogljikovimi verigami. Ko je presežena koncentracija CMC, tvorijo dodatki palične micelije, ker je takšna prostorska oblika energijsko ugodnejša. Dolžina paličnih micelijev se povečuje z naraščajočo koncentracijo. Kritična koncentacija CMC2 je močno odvisna od temperature. number of surfactant molecules per micelle will increase until the micelle volume is completely filled with carbon chains. When the second critical micelle concentration (CMC2) is exceeded the surfactants form rod-like micelles, because these boundary faces are more energetically favourable. The length of bar-shaped micelles increases with increasing concentration. The CMC2 concentration is strongly temperature dependent. tpalični miceliji i rod-like micelles .CMC; krogelni miceliji spherical micelles temperatura temperature Sl. 1. Kritična micelarna koncentracija [3] Fig. 1. Critical micelle concentrations [3] Vodne raztopine dodatkov, ki tvorijo krogelne micelije se obnašajo podobno kakor voda, viskoznost takih raztopin je včasih celo večja od viskoznosti čiste vode in zato ne povzročajo učinka znižaja odpora pri pretoku tekočine. Pri koncentracijah, večjih od CMC2, pa se v raztopini dodatka oblikujejo palični miceliji, ki kažejo viskoelastično obnašanje. Takse celice micelijev se zaradi turbulentnega toka in strižnih sil usmerjajo v smeri toka in tvorijo viskoelastično prostorsko mrežo, ki razširi prehodni sloj in zmanjša turbulentno jedro glavnega toka (sl. 2). V palični micelij rod-like micelles Aqueous surfactant solutions that form spherical micelles behave in the same way as the water, at high concentrations the viscosity becomes somewhat higher than that of the water, so this clusters do not perform friction-reducing effect. At concentrations that are higher than CMC2, the surfactant solutions in which rod-like micelles have formed exhibit a favourable viscoelastic behaviour. Such cells become oriented by the pulse loads of turbulent flow and form a permanently oriented viscoelastic network which expands the buffer layer and reduces the layer of turbulent main-stream flow (Fig. 2). Wpr strižne sile shear stress Sl. 2. Viskoelastična mreža in usmeritev paličnih micelijev zaradi delovanja strižnih sil [3] Fig. 2. Viscoelastic network, orientation of micelles, shear induced structure [3] stran 527 |^BSSITIMIGC A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses Pri koncentracijah okoli CMC se oblikuje le nekaj relativno velikih micelijev, ki pa so le omejeno sposobni oblikovati usmerjene mreže, zato je njihov vpliv na znižanje odpora majhen. Za zadovoljivo znižanje je zato potrebna večja koncentracija, ki povzroči trajno usmerjene viskoelastične mreže, ki dušijo razvijanje turbulentnih vrtincev in tako povzročajo laminarni tok. Funkcionalno odvisnost vodnih raztopin kationskih površinsko aktivnih dodatkov od Reynoldsovega števila prikazuje slika 3, na kateri opazimo 4 različna področja [4]: => => => Področje I: v laminarnem področju toka z majhnimi strižnimi silami ali brez njih oblikujejo palični miceliji prostorsko mrežo z elektrostatskim odbojem, ki je posledica njihovega površinskega naboja, in v njej zasedejo energetsko ugodna mesta. V tem stanju se raztopine površinsko aktivnih dodatkov obnašajo kot newtonske tekočine. Področje II: povečanje strižnih sil in turbulentni tok vplivata na usmerjanje micelijev in oblikovanje viskoelastične mreže, kar povzroča laminaren tok. V tem stanju se raztopine površinsko aktivnih dodatkov obnašajo kot pseudoplastične tekočine. Področje III: nadaljnje povečevanje strižnih sil vpliva na povečanje učinka zniževanja odpora. Miceliji so zmožni sprejeti več energije, ker deformiranje in raztezanje mreže povzroča sile, ki delujejo proti turbulentnemu vrtinčastemu gibanju in zato manjšajo oddajo energije. V tem področju je, ob uporabi dodatka, katerega delovno območje se ujema z obratovalnimi razmerami v sistemu daljinskega ogrevanja, učinek znižanja odpora neodvisen od koncentracije vodne raztopine dodatka. Raztopine dodatkov se tudi v tem področju obnašajo pseudoplastično, vrsto toka, ki se pojavi v takšnih razmerah pa imenujemo pseudolaminarni tok. If the concentration is only just above CMC, then only few relatively large micelles will be formed. These micelles are not well capable of forming an oriented network, which is why their friction effect is only small. Therefore, for a significant reduction of friction losses a higher concentration is required. These concentrations generate permanently oriented viscoelastic networks which suppress the formation of turbulent whirls and produce a laminar flow in this way. The functional relationsip between surfactant-solution behaviour and Reynolds number is shown in Figure 3, where we can see four different ranges [4]: => range I: In the laminar region of flow with little or no shear stress the rod-like micelles form a spatial network with the electrostatic repulsion caused by their surface charge, in which they occupy energetically favourable positions. In this state the surfactant solution shows Newtonian behaviour. => range II: A rise of shear stress and turbulent flow lead to orientation of the rod-like micelles and formation of the viscoelastic network what causes laminar flow. In this range the surfactant solution shows pseudoplastic flow behaviour. => range III: A further rise in shear stress leads to an increase in friction reduction. In this range the maximum reduction of friction losses appears. Micelles are able to incorporate more energy because deforming and stretching causes reset forces which act against the turbulent fluctuation movement and therefore reduce the energy dissipation. In this range pseudoplastic behaviour exist as well and this flow condition is known as pseudolaminar flow I Prandtl-Colebrookova enačba Prandtl-Colebrooke equation voda water Hagen- Poiseuillejevaj enačba Hagen- Poiseuille equation področje I range I raztopina dodatka surfactant solution področje IV range IV log Re Sl. 3. Darcyjev koeficient linijskih izgub v odvisnosti od Reynoldsovega števila za vodne raztopine dodatkov [4] Fig. 3. Darcy’s friction coefficient with its dependence on the Reynolds number for aqueous surfactant solution [4] 00-8 grin^sfcflMiecsD ^BSfiTTMlCC | stran 528 A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses => Področje IV: zelo visoke strižne sile, ki jih povzroča povečana hitrost toka povzročijo razpad viskoelastične micelarne mreže in s tem konec vpliva dodatkov na znižanje odpora. Značilna krivulja raztopine dodatka doseže krivuljo vode. V tem področju nastane celovit turbulentni tok, raztopine površinsko aktivnih dodatkov se ponovno obnašajo kot newtonske tekočine. Hkrati s pozitivnim učinkom znižanja odpora se pri uporabi dodatkov, zaradi spremenjenih pretočnih razmer (newtonsko obnašanje tekočine zamenja pseudoplastično) pojavijo tudi negativni učinki: to so zmanjšanje prenosa toplote, korozija in onesnaževanje okolja [1]. Problem zmanjšanega prenosa toplote rešujemo z modeliranjem vrste in lokacije prenosnikov toplote ter tako, da v menjalnike vstavljamo pregrade, ki povečujejo turbulenco in s tem prenos toplote. Novejše raziskave so pokazale, da kombinirani površinsko aktivni dodatki s tržnimi imeni Habon G / NaSal, Obon G / NaSal in Dobon G / NaSal ne kažejo nobenega vpliva na korozijo materialov, ki se uporabljajo v sistemih daljinskega ogrevanja. Problem strupenosti dodatkov in s tem povezanega onesnaževanja okolja rešujemo tako, da jih uporabljamo le v zaprtih sistemih s posredno povezavo obrata za proizvodnjo toplote in porabnikov prek toplotnih postaj in sekundarne mreže. 2 KOMBINIRANI KATIONSKI POVRŠINSKO AKTIVNI DODATKI Najboljše rezultate dosežemo s površinsko aktivnimi dodatki Habon G, Obon G in Dobon G v kombinaciji s snovjo NaSal, ki zagotavlja širše temperaturno področje delovanja. Kemijsko strukturo omenjenih dodatkov, ki so uporabni pri koncentracijah do 1500 utežnih ppm in hitrostih toka do 4 m/s, prikazuje slika 4. CH | CH2n+- N - CH3 (C2H4O)12H n-Alcyldimethylpolyoxethylammonium - Cation => range IV Very high shear rates finally affect the destruction of the viscoelastic micelle network so that the friction-reducing effect disappears and the characteristic surfactant solution curve approaches that of water. In this case a fully developed turbulent flow appears, which again shows Newtonian behaviour. As well as the positive effects of drag reduction, negative effects due to the change in flow behaviour (pseudoplastic behaviour instead of Newtonian) [1] like heat-transfer reduction, corrosion and contamination of environment also occur. The phenomenon of radial turbulence and the associated reduction of heat transfer in heat exchangers can be solved by installing turbulence-increasing obstacles inside the heat exchangers to improve the heat-transmission properties. Some new investigations have shown that combined cationic surfactants with the trade names Habon G / NaSal, Obon G / NaSal and Dobon G / NaSal do not show any impact on the corrosion rates of materials which are built in district-heating systems. The problem of contamination and pollution of environment can be solved by only using surfactants in closed transport systems with an indirectly connected heat-generation plant and consumer systems. This can be achieved with the installation of heat-transmission stations and secondary hot-water-pipe network. 2 COMBINED CATIONIC SURFACTANTS The best results by reduction of friction losses in hot-water pipelines can be achieved with the cationic surfactant substances Habon G, Obon G and Dobon G in combination with the additional counter-ion NaSal, which ensures extended temperature range of operation. The chemical structure of above-mentioned surfactants, which can be used by concentrations up to 1500 wppm and flow velocities up to 4 m/s is shown in Figure 4. /COO .- ^COO :oioi. ®C OH OH 3-hydroxy-2-naphthoate Salicylate Sl. 4 Kemijska struktura površinsko aktivnih dodatkov [3] Fig. 4. Chemical structure of cationic surfactants [3] Temperaturno področje, v katerem omenjeni dodatki zagotavljajo znižanje odpora, je odvisno od števila ogljikovih atomov: n = 16 (tržno ime Habon G / NaSal): od 25 do 105 °C n = 18 (tržno ime Obon G / NaSal): od 35 do 120 °C n = 22 (tržno ime Dobon G / NaSal): od 45 do 140 °C The temperature range for which these surfactants show a friction-reduction effect depends on number of carbon atoms: n = 16 (trade name Habon G / NaSal): from 25 to 105 °C n = 18 (trade name Obon G / NaSal): from 35 to 120 °C n = 22 (trade name Dobon G / NaSal): from 45 to 140 °C stran 529 |^BSSITIMIGC A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses 3 DOLOČITEV EMPIRIČNE ENAČBE DARCYJEVEGA KOEFICIENTA TORNIH IZGUB Dodatek kombiniranega dodatka Dobon G / NaSal v vročevodno cevno mrežo zniža odpor pri pretoku in povzroči zmanjšanje izgube tlaka. To znižanje odpora upoštevamo z enačbo, ki smo jo razvili v Laboratoriju za toplotno tehniko na Fakulteti za strojništvo Univerze v Mariboru [5]. Na temelju eksperimentalnih podatkov smo, z uporabo računalniškega programa Matlab in funkcije FMINS, ki izvaja Nelder-Meadov simpleks algoritem, določili odvisnost koeficienta tornih izgub (l) zaradi dodanega dodatka od Reynoldsovega števila (Re) v obliki potence funkcije drugega reda z dvema linearnima in dvema nelinearnima koeficientoma v obliki (1): 3 DETERMINATION OF THE EMPIRICAL EQUATION OF DARCY’S FRICTION COEFFICIENT The addition of the combined surfactant Dobon G / NaSal to hot-water-pipe network decreases the friction losses and reduce pressure drops in pipelines. This reduction of friction can be considered with the equation, which has been developed in our Laboratory for Heat Engineering at the University of Maribor, Faculty of Mechanical Engineering [5]. On the basis of experimental data and the help of The Matlab computer software with the FMINS function which performs Nelder-Meadov’s simplex algorithm, the relationship between Darcy’s friction coefficient (l) and Reynolds number (Re) has been determined in form of a power function of the second grade with two linear and two non-linear coefficients (1): /1 = 0,17442 • Re- 0,00603 • Re0, (1). 4 SKLEP 4 CONCLUSION Uporaba dodatkov v sistemih daljinskega ogrevanja zagotavlja izboljšanje učinkovitosti in gospodarnosti obratovanja. Učinek zmanjšanja viskoznosti in s tem odpora, ki ga povzročajo vodne raztopine kationskih površinsko aktivnih dodatkov temelji na zmanjšanju turbulence in ga lahko pojasnimo s tvorbo in oblikovanjem paličnih micelijev Pri koncentracijah, večjih od kritične koncentracije CMC, se v raztopini dodatka oblikujejo palični miceliji, ki kažejo viskoelastično obnašanje. Takšne celice micelijev se zaradi turbulentnega toka in strižnih sil usmerjajo v smeri toka in oblikujejo viskoelastično prostorsko mrežo, ki razširi prehodni sloj in zmanjša turbulentno jedro glavnega toka. Zmanjšanje odpora pri pretoku tekočin ima za posledico zmanjšanje tlačnih izgub in zato znižanje stroškov električne energije za pogon črpalk, povečanje kapacitete, manjše stroške plina za ogrevanje vode in manjše toplotne izgube. Znižanje odpora pa se kaže tudi v manjši potrebni moči črpalk in nižji vrednosti naložbe v cevi z manjšimi nazivnimi premeri pri gradnji novega omrežja [6], kar omogoča oskrbo s toploto tudi v primeru večjih pretočnih razdalj. Treba pa je poudariti tudi pozitiven vpliv uporabe dodatkov na smotrno rabo energije in zaradi tega na manjšo obremenitev okolja. The use of surfactants in district-heating systems results in an improvement in the system’s operation. The effect of friction reduction, which is a result of the surfactants added to hot-water supply, is based on reduction of turbulence intensity and can be explained by the formation of rod-like micelles. At concentrations higher than the critical micelle concentration (CMC2) the surfactants form rod-like micelles which show viscoelastic behaviour. Such micelle cells become oriented and form viscoelastic network because of the turbulent flow and shear stress. This shear-induced state expands the buffer layer and reduces the layer of turbulent main-stream flow. The reduction of friction losses and the resulting reduced pressure drops lower the electrical energy costs for pump driving, the gas cost for heating the supply water and the heat losses while increasing the heat capacity. The reduction of friction is also reflected in a decreased pump energy and lower investment costs for hot-water pipelines, as new networks can be designed with smaller pipe diameters [6], or the maximum economic transport length can be increased. Likewise the positive effect of surfactant application is shown in more rational consumption of energy and consecutively lower charge of environment, what has to be mentioned, too. 5 LITERATURA 5 REFERENCES [1] Krope, A. (1999) Optimiranje cevnih mrež z uporabo aditivov Magistrsko delo (Master’s thesis), Faculty of Chemistry and Chemical Engineering, Maribor, Slovenija [2] Roberson, J.A., C.T Crowe (1997) Engineering fluid mechanics, Sixth Edition. John Wiley & Sons, Inc., New York, USA. 00-8 grin^sfcflMiecsD ^BSfiTTMlCC | stran 530 A.Krope - J. Krope - I. Ti~ar: Zmanj{anje tla~nih izgub - The Reduction of Friction Losses [3] de Groot, M.C., E.A. Kievit (1996) The effects of surfactants on domestic heat exchangers for hot water supply and heat flow meters in D/H systems. Technical University of Delft, Mechanical & Maritime Engineering, Thermal Power Engineering, NOVEM, Sittard, The Netherlands. [4] Weinspach, P.-M. (1996) Improving the heat transmission properties of tube bundle heat exchangers by installing obstacles inside the pipes; D1: Investigations of heat transfer and pressure drop. Thermische Verfahrenstechnik GmbH, Dortmund, Germany. [5] Rupnik, A. (1997) Ekonomičnost uporabe aditivov v toplotnih sistemih daljinskega ogrevanja. Magistrsko delo (Master’s thesis), Faculty of Chemistry and Chemical Engineering, Maribor, Slovenija. [6] Krope, A, J. Krope, D. Goricanec: Optimal design of district heating networks operating with drag reducing additives. Proceedings of the IASTED International Conference: Applied Modelling and Simulation, Cairns, Australia, 1999. Naslovi avtorjev: mag. Andrej Krope Fakulteta za strojništvo Univerze v Mariboru Smetanova 17 2000 Maribor Authors’ Addresses: Mag. Andrej Krope Faculty of Mechanical Eng. University of Maribor Smetanova 17 2000 Maribor, Slovenia prof.dr. Jurij Krope Fakulteta za kemijo in kemijsko tehnologijo Univerze v Mariboru Smetanova 17 2000 Maribor Prof.Dr. Jurij Krope Faculty of Chemistry and Chemical Engineering University of Maribor Smetanova 17 2000 Maribor, Slovenia profdr. Igor Tičar Fakulteta za elektrotehniko, računalništvo in informatiko Univerze v Mariboru Smetanova 17 2000 Maribor Prof.Dr. Igor Tičar Faculty of Electrical Engineering and Computer Science University of Maribor Smetanova 17 2000 Maribor, Slovenia Prejeto: 15.8.2000 Received: Sprejeto: 10.11.2000 Accepted: stran 531 |^BSSIrlMlGC © Strojni{ki vestnik 46(2000)8,532-537 © Journal of Mechanical Engineering 46(2000)8,532-537 ISSN 0039-2480 ISSN 0039-2480 UDK 546.212:628.16.04/.09:66.06:537.84 UDC 546.212:628.16.04/.09:66.06:537.84 Pregledni znanstveni ~lanek (1.02) Review scientific paper (1.02) Spremenjeno kristaljenje vodnega kamna pri magnetni obdelavi vode Modified Scale Crystallization in Magnetic Water Treatment Andrej Pristovnik - Lucija ^repin{ek Lipu{ - Jurij Krope Magnetna obdelava vode (MOV) je alternativna metoda priprave napajalnih vod za nadzor vodnega kamna in prav tako postaja pomembna pri izboljšavah drugih tekočin, ki vsebujejo vodo. Govor je o učinkih naprav MOV, med njimi o spremenjenem kristaljenju vodnega kamna in spremenjeni stabilnosti vodnih disperzij s poudarkom na spremenjeni hidrataciji ionov in trdnih površin zaradi magnetne protonske resonance kot enega izmed možnih mehanizmov. Nadalje je predlagana pojasnitev pospešenega obarjanja aragonita. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: priprava vode, kristaljenje CaCO3, hidratacija ionska, magnetohidrodinamika) Magnetic water treatment (MWT) is an alternative method of supplied-water conditioning for scale control and is also important in the amelioration of other water-based fluids. The effects of MWT devices, such as the modified crystallization of the scale-forming components and modified stability of the dispersion are discussed with the emphasis on the modified hydration of ions and solid surfaces due to magnetic proton resonance as one of the possible mechanisms. In addition, a possible explanation for the accelerated arago-nite precipitation is proposed. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: water conditioning, crystallization, ion hydration, magnetohydrodynamic) 0 UVOD Nastajanje oblog vodnega kamna je pogosta in draga težava v mnogih industrijskih procesih, ki so napajani z naravnimi vodami. Do oblog na stenah naprav pride zaradi naravne prenasičenosti napajalne vode ali zaradi prenasičenja, ki se vzpostavi med ogrevanjem vode, padcem tlaka ali dvigom pH med samo obdelavo vode. Trde obloge zmanjšujejo pretočne zmogljivosti, povečujejo porabo električne energije črpalk in zahtevajo periodično čiščenje. MOV igra vse pomembnejšo vlogo alternativne metode pri pripravah industrijskih vod. Njene prednosti v primerjavi z znanimi kemijskimi metodami mehčanja vode so: nizki investicijski in obratovalni stroški, preprosta vgradnja, ohranjanje kakovosti vode (npr. organoleptičnih lastnosti) in prispevek k varstvu okolja. Pri napravah MOV, ki so bile dobro načrtovane za določen vodovodni sistem in dano sestavo vode [1], lahko pričakujemo veliko učinkovitost pri preprečevanju nastanka trdih oblog vodnega kamna, še posebej v ogrevanih in cirkuliranih vodovodnih sistemih. 0 INTRODUCTION The build up of scale deposit is a common and costly problem in many industrial processes which use natural water supplies. Deposits on the equipment walls result form the natural oversaturation of the supplied water or oversaturation caused by water heating, pressure drop or a pH increase during the water processing. The hard-scale deposit reduces water flow capacities, increases the electrical power consumption of pumps and reduces the heat exchanging capabilities of heated surfaces leading to higher operating costs and need to a periodically remove the scale. MWT is becoming increasingly important as an alternative method of industrial water conditioning. Low investment and operating costs, easy installation, water quality (i.e. organoleptic properties) and ecological benefits are some of the advantages over the well-known chemical methods used for water softening. MWT devices which are well designed for a particular water composition and industrial process [1], are very effective in preventing hard-scale formation, especially in heated- and circulated-water systems. VH^tTPsDDIK stran 532 A. Pristovnik - L.^. Lipu{ - J. Krope: Spremenjeno kristaljenje - Modified Scale Crystallization Prvi patent tovrstnih naprav je bil vknjižen v Belgiji leta 1945. Praktične izkušnje s to pionirsko napravo so dale zelo različne rezultate: od izjemne učinkovitosti, do popolne neuspešnosti [2]. Od leta 1960 so bili v nekdanji Sovjetski zvezi za nadzor vodnega kamna z veliko ekonomsko koristjo uporabljani močni elektromagneti [3], v USA pa so bile naprave MOV širše sprejete šele po letu 1975 ([4] in [5]). 1 UČINKI NAPRAV MOV NA NARAVNE IN INDUSTRIJSKE VODE Praktična uporaba naprav MOV je vse bolj razširjena na področju priprave vod za odstranjevanje ali preprečevanje vodnega kamna, prodira pa tudi na nova področja, to so obdelava cementa in goriva ([6] do [12]). V vseh teh primerih gre za obdelavo tekočine, ki vsebuje določen delež vode, da bi se izboljšale njene biokemijske ali fizikalno-kemijske lastnosti. Iz magnetno obdelane vode se vodni kamen tvorne komponente (predvsem CaCO3 v nizko-temperaturnih sistemih in CaSO4 v pregrevanih sistemih) namesto v obliki težko odstranljivih oblog obarja v suspendirani obliki. Kristali so drugačni po svoji obliki, velikosti in strukturi in so manj adhezivni. V primeru CaCO3 je bilo opaženo, da se lahko z magnetno obdelavo razmerje aragonit/kalcit bistveno zviša ([13] in [14]). Aragonit je kinetično ugodnejša kristalna faza, ki vsebuje slabo adhezivne kristale igličaste oblike. Kalcit je termodinamično ugodnejša kristalna faza, sestavljena iz rombičnih kristalov, ki lahko zaradi svoje velike adhezivnosti tvorijo trde, težko odstranljive obloge. Zvišano razmerje aragonit/kalcit delno pojasni obarjanje prašnatih oblog iz magnetno obdelane vode. Čeprav je kristaljenje iz magnetno obdelane vode zelo odvisno od same sestave vode in obratovalnih razmer, je v večini primerov opaženo obarjanje zmanjšanega števila kristalov CaCO3 ki so večji in imajo zvišan delež aragonita. Celo kristaljenje iz prenasičene mešanice statično magnetno obdelanih raztopin Na2CO3 in CaCl2 v dobro nadziranih laboratorijskih razmerah je dalo podobne rezultate [15]. 2 MEHANIZMI DELOVANJA NAPRAV MOV NA PROCESIRANO VODO Večdesetletne izkušnje na področju MOV so dale nekaj empiričnih osnov za načrtovanje magnetnih naprav, vendar pa še vedno ostaja odprto vprašanje mehanizem, ki bi natančno pojasnil, kako magnetno polje vpliva na obdelovani vodni sistem. Na temelju številnih eksperimentalnih in teoretskih poročil je sklepati, da mehanizem najverjetneje sestoji iz vzporednih, med seboj prepletenih korakov, ki so odvisni od The first patent refering to a MWT device was registered in Belgium in 1945. Practical experience with these devices showed very different results: from very effective to completely useless [2]. Since 1960, strong electromagnets have been used in the Soviet Union for scale control in high-temperature water systems with significant economic benefits [3]. In the USA, MWT devices have been accepted since 1975 ([4] and [5]). 1 THE EFFECTS OF MWT DEVICES ON NATURAL AND INDUSTRIAL WATERS The practical use of MWT devices has become increasingly wide spread for descaling or scale prevention and has penetrated into new fields for other purposes such as biochemistry, medicine, agriculture, dispersion separations, concrete and fuel amelioration ([6] to [12]). In all these cases fluids containing some fraction of water were magnetically treated to improve their biochemical or physicochemical properties. The scale-forming components ( mainly CaCO3 in low-temperature systems and CaSO4 in heated systems ) precipitate from zhe magnetically treated water in a suspended form rather than by forming hard-scale linings. The crystals are different in terms of their form, size and structure with lowered adhesivity. For CaCO3 it was observed that the ratio of aragonite/calcite crystal phases could be increased ([13] and [14]). The former is a kinetically advanced crystal phase of CaCO3 formed in needle–like crystals which have low adhesion, while the latter is a thermodynamically advanced crystal phase of CaCO3 formed in rhombic crystals which are able to adhere into compact, hard-to-remove scale. The increased aragonite/calcite ratio partially explains the precipitation of powder deposits resulting from MWT. Although the crystallization in magnetically treated water is strongly dependent on the water composition and working conditions the precipitation of fever and larger CaCO3 crystals with an increased fraction of aragonite was observed in most cases. Even the crystallization in a supersaturated mixture of static magnetically treated solutions of Na2CO3 and CaCl2 under well-controlled laboratory conditions gave similar results [15]. 2 MECHANISMS OF MWT – ACTING ON PROCESSING WATER A long history of practical experiences has provided some empirical bases for designing magnetic devices. However, the mechanism which explains how the magnetic field acts on the treated water still remains uncertain. From the many reports relating to laboratory and theoretical research it can be concluded that the mechanism most probably consists of parallel interacting steps, depending on the construction of the MWT devices, the composition of the supplied water as a | gfin=i(gurMini5nLn 00-8_____ stran 533 I^BSSIfTMlGC A. Pristovnik - L.^. Lipu{ - J. Krope: Spremenjeno kristaljenje - Modified Scale Crystallization delovnih razmer (npr. hitrosti pretakanja vode in temperature). V svetovni literaturi je najti dragocene namige, ki poskušajo pojasniti magnetne učinke, vendar nobeden ni dokončno potrjen in tudi ne pojasni vseh učinkov hkrati. Vodilne hipoteze so: - magnetno spremenjena hidratacija ionov in trdnih površin - magnetohidrodinamični učinek na vodne disperzije - koncentracijski učinki v delovnih kanalih naprav MOV. Slednji se štejejo kot zvišanje verjetnosti trkov med ioni ali trdnimi delci v določenih območjih delovnih kanalov zaradi turbulence pretakajoče se vode, visoke magnetnosti suspendiranih korozijskih produktov oz. nehomogenosti magnetnega polja naprave [16]. Učinki tega tipa delno pojasnijo agregacijo drobnih že destabiliziranih delcev v večje, medtem ko je spremenjeno kristaljenje in destabilizacijo dispergiranih komponent, ki tvorijo vodni kamen, laže pojasniti s prvima dvema hipotezama. Kateri mehanizem bo prevladal, je odvisno od sestave vode in samih razmer pri obdelavi. V nadaljevanju bo govor o mogočih vzrokih spremenjenega kristaljenja CaCO3. 2.1 Učinek magnetno spremenjene hidratacije na kristaljenje CaCO3 Eksperimentalna opazovanja vodnih raztopin so med statičnim izpostavljanjem magnetnemu polju pokazala spremembe v nekaterih fizikalno-kemijskih lastnostih, npr.: svetlobni absorbanci [17], viskoznosti [18], topilni entalpiji [19], električni prevodnosti [6], površinski napetosti [20], dielektričnosti [21] in tudi v kristaljenju ter stabilnosti koloidov ([22], [15] in [23]). Opažanja podpirajo hipotezo o magnetno spremenjeni hidrataciji. 1. Posledica tega je, da z nižjo energijo lahko pozitivno vplivamo na obratovalne stroške takega hladilnega sistema. Slika 2 kaže ta dejstva za različne razmere delovanja (podatki za hladilni sistem Briickenski ulici). 2 HLADILNI OBRAT BRUCKEN V MESTU GERA Da bi bolje uporabili sedanjo parno mrežo in nov obrat za proizvodnjo električne energije in toplote (KPET), je bil Fraunhofski UMSICHT določen, naj razišče prednosti kombinirane dobave toplotne energije in hladu. Od leta 1996 je v obratovanju nov postroj KPET (P l = 76 MW, Q = 140 MW). Omrežje summer with high air humidity and high outside tempera-tures, the coefficient of performance of an SJEC is lower than the COP of ACCs. Over the period of a year the re-cooling water temperatures, however, lie well below these conditions of the design case so that an average COP > 1 can be reached. As a consequence, the lower demand of driving energy positively effects the running costs of the chiller plant. Figure 2 shows these facts for different operating conditions (data for the BriickenstraBe chiller plant). 2 THE CHILLER PLANT BRUCKENSTRASSE IN CITY OF GERA In order to use the existing steam network and the new CHP plant (gas turbine combined cycle) of EGG in an improved way, Fraunhofer UMSICHT was engaged to investigate the benefits of a combined district heating and cooling supply. Since 1996 the new CHP plant (P l = 76 MWl, Qth = 140 MWth) stran 551 glTMDDC 5 P. Noeres, D. Hölder, W. Althaus: Kombinirano daljinsko ogrevanje - A Combined District Heating daljinskega sistema povezuje 244 MW in ga sestavlja parni del (primarni del) in vročevodni del (sekundarni del). Obe omrežji sta povezani z 12 postajami. Glede na sedanje stanje (parni sistem v središču mesta) je tehnologija parnega ejektorskega hlajenja zelo obetajoča. Uvodne raziskave so obsegale izračun potrebe po hladu in ocenitev posledic daljinskega ogrevanja in hlajenja na proizvodnjo električne energije in toplote (KPET). Z uporabo teh podatkov je bila izračunana potreba po hladu v mestu Gera. Na podlagi teh podatkov so na Fraunhofer UMSICHT začeli z načrtovanjem hladilnega sistema s hladilno močjo 1,2 MW. Na podlagi rezultatov je Fraunhofski UMSICHT prišel do sklepov, da je uporaba parnega hladilnega sistema tehnično mogoča, stroškovno učinkovitejša v primerjavi z drugimi hladilnimi sistemi in tudi gospodarnejša. Celotna hladilna zmogljivost hladilnega sistema se doseže s parnim ejektorjem in kompresijskim hladilnikom, vsakim s po 600 kW. Ta delitev na eni strani zagotavlja optimalno delovanje in na drugi visoko zanesljivost delovanja. Ejektorski hladilni sistem (PES) sestoji iz dveh delov, od katerih vsak vsebuje tri parne ejektorje. Za zmanjšanje količine gonilne pare je vstavljen parni ventil, ki krmili tlak pare in kot posledico porabo pare glede na tlak v kondenzatorju. Preglednica 1 podaja povzetek podatkov sistema PES: has been in operation. The district heating network has a connected load of 244 MW and consists of a steam net (primary net) and a hot-water net (secondary net). Both nets are connected by 12 transfer stations. Due to the favorable prerequisites (a steam net up to the downtown area) the use of steam-jet ejector chiller technology was very promising. The preliminaries for the development of a strategy included a cold demand survey and an estimation of the consequences of a combined district heating and cooling supply for the operation of the CHP plant. With this data the cold demand in downtown Gera was determined. On the basis of this data Fraunhofer UMSICHT was entrusted with the planning of the first chiller plant with an installed chiller capacity of 1.2 MWth. As a result of the basic engineering Fraunhofer UMSICHT came to the conclusion that the use of a steam jet refrigerating system is technically possible and cost-effective compared to other chiller systems. The total chiller capacity of the chiller plant is covered by a steam-jet ejector chiller unit and a compression chiller with 600 kWth each. This partitioning ensures optimal operating conditions for the SJEC and a high supply guarantee for the chiller. The SJEC consists of two stages, each of them with three steam-jet ejectors. To reduce motive-steam demand a motive-steam control valve is used to control the motive-steam pressure and, as a consequence, the steam consumption, depending on the condenser back-pressure. Table 1 gives a summary of the design data of the SJEC: Preglednica 1. Imenski podatki delovanja Parne ejektorske hladilne enote v mestu Gera Table 1. Nominal Operation Data of the Steam-Jet Ejector Chiller Unit in City of Gera hladilna moč PES chiller capacity SJEC 600 kWth temperatura hladne vode chilled water temperature 6 / 12 °C temperatura hladilne vode (dotok odtok) re-cooling water temperatures (supply line / return line) 25 / 30 °C temperatura okolice wet bulb temperature (design) 21 °C parametri gonilne pare motive steam parameter (district heat) 143 "C, 3 bar HŠ (imensko, povprečje) COP (nominal, assumed average) 0,55 / 1 Hladilni postroj je shematično prikazan na sliki 4. Dva hladilnika sta povezana vzporedno na strani hladne vode. Hidravlično sta povezana s hladnovodnim omrežjem in s hranilnikom hladne vode, tako da je prostorninski tok skozi uparjalnik kompresorskega cikla (KC - CC) in skozi uparjalnik parnega ejektorskega cikla (PES) nadzorovan neodvisno od prostorninskega toka do hladilnega obrata. Kondenzatorja PES in KC sta vezana zaporedno na hladno vodo, tako da dosežemo najmanjši pretok hladne vode. Parni ejektorski hladilni The chiller plant is shown schematically in Figure 4. The two chillers are connected in parallel on the cold-water side. They are decoupled hydraulically from the chilled water net by a cold water storage so that the volume flows through the evaporator of the CC and the flash evaporator of the SJEC can be controlled independently of the net volume flow to the chiller plant. The condensers of the SJEC and the CC are switched in series on the re-cooling water side to obtain a re-cooling water volume flow as low as possi- VH^tTPsDDIK stran 552 P. Noeres, D. Hölder, W. Althaus: Kombinirano daljinsko ogrevanje - A Combined District Heating proces (PES) je neposredno povezan z omrežjem EGG daljinskega hladilnega sistema in omrežjem parnega sistema. Hladilni krog, ki vsebuje hladilne stolpe, je bil hidravlično povezan s kondenzatorjem s ploščnimi prenosniki toplote. ble. The SJEC is linked directly to EGG’s district cooling system and district heating steam network. The re-cooling cycle containing the cooling towers was decoupled hydraulically from the condenser water cycle of the SJEC by a plate heat exchanger. para (daljinsko ogrevanje) steam (district heat) 0,2- 3 bar (op) Kx^ G h,i,2,°C. »„*. omrežje chilled water net 6 °C >!< CM) kompresorski hladilnik compressor chiller (CC) 3 86 m /h X parni ejektor / steam jet ejector propustni vent l overflow valv -----HX X hranilnik 3 172 m /h hladne vode cold water storage 86 m 3 /h O A pršilni kondenzator spray condenser 20 - 50 mbar (abs) XL uparjalnik flash evaporator 11,4 mbar/9 mbar (abs) ploščati prenosnik toplote plate heat exchanger hladilni stolp cooling tower 32 °C dodatna _, voda X additional water 290 m 3 /h X 25 °C hranilnik hladne vode recooling water storage izstop vode water release Sl. 4. Shema procesov hladilnega obrata Fig. 4. Process-Flow Scheme of the Chiller Plant 3 EKONOMSKA OCENA Za ekonomsko oceno toplotno gnanih hladilnih procesov je treba upoštevati tako investicijske kakor tudi obratovalne stroške. Specifični investicijski stroški parnega ejektorskega hladilnega procesa (PES), vključno z dodatki za pilotni obrat v Geri so - za hladilni obrat v Briickenski ulici - malo višji kot stroški za absorpcijski hladilni sistem pri istih pogojih delovanja. V tej točki je treba upoštevati, da so za pilotni objekt stroški za proizvodnjo in načrtovanje razmeroma visoki. Poleg tega je bilo potrebno na pilotnem objektu izvesti številne meritve in nadzora. Izbran PES je samo en izveden hladilni obrat. V nadaljevanju je pričakovati nižje investicijske stroške v primerjavi z absorpcijskih sistemom (AHS) za enake robne pogoje, ki jih lahko dosežemo z masovno proizvodnjo in nadaljnjim optimiranjem hladilnega sistema. Za ekonomsko oceno je treba upoštevati tudi obratovalne stroške. V tem primeru je prednost PESa zaradi večjega letnega deleža delovanja (HŠ). Specifično vrednost lahko izračunamo iz podatkov hladilne obremenitve in stanja zraka (vlažnosti in temperature). Za primer Gera naj bi letni delež delovanja dosegel vrednost približno 1. Kot 3 ECONOMIC EVALUATION For an economical evaluation of thermally driven refrigerating processes both the investment costs and the running costs have to be considered. The specific investment costs of the SJEC including auxiliaries for the pilot plant in Gera are, for the chiller plant BriickenstraBe, a little higher than the costs of an absorption chiller under the same operating conditions. At this point it has to be taken into account that for a pilot plant the expenditures for production (single manufacturing) and planning were still relatively high. Additionally, a lot of measuring and control techniques were equipped in the pilot plant. Furthermore, the chosen SJEC is a single manufactured chiller. In the future, lower investment costs compared to an ACC have to be expected for equal boundary conditions, which could be made possible by series production and further optimization in chiller-plant design). For the economic evaluation of cold generation the running costs have to be taken into account as well. Here, advantages for the SJEC technology arise due to the larger annual mean COP. This specific value can be calculated from data on cooling-load duration curves and the state of the ambient air (humidity and temperature). For the supply case in Gera the annual mean COP was supposed to achieve a value of P. Noeres, D. Hölder, W. Althaus: Kombinirano daljinsko ogrevanje - A Combined District Heating rezultat pilotnega objekta in obratovalnih izkušenj je HŠ od 0,9 do 1 in je ugodna ocena za nadaljnje uporabe (število HŠ je za absorpcijske klimatske naprave (AHS) pogosto slabši od 0,6). Za izračun obratovalnih stroškov toplotnih hladilnih procesov uporabljajo naslednje predpostavke, ki so tipične za pridobivanje hladu v Nemčiji. approximately 1. As a result of the pilot plant and the operational experiences an annual mean COP of 0.9 to 1 is a suitable estimation for further application (in reality the COP number of ACCs is often worse than 0.6). To calculate the running costs of thermally driven refrigeration processes the following assumptions are chosen, as these are typical for a cold supply in Germany. Preglednica 2: Podatki za izračun obratovalnih stroškov (samo kot primer) Table 2. Preliminaries to calculate operating costs (only as an example) količnik f (razmerje med vodovodno in odpadno vodo) 3 factor f (ratio of tap water to waste water)_____________________________________ poraba elektrike na kW hladilne moči electricity demand per kW re-cooling demand______________________________________ voda (vključno s pripravo, kemični stroški) 1,02 Euro/m2 water (including make-up, chemical costs)_________________________________________ odpadna voda 1,53 Euro/m3 waste water__________________________________________________________________ 0,025 kWel/kWth energija, elektrika energy rate, electricity 0,071 Euro/kWh cena elektrike demand price tariff, electricity 102 Euro/kW/a ure dobave hladu pri polni obremenitvi full load hours cold supply 1000 h/a obratovalne ure dobave hladu operating hours cold supply 5000 h/a specifični stroški toplote specific costs of heat 20,47 Euro/MWh Euro/MWh 100,00 90,00 80,00 70,00 60,00 50,00 40,00 30,00 20,00 10,00 0,00 0 0,5 Hč 1 Ho / COP 1,5 Sl. 5. Specifični stroški obratovanja toplotno gnanih hladilnikov Fig. 5. Specific operation costs of thermally driven chillers Ugotovimo močno odvisnost obratovalnih stroškov od HŠ. S parametri za EU-AHS (HŠ = 0,6) lahko napovemo specifične obratovalne stroške približno 60 Euro/MW . Specifični stroški obratovanja za PES z letnim HS 0,9 (imensko delovanje 0,55) so okoli 25% nižji. Če povzamemo, lahko ugotovimo nižje stroške (obratovalne in investicijske) za dane karakteristike porabnikov. We see the strong dependence of running costs from the COP. With the parameters for an SE-ACC (COP=0.6) given here we have to assume specific operating costs of approximately 60 Euro/MWhth . The specific operating costs of an SJEC with an annual mean COP of 0.9 (nominal operating case 0.55), however, are around 25% lower. In summary, a lower total cold-supply cost (operating and capital costs included) can be realized for the given supply characteristics of the customers. VH^tTPsDDIK stran 554 P. Noeres, D. Hölder, W. Althaus: Kombinirano daljinsko ogrevanje - A Combined District Heating 4 IZKUŠNJE DELOVANJA Hladilni obrat deluje dve leti. V tem času ni prišlo do nobene nezgode ali motnje pri dobavi hladne vode. Poraba hladne vode je bila pričakovana gledano predvsem letno (sl. 6). Karakteristike delovanja parnega ejektorja so bile zelo dobre, predvsem kakovost nadzora hladne vode. Zadnje leto je bilo HŠ 0,62, kar je malo slabše od pričakovanega 1. Razlog za manjše HŠ je nižja temperatura povratne hladne vode, vmesno odpravljanje ovir krmiljenja gonilnega parnega toka in ne optimalna konstrukcija ejektorjev Z instaliranim sistemom krmiljenja gonilne pare ni bilo mogoče znižati tlaka pare pod 0,2 bar (sl. 7). Zaradi tega do tedaj ni bilo mogoče uporabiti odličnih pogojev delovanja parnega ejektorja v zimskem času in ob spremembah. Za to leto pričakujemo boljše obratovalne rezultate zaradi boljše (oz. višje) temperature hladne vode, ker so 4 OPERATIONAL EXPERIENCES The chiller plant has been in operation for two years. During this period no accidents or interruptions of the chilled-water supply occured. The chilled-water demand corresponds to the expectations, especially concerning the year-round base demand for chilled water (Fig. 6). The operational characteristics of the steam-jet ejector are very good, especially the quality of the chilled-water supply control. For the last year the mean COP was 0.62, which is a little worse than the expected value of about 1. The reason for the reduced COP was the lower chilled-water return temperatures, in the meantime cleared constraints of motive steam flow control and a non-optimal design of ejectors are suspected. With the installed motive-steam control systems it was not possible to lower the motive-steam pressure below 0.2 bar(op) (Fig. 7). Because of this it was not possible, until now, to use the excellent operation conditions of a steam-jet ejector in winter time and transfer period in a complete matter. For this year we expect better performance data due to a better (or higher) chilled-water return-line temperature, a new 1,20 1,10 1,00 0,90 temperatura kondenzatorske vode temperature condenser water 0,70 - 0,60 0,50 0,80 ^^Wg^AvsMA^ temperatura mokrega termometra---------- wet-bulb temperature Afy^^^N^W 30 25 20 15 10 5 0 00:00 04:00 08:00 20:00 00:00 05.11.1999 ^ 09.09.1999 12:00 16:00 čas / time Sl. 6. Hladilni obrat v Briickenski ulici - HŠ in različne obratovalne temperature (podatki 19.5.1999) Fig. 6. Chiller Plant Briickenstrafie - COP and different operation temperatures (data 19.05.1999) 2 1,8 1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 \ *11 H L x - x , x -0,50 0,50 1,50 2,50 bar (op) ,50 tlak gonilne pare motive-steam pressure Sl. 7. Hladilnik v Briickenski ulici - HŠ v odvisnosti od tlaka pare (podatki 19.5.1999 in 09.09.1999) Fig. 7. Chiller Briickenstrafie - COP as function of motive steam pressure (data 05.11.1999 and 09.09.1999) stran 555 glTMDDC P. Noeres, D. Hölder, W. Althaus: Kombinirano daljinsko ogrevanje - A Combined District Heating bili januarja letos vgrajeni nov krmilni sistem gonilne motive-steam contol system and modified motive-steam noz- pare in parne šobe. zles, which were changed in January of this year. 5 SKLEP Izkušnje delovanja obrata iz prvih dveh let so zelo ugodne. Med prvo fazo delovanja in prvo fazo optimiranja so bili začetni problemi zelo hitro rešeni. Neučinkovito delovanje, ki je zelo znano pri večini toplotno gnanih hladilnih procesih, ni bilo ugotovljeno pri parnem hladilnem procesu. Dinamično obnašanje PES je primerljivo z drugimi običajnimi kompresorskimi hladilniki. V tem trenutku poteka optimizacija delovanja hladilnika predvsem HŠ in krmilnega sistema izklopa. 5 CONCLUSION The experience from the first two years of the plant’s operation are very positive. During the primary phase of operation and the first optimization phase the initial operational problems of the pilot plant could be solved very quickly. The inert operating response, well known from many heat-driven refrigerating processes was not observed for the steam-jet refrigeration system. In their dynamic behaviour SJECs are comparable to conventional compression chillers. At the moment the optimization of chiller operation, especially COP and switch-off control systems is in progress. 6 SIMBOLI 6 SYMBOLS absolutno abs absolute absorpcijski hladilni krog AHS - ACC absorption chiller cycle kompresorski hladilni krog KHK - CCC compression chiller cycle kombinirano daljinsko ogrevanje in daljinsko KDODH - combined district heating and district hlajenje - CDHDC cooling kombinirana proizvodnja toplote, hladu in KPTHM - combined heating, cold, and power elektrike - CHCP kombinirana proizvodnja toplote in elektrike KPET - CHP combined heat and power hladilno število HŠ - COP coefficient of performance daljinsko ogrevanje DO - DH district heating razmerje dodatne vode f ratio additional water to released water nadtlak op over-pressure enojni učinek EU - SE single effect parni ejektorski hladilnik PES - SJEC steam jet ejector chiller temperatura T (°C) temperature 7 LITERATURA 7 REFERENCES [1] Noeres, P., Holder, D., Althaus, W., B. Petzold (1999) Economic cold generation by steam jet refrigeration -experiences from a pilot plant. 7th International Symposium on District Heating and Cooling, Lund, Sweden, May 18-20. [2] Holder, D., P. Noeres, W. Althaus, B. Petzold (1999) Fernkalteversorgung mit Dampfstrahlkaltetechnik bei der Energieversorgung Gera. EUROHEAT & POWER - Fernwarme international 9/1998, 34-42. Naslov avtorjev: Peter Noeres Daniel Holder dr. Wilhelm Althaus Inštitut za okolje in varno tehnologijo Osterfelder Str. 3 D-46047 Oberhausen, Nemčija Authors’ Address: Peter Noeres Daniel Holder Dr. Wilhelm Althaus Fraunhofer - Institute for Environment and Safety Technology Osterfelder Str. 3 D-46047 Oberhausen, Germany Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 VH^tTPsDDIK stran 556 © Strojni{ki vestnik 46(2000)8,557-563 ISSN 0039-2480 UDK 697.97:621.574.013 Pregledni znanstveni ~lanek (1.02) © Journal of Mechanical Engineering 46(2000)8,557-563 ISSN 0039-2480 UDC 697.97:621.574.013 Review scientific paper (1.02) Energetska u~inkovitost daljinskega hlajenja za klimatizacijo prostorov The Energy Efficiency of District Cooling for Space Conditioning Alojz Poredo{ Oskrba uporabnikov z grelno in hladilno energijo iz daljinskih energetskih sistemov bistveno prispeva k smotrni porabi energije in varovanju okolja. V preteklih nekaj letih se je uporaba daljinskega hlajenja v nekaterih državah pomembno zvečala. Uporaba absorpcijskih hladilnikov za daljinsko hlajenje se v zadnjem desetletju prav tako povečuje. Te hladilne naprave potrebujejo vir toplote za svoje delovanje. To je lahko plin, kurilno olje, para ali vroča voda. V članku so podani rezultati raziskave vplivnih parametrov na specifične izgube toplote v vročevodnem omrežju in celotni učinek daljinskega hladilnega sistema. © 2000 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: hlajenje daljinsko, naprave hladilne, učinkovitost energijska, izgube toplotne) Supplying customers with heating and cooling energy from district energy systems contributes to the rational use of energy and to environmental protection. In the past few years, the use of district cooling has significantly increased in some countries. In the last decade, the use of absorption chillers for district cooling has increased. These chillers need a heat source for their operation. It can be gas, fuel oil, steam or hot water. This paper presents the results of research on the parameters which influence the specific heat losses in a district heating network and the overall efficiency of the system. © 2000 Journal of Mechanical Engineering. All rights reserved. (Keywords: district cooling, absorption chillers, energy efficiency, heat losses) 0 UVOD Dvig ravni delovnih in bivalnih pogojev ljudi je nujno povezan s hlajenjem v okviru klimatizacije. V te namene se uporablja različna naključno izbrana oprema različnih proizvajalcev brez ustreznega zagotavljanja učinkovitosti ter tehnične in okoljne neoporečnosti. Posledica tega je povečana poraba elektrike kot najbolj kvalitetne energije. Rešitev tovrstnih problemov se ponuja z daljinskimi hladilnimi sistemi. Rezultati številnih študij v svetu kažejo, da imajo v primerjavi z lokalnim hlajenjem z uporabo električne energije daljinski hladilni sistem številne prednosti. Daljinski hladilni sistemi so dokazano okolju bolj prijazni kot posamezne manjše hladilne enote. Z njimi zmanjšujemo oddajo škodljivih snovi, z uporabo sorpcijske tehnike hlajenja pa lahko povsem izločimo ozonu škodljiva hladiva. Kadar so hladilne naprave gnane s toploto iz kogeneracije, neposredno zmanjšu- 0 INTRODUCTION An increase in the quality of working and living conditions is inevitably connected with cooling as part of air-conditioning systems. Various types of equipment produced by different manufacturers are used for this purpose, they are selected at random and do not provide any assurance as to efficiency and compliance with technical and environmental standards. This has resulted in an increase in the consumption of electrical energy: the energy of the highest quality. A solution tor such problems is offered by district cooling systems. The results of numerous studies in the world have shown that in comparison with local cooling using electrical energy, district cooling systems have numerous advantages. District cooling systems have been proven to be more environmentally friendly than individual smaller cooling units. They reduce the emissions of hazardous substances and, with the use of a sorption cooling technique, ozone-unfriendly refrigerants can be eliminated gfin^OtJJlMISCSD 00-8 stran 557 |^BSSITIMIGC A. Poredo{: Energijski u~inek daljinskega hlajenja - The Energy Efficiency of District Cooling jemo toplotno obremenitev okolja, z uporabo plina za njihov pogon pa odpadejo vmesne pretvorbe energije in dodatne izgube [1]. Odločitev za uporabo absorpcijskih ali kompresorskih hladilnih naprav je odvisna predvsem od investicijskih in obratovalnih stroškov. Investicijski stroški so nekoliko večji za absorpcijske hladilne naprave in so odvisni od tipa hladilnika ter od vrste toplotnega vira. Eden od odločilnih kriterijev izbire vrste hladilnika je lahko tudi ekološka primernost. Absorpcijske hladilne naprave delujejo skoraj neslišno. Uporabljajo tudi hladiva, kot npr. amoniak, litijev bromid in vodo (NH3 - HO, LiBr -HO), ki imajo vpliv na nastanek tople grede (GWP) in vpliv na tanj sanjeozonske plasti (ODP) enak nič. Če upoštevamo porabo primarne energije (določeno z ekvivalentom električne energije, ki je potrebna za pogon kompresorskih hladilnih naprav), imajo nekatere absorpcijske hladilne naprave manjšo porabo, kakor prikazuje sl. 1. Z vročo vodo in s paro gnani absorpcijski hladilniki lahko uporabljajo toploto odvzeto iz kogeneracijskega sistema. Zaradi odvzema toplote iz parne turbine v kogeneracijskem sistemu se zmanjša pridobljena električna energija. V primeru plinsko gnanih absorpcijskih hladilnih naprav je upoštevana učinkovitost plinsko gnanih turbin, ki je potrebna za določitev ustrezne električne moči. Če primerjavo različne vrste hladilnih naprav, vidimo, da predstavljajo z vročo vodo in s paro gnani dvostopenjski absorpcijski hladilniki najmanjšo porabo ekvivalenta električne energije na enoto hladu, kar je lahko tudi eden izmed načinov zmanjšanja emisij CO2. completely. When cooling devices are driven by heat from cogeneration, the thermal burden on the environment is reduced directly, while using gas to drive them means the intermediary stages of energy conversion and additional energy losses are avoided as well [1]. The decision, whether to use absorption chillers or compressor chillers basically depends on the investment and operational costs. The investment costs for absorption chillers can be a little higher, depending on the type of the absorption chiller and the heat source in use. One of the criteria for the decision could be also the ecological aspect. Absorption chillers are almost noiseless during operation. They also use the refrigerants, such as amonia (NH3 - H2O) and water (LiBr - H2O), which have a global warming potential (GWP) and ozone depleting potential (ODP) equal to zero. When the primary energy consumption is considered (defined by the equivalent electrical power which is needed for driving the compressor chillers, and which could be produced by the heat source for absorption chillers), some of the absorption chillers have a reduced consumption as shown in Figure 1. Hot-water and steam-driven absorption chillers use heat extracted from a cogeneration plant. Because of the heat extracted from a steam turbine in a cogeneration plant, less electrical power will be produced. In the case of a gas-driven absorption chiller, the efficiency of a gas-driven turbine is considered necessary to determine the equivalent electric power. Comparing different types of chillers, hot-water and two-stage steam-absorption chillers present the lowest equivalent electric power per unit of cold pro- % 140 120 100 80 60 40 20 0 kompresor vroča voda para (ena stopnja) para (dve stopnji) compressor hot water steam (one stage) steam (two stage) tip hladilne naprave type of the chiller plin gas Sl. 1. Delna hladilna obremenitev hladilnika na enoto ekvivalenta električne moči [2] Fig.1. Cooling capacity share per unit of equivalent electrical power [2] VH^tTPsDDIK stran 558 A. Poredo{: Energijski u~inek daljinskega hlajenja - The Energy Efficiency of District Cooling Plinsko gnane absorpcijske hladilne naprave predstavljajo največjo porabo ekvivalenta električne energije na enoto hladu. V primerjavi z drugimi hladilnimi napravami so tudi investicijski stroški največji. Če upoštevamo, da lahko plinsko gnana absorpcijska hladilna naprava nadomesti tudi vročevodni kotel v nekem objektu, je njihova uporaba upravičena. 1 SPECIFIČNE TOPLOTNE IZGUBE Najboljša izvedba sistemov daljinskega hlajenja je v kombinaciji z absorpcijskimi hladilniki, povezanimi v sistem daljinskega ogrevanja. Ti sistemi morajo delovati tudi v poletnem obdobju zaradi zagotovitve toplote, potrebne za ogrevanje tople sanitarne vode. To pa predstavlja razmeroma velike relativne izgube glede na količino dobavljene toplote. Z vročo vodo gnani absorpcijski hladilniki potrebujejo za svoje normalno delovanje višje temperature, kot so običajno pri obratovanju sistema daljinskega ogrevanja v poletnem obdobju S povišanjem temperature dovoda in povratka vroče vode se povečujejo toplotne izgube omrežja, s tem pa tudi specifične toplotne izgube (kW. JMWdob l ). S povečanjem odjema za potrebe hlajen gub a se lahko specifične toplotne izgube zmanjšajo (sl. 2). Temperaturna razlika med dovodom in povratkom vroče vode v omrežju daljinskega ogrevanja nima vpliva samo na toplotne izgube, ampak tudi na porabo električne energije, ki je potrebna za pogon obtočnih črpalk. Za dosego večje učinkovitosti z vročo vodo gnanih absorpcijskegih hladilnikov mora biti temperaturna razlika med dovodom in povratkom čim manjša. Povečanje temperature dovoda vroče vode 700 kW/MW 650 600 550 500 450 {. 400 - 350 300 250 200 150- 100 -50 0 duced. This could also be a way of introducing state support in a sense of reduced CO2 emissions. Gas absorption chillers have the biggest equivalent electrical power consumption. Their investment costs are also higher when compared to the other chillers. As they can also replace the boiler for heat production, there is no doubt about their advantages over compressor chillers. 1 SPECIFIC HEAT LOSSES District cooling systems with sorption chillers are the best when dsigned in combination with district heating systems, the majority of which also have to operate in the summer in order to ensure the supply of sanitary water. But this means a large relative loss with regard to the amount of supplied heat. Absorption chillers, driven with hot water, need heat with higher temperatures for their normal operation as the district heating network. By increasing the supply and return temperatures of hot water, the heat losses of the district heating network are higher and so also are the specific heat losses (kWlosses/ MWheat supply). But with increasing heat consumption, the specific heat losses decrease (Fig. 2). The supply- and return-temperature difference for a district heating network does not have an influence only on heat losses, but also on the consumption of electrical energy needed to drive network pumps. To achieve high chiller efficiencies, the supply and return hot-water temperature difference should be low. Increased hot-water supply tempera- Tinp (°C) ^-85 -¦-90 0 15 30 45 60 75 90 105 120 povečanje porabe toplote MW increased heat consumption Sl. 2. Specifične toplotne izgube vročevodnega omrežja[3] Fig. 2. Specific heat losses of a district heating network [3] gfin^OtJJlMISCSD 00-8 stran 559 |^BSSIfTMlGC A. Poredo{: Energijski u~inek daljinskega hlajenja - The Energy Efficiency of District Cooling in zmanjšanje temperaturne razlike pa poveča toplotne izgube v omrežju daljinskega ogrevanja. 2 UČINKOVITOST ABSORPCIJSKE HLADILNE NAPRAVE Analiza posameznih učinkovitosti je temeljila na obratovalnih parametrih vročevodnega absorpcijskega hladilnika Carrier (16 JB 032 /036) z enojnim efektom in delovno snovjo Li-Br. Parametri obratovanja so bili: a) temperatura hlajene vode (6/12°C) b) temperatura hladilne vode (27/32°C) Rezultati kažejo, da se hladilno število hladilnika povečuje z višanjem temperature dovoda vroče vode in z manjšanjem temperaturne razlike med dovodom in povratkom. Iz slike 3 je razvidno, da je razlika med največjo in najmanjšo vrednostjo hladilnega števila samo okrog 5%. Temperatura dovedene vroče vode je omejena z najnižjo temperaturo. Pri nižji temperaturi dovoda (< 85 °C ), je učinkovitost absorpcijskih hladilnikov zelo majhna in so zato specifični investicijski stroški previsoki. Pri teh pogojih se pojavijo tudi problemi v samem delovanju absorpcijskega hladilnika. Bistvo naše analize je bila določitev temperaturnega območja obratovanja omrežja daljinskega ogrevanja, v katerem dosežemo ustrezno učinkovitost tako absorpcijskega hladilnika kot tudi celotnega omrežja daljinskega ogrevanja. 0,735 0,73 0,725 0,72 0,715 0,71 0,705 0,7 0,695 0,69 rtn]nrmn nhmnrir i determined area ^ ^^*—~x ! ^r ! i j*/ i ^ix------' / /s....- « 75% uporabljena odpadna toplota recoverable waste heat > 2 kWh @2 kW izhod / output > 11 kWh @7 kW izhod / output gorivo fuel naravni plin utekočinjen propan natural gas liquid propane intervali servisiranja maintenance intervals 9000 h projektna doba trajanja design life 15 let 15 years 4 TRDNO OKSIDNA GORILNA CELICA V KOMBINACIJI S PLINSKO TURBINO Plinske turbine v kombinaciji s trdno oksidno gorilno celico (TOGC - PT) so bile obravnavane v številnih študijah ([6] do [9]), toda številne so obravnavale MW postrojenja. Dandanes so na voljo številne nove možnosti, ker je interes za proizvodnjo elektrike v mikro turbinah (30 do 200 kW). Številna podjetja, ki se ukvarjajo z mikro turbinskimi generatorji, sedaj oglašajo svoje izdelke za končne uporabnike, družbe in proizvajalce energije ([10] in [1]). To pospešuje uporabo TOGC s PT celo v stanovanjskih objektih, kjer 200 kWe plinska turbina daje izhodno moč 30kWe. 4 SOLID OXIDE FUEL CELLS IN COMBINATION WITH A GAS TURBINE Studies of a gas-turbine cycle with a solid-oxide fuel cell (SOFC-GT) have been carried out by several researchers ([6] to [9]), but most of them have been considering MW sized power plants. Recently, new opportunities have arisen as there has been a sustained interest in power applications for microturbines (30 to 200 kW), and several microturbine-generator manufacturers are now announcing commercial availability of their products, targetting end-users, utilities and energy service providers ([10] and [1]). This context facilitates the SOFC-GT integration even for residential co-generation, where, for example, the gas-turbine output of a 200 kWe system is calculated to be approximatively 30 kWe. 00-8 VBgfifWEBS stran 584 R. Taccani: Kogeneracija z gorilnimi celicami - Co-Generation Using Fuel Cells V TOGC visoke temperature (~1000°C) zagotavljajo, da vse sestavine goriva, v kombinaciji s potrebno količino vodne pare, oksidirajo v trenutku in dosežejo termodinamično ravnotežje, če dovedemo zadostno količino zraka. Zaradi visokih temperatur so drage reakcije nepotrebne kar omogoča neposredno porabo goriva v sami celici. Ker je trdni elektrolit normalno zelo stabilen, ni premikanja elektrolita. Raziskujejo dva različna modela: cevni model in ravninski model. V našem delu smo uporabili cevni model. Shematična predstavitev krožnega procesa je prikazana na sliki 3. Prej obdelano gorivo (metan) in oksidant (zrak) vstopata v gorilno celico po kompresiji. Oksidacija poteka večinoma v gorilni celici. Celotna reakcija pa se konča v zgorevalni komori. Zgoreli plini pod tlakom odtekajo skozi turbino. Izstopna para iz turbine zagotavlja toploto ne samo za pripravo goriva, ampak tudi za pridobivanje tople vode. In SOFCs the high temperatures (~1000 °C) ensure that all fuel compositions, when combined with the necessary amount of water vapor, will oxidize rapidly and reach thermodynamic equilibrium if sufficient air is provided. The high temperature makes expensive reactions unnecessary and permits direct processing of fuel in the fuel cell itself (i.e. internal reforming). Because the solide-oxide electrolyte is normally very stable, no electrolyte migration problems exist. Basically two different designs are under development: the tubular design and the planar design. In our work we have been considering the tubular design. A schematic view of the considered cycle is presented in Figure 3. The preprocessed fuel (methane) and the oxidant (air) enter the fuel cell after being compressed. The fuel oxidation reaction occurs predominantly within the fuel cell. The reaction is completed in a combustion chamber. The pressurized-fuel combustion products are exhausted through a turbine. voda water "0" izpuh exhaust /prenosnik toplote heat exchanger rekuperacija toplote heat recovery kompresor compressor prenosnik toplote heat ^J-^ exchanger ^/ /V\ gorivo fuel V > Y TOGC SOFC zrak air turbina expander generator Sl. 3. Obtočni diagram krožnega procesa s TOGC Fig. 3. SOFC-GT cycle flowsheet diagram Za raziskavo procesa smo uporabili simulirni računalniški program, ki je vseboval tudi simuliranje trdno oksidne gorilne celice, napisane v jeziku Fortran ([11] in [12]). Simulirni model je bil razvit za raziskovanje: - delovne temperature in tlaka, - sestav plinov reaktantov, - izkoristka uporabe goriva. Načrtovani izkoristki za glavne komponente so: kompresor in turbina (izentropno) 79,5% in 84,5%; generator in razsmernik: 92%. The cycle was studied using commercial process-simulation software integrated with a solid oxide fuel cell steady-state operation simulator that has been implemented using Fortran ([11] and [12]). The simulation model has been developed with the objectives of evaluating the performance of the system when varing: - operating temperature and pressure, - reactant gases composition, - fuel utilization coefficient. The assumed efficiency for the major components are: compressor and turbine (isoentropic) 79.5% and 84.5% respectively; generator and DC/ AC conversion: 92%. stran 585 R. Taccani: Kogeneracija z gorilnimi celicami - Co-Generation Using Fuel Cells Predhodni rezultati so predstavljeni na sliki 4 in sliki 5. Slika 4 prikazuje električni izkoristek in izkoristek po prvem glavnem zakonu v odvisnosti od kompresijskega razmerja. Največji električni izkoristek dobimo pri kompresijskem razmerju 4,3, in sicer je izkoristek 63,8%, medtem ko je izkoristek po prvem glavnem zakonu 83,1%. Ta električni izkoristek je zelo visok, če ga primerjamo z običajnimi sistemi proizvodnje elektrike, tudi večjimi. Na sliki 5 je prikazana izhodna moč v odvisnosti od kompresijskega razmerja. Kjer je električni izkoristek višji, je izhod toplote na minimumu. Nato se zopet Preliminary results are reported in Figure 4 and Figure 5. Figure 4 shows the electric and First Law efficiency as a function of the compression ratio. The maximum electric efficiency is obtained when operating at a compression ratio of 4.3 and it is 63.8%, while the First Law efficiency is 83.1%. This electric efficiency is very high when compared with any conventional power-generation systems, even those of larger size. In Figure 5 the system power output is plotted versus compression ratio. Where the electric efficiency is higher the heat output is at a minimum, and then increases again because the power system Sl. 4. TOGC - PT: Električni izkoristek, izkoristek po prvem glavnem zakonu v odvisnosti od kompresijskega razmerja Fig. 4. SOFC - GT: Electric efficiency, First Law efficiency as a function of the compression ratio kW 210 160 110 60 celotni električni izhod total electric output a A A A A -*¦* elektr a-------- FC ele električni izhod FC FC electric output V izhod toplote V^jheat output A i 1 3 5 7 9 11 13 15 kompresijsko razmerje / compression ratio Sl. 5. SOFC - GT: Električni izhod v odvisnosti od kompresijskega razmerja Fig. 5. SOFC - GT: Power outputs as a function of the compression ratio 00-8 VH^tTPsDDIK stran 586 R. Taccani: Kogeneracija z gorilnimi celicami - Co-Generation Using Fuel Cells zvišuje, ker je sistem opremljen s pomožnim gorilnikom, ki skrbi za stalno temperaturo vhodnih plinov v gorilno celico. Električna izstopna moč turbine je največja pri eni petini celotne moči. 5 SKLEP V prispevku je predstavljeno delovanje gorilne celice predvsem z vidika, da so gorilne celice ugodne za kogeneracijo v stavbah. Predstavljeni so nekateri sistemi. Predlagan je bil sistem s trdno oksidno gorilno celico in plinsko turbino, ki je bil simuliran z matematičnim modelom. Glavni rezultati tega dela so: - gorilna celica je idealna tehnologija za kogeneracijo v stavbah, - danes je samo en sistem kogeneracije na voljo na trgu, toda številni proizvajalci zatrjujejo, da bodo njihovi sistemi kmalu na voljo, - trdno oksidna gorilna celica se teoretično lahko poveže z mikroplinsko turbino, tako da proizvaja elektriko z visokim izkoristkom tudi pri manjših močeh, - izračunani električni izkoristek sistema je 63,8%. Sistemi TOGC in PT so zelo obetajoči tudi za stanovanjske enote, čeprav je treba ugotoviti možnost in trpežnost v primerjavi z običajnimi sistemi. Široka uporaba bo dala gorivnim celicam cenovno primerljivost z drugimi sistemi. Za gorilne celice že desetletja trdijo, da se bodo pocenile, toda čas za to še ni prišel. Potreba po gorilnih celicah v avtomobilski industriji in nizkoemisijskih vozilih naj bi vplivala na razvoj in možnost, da gorilne celice postanejo cenovno ugodne. Zahvala Hvaležen sem inž. Riccardu Valente-ju za sodelovanje in razvoj računalniškega programa za modeliranje sistema z TOGC in PT. is provided with an auxiliary burner in order to keep constant the temperature of the reactant gases entering the fuel cell. The turbine electrical output is at maximum of one fifth of the total power. 5 CONCLUSION In this paper the working principle of fuel cells has been briefly described, focusing on those aspects that make this technology attractive for residential co-generation. Some of the existing systems have been presented. Then a system based on solid-oxide fuel cells and a gas turbine has been proposed and analysed using a mathematical model. The main conclusions of this work are: - fuel cells seem to be one of the ideal technology for residential co-generation; - to date only one co-generative system has reached commercial maturity, but many manufacturers are now announcing the commercial availability of their products; - Solid-oxidef fuel cells can be well integrated, theoretically, with a micro gas turbine to yield high-efficiency power-generation cycles, even in the sub-MW power range; - the calculated electrical efficiency of the system is 63.8%. SOFC-GT systems seem to be very attractive even for residential-size power units, although reliability and durability comparable with conventional power plants and lower cost, essential to market entry, have still to be proved. However, their use will become widespread when they become cost-competitive. Fuel-cell advocates have been promising reductions in price for decades, but the time might actually be at hand. The need in the automotive industry for fuel cells in zero-emission vehicles may fuel an explosion in the technology development and manufacturing capability, finally bringing to reality the time of low-cost fuel cells. Acknowledgement I am very grateful to ing. Riccardo Valente for his decisive contribution to developing the computer program for modelling the SOFC-GT system. 6 LITERATURA 6 REFERENCES [1] Willis, H.L., W.G. Scott (2000) Distribuited power generation, Marcel Dekker, Inc, New York. [2] Stauffer, D.B., J.H. Hirschenhofer, R.R. Engleman, M.G. Klett (1998) Fuel cell hanbook, FETC. [3] Appleby, A.J, F.R. Foulkes (1989) Fuel cell handbook, Van Nostrand Reinhold, New York, NY. [4] Kordesch, K., G. Simader (1996) Fuel cells and their Application, VCH. [5] Ansaldo (1994) The PC25 Fuel cells co-generation power plant, CLC S.r.L., Genova, Italy. [6] Harvey, S.P., H.J. Richter (1994) Gas turbine cycles with solid oxide fuel cells, Part I: Improved gas turbine power plant efficiency by use of recycled exhaust gases and fuel cell technology. Journal of Energy Resources Technology, vol. 116. [7] Harvey, S.P., H.J. Richter (1994) Gas turbine cycles with solid oxide fuel cells, Part II: A detailed study of a gas turbine cycle with an integrated internal solid oxide fuel cells. Journal of Energy Resources Technology, vol. 116. stran 587 R. Taccani: Kogeneracija z gorilnimi celicami - Co-Generation Using Fuel Cells [8] Lubelli, F., A. F. Massardo (1998) Internal reforming solide oxide fuel cell-gas turbine combined cycles (IRSOFC-GT). Part A: cell model and cycle thermodynamic analysis. International Gas Turbine and Aeroengine Congress & Exhibition, Stockholm, Sweden. [9] Van Schie, N. (1995) Solide oxide fuel cell in combination with gas turbine. Netherland Energy research Foundation Report, ECN-I-95-020. [10] Campanari, S., S. Consonni, G. Lozza, E. Macchi (1998) Libro bianco sulla cogenerazione, Volume IV: “La micricogenerazione: le tecnologie del futuro, Associazione Termotecnica Italiana del Gas, Milano, December. [11] Valente, R. (2000) Modellizzazione d’ un impianto a celle a combustibile per la produzione combinata d’ energia elettrica e calore Master Thesis Universita` di Trieste [13] Achenbach, E. (1994) Three dimensional and time-dependent simulation of a planar SOFC stack. Journal of Power Sources, 49, 333-348. Medmrežje In the Web [W1] http://www.fuelcells.org [W2] http://www.northwestpower.com [W3] http://www.gefuelcell.com/homegen_prod_desc.html [W4] http://www.ballard.com Avtorjev naslov: Rodolfo Taccani Oddelek za energetiko Univerze v Trstu Via Valerio 10 34127 Trst, Italija Authors’ Address: Rodolfo Taccani Department of Energetics University of Trieste Via Valerio 10 34127 Trieste, Italy Prejeto: Received: 15.8.2000 Sprejeto: Accepted: 10.11.2000 00-8 VH^tTPsDDIK stran 588 © Strojni{ki vestnik 46(2000)8,589-590 ISSN 0039-2480 Navodila avtorjem © Journal of Mechanical Engineering 46(2000)8,589-590 ISSN 0039-2480 Instructions for Authors Navodila avtorjem Instructions for Authors Članki morajo vsebovati: - naslov, povzetek, besedilo članka in podnaslove slik v slovenskem in angleškem jeziku, - dvojezične preglednice in slike (diagrami, risbe ali fotografije), - seznam literature in - podatke o avtorjih. Strojniški vestnik izhaja od leta 1992 v dveh jezikih, tj. v slovenščini in angleščini, zato je obvezen prevod v angleščino. Obe besedili morata biti strokovno in jezikovno med seboj usklajeni. Članki naj bodo kratki in naj obsegajo približno 8 tipkanih strani. Izjemoma so strokovni članki, na željo avtorja, lahko tudi samo v slovenščini, vsebovati pa morajo angleški povzetek. Vsebina članka Članek naj bo napisan v naslednji obliki: - Naslov, ki primerno opisuje vsebino članka. - Povzetek, ki naj bo skrajšana oblika članka in naj ne presega 250 besed. Povzetek mora vsebovati osnove, jedro in cilje raziskave, uporabljeno metodologijo dela,povzetek rezulatov in osnovne sklepe. - Uvod, v katerem naj bo pregled novejšega stanja in zadostne informacije za razumevanje ter pregled rezultatov dela, predstavljenih v članku. - Teorija. - Eksperimentalni del, ki naj vsebuje podatke o postavitvi preskusa in metode, uporabljene pri pridobitvi rezultatov. - Rezultati, ki naj bodo jasno prikazani, po potrebi v obliki slik in preglednic. - Razprava, v kateri naj bodo prikazane povezave in posplošitve, uporabljene za pridobitev rezultatov. Prikazana naj bo tudi pomembnost rezultatov in primerjava s poprej objavljenimi deli. (Zaradi narave posameznih raziskav so lahko rezultati in razprava, za jasnost in preprostejše bralčevo razumevanje, združeni v eno poglavje.) - Sklepi, v katerih naj bo prikazan en ali več sklepov, ki izhajajo iz rezultatov in razprave. - Literatura, ki mora biti v besedilu oštevilčena zaporedno in označena z oglatimi oklepaji [1] ter na koncu članka zbrana v seznamu literature. Vse opombe naj bodo označene z uporabo dvignjene številke1. Oblika članka Besedilo naj bo pisano na listih formata A4, z dvojnim presledkom med vrstami in s 3 cm širokim robom, da je dovolj prostora za popravke lektorjev. Najbolje je, da pripravite besedilo v urejevalnilku Microsoft Word. Če uporabljate kakšen drug urejevalnik besedil, prosimo, da besedilo konvertirate v navadno ASCII (tekstovno) obliko. Hkrati dostavite odtis članka na papirju, vključno z vsemi slikami in preglednicami ter identično kopijo v elektronski obliki. Prosimo, da ne uporabljate urejevalnika LaTeX, saj program, s katerim pripravljamo Strojniški vestnik, ne uporablja njegovega formata. V urejevalniku LaTeX oblikujte grafe, preglednice in enačbe in jih stiskajte na kakovostnem laserskem tiskalniku, da jih bomo lahko presneli. Enačbe naj bodo v besedilu postavljene v ločene vrstice in na desnem robu označene s tekočo številko v okroglih oklepajih Enote in okrajšave V besedilu, preglednicah in slikah uporabljajte le standardne označbe in okrajšave SI. Simbole fizikalnih veličin v besedilu pišite poševno (kurzivno), (npr. v, T, n itn.). Simbole enot, ki sestojijo iz črk, pa pokončno (npr. ms 1, K, min, mm itn.). Papers submitted for publication should comprise: - Title, Abstract, Main Body of Text and Figure Captions in Slovene and English, - Bilingual Tables and Figures (graphs, drawings or photographs), - List of references and - Information about the authors. Since 1992, the Journal of Mechanical Engineering has been published bilingually, in Slovenian and English. The two texts must be compatible both in terms of technical content and language. Papers should be as short as possible and should on average comprise 8 typed pages. In exceptional cases, at the request of the authors, speciality papers may be written only in Slovene, but must include an English abstract. The format of the paper The paper should be written in the following format: - A Title, which adequately describes the content of the paper. - An Abstract, which should be viewed as a miniversion of the paper and should not exceed 250 words. The Abstract should state the principal objectives and the scope of the investigation, the methodology employed, summarize the results and state the principal conclusions. - An Introduction, which should provide a review of recent literature and sufficient background information to allow the results of the paper to be understood and evaluated. - A Theory - An Experimental section, which should provide details of the experimental set-up and the methods used for obtaining the results. - A Results section, which should clearly and concisely present the data using figures and tables where appropriate. - A Discussion section, which should describe the relationships and generalisations shown by the results and discuss the significance of the results making comparisons with previously published work. (Because of the nature of some studies it may be appropriate to combine the Results and Discussion sections into a single section to improve the clarity and make it easier for the reader.) - Conclusions, which should present one or more conclusions that have been drawn from the results and subsequent discussion. - References, which must be numbered consecutively in the text using square brackets [1] and collected together in a reference list at the end of the paper. Any footnotes should be indicated by the use of a superscript1. The layout of the text Texts should be written in A4 format, with double spacing and margins of 3 cm to provide editors with space to write in their corrections. Microsoft Word for Windows is the preferred format for submission. If you use another word processor, please convert to normal ASCII (text) format. One hard copy, including all figures, tables and illustrations and an identical electronic version of the manuscript must be submitted simultaneously. Please do not use a LaTeX text editor, since this is not compatible with the publishing procedure of the Journal of Mechanical Engineering. Graphs, tables and equations in LaTeX may be supplied in good quality hard-copy format, so that they can be copied for inclusion in the Journal. Equations should be on a separate line in the main body of the text and marked on the right-hand side of the page with numbers in round brackets. Units and abbreviations Only standard SI symbols and abbreviations should be used in the text, tables and figures. Symbols for physical quantities in the text should be written in Italics (e.g. v, T, n , etc.). Symbols for units that consist of letters should be in plain text (e.g. ms-1, K, min, mm, etc.). stran 589 glTMDDC Strojni{ki vestnik - Journal of Mechanical Engineering Vse okrajšave naj bodo, ko se prvič pojavijo napisane v celoti, npr. časovno spremenljiva geometrija (ČSG , . Slike Slike morajo biti zaporedno oštevilčene in označene, v besedilu in podnaslovu, kot sl. 1, sl. 2 itn. Posnete naj bodo v kateremkoli od razširjenih formatov, npr. BMP, JPG, GIF. Za pripravo diagramov in risb priporočamo CDR format (CorelDraw), saj so slike v njem vektorske in jih lahko pri končni obdelavi preprosto povečujemo ali pomanjšujemo. Pri označevanju osi v diagramih, kadar je le mogoče, uporabite označbe veličin (npr. t, v, m itn.), da ni potrebno dvojezično označevanje. V diagramih z več krivuljami, mora biti vsaka krivulja označena. Pomen oznake mora biti pojasnjen v podnapisu slike. Vse označbe na slikah morajo biti dvojezične. Za vse slike po fotografskih posnetkih je treba priložiti izvirne fotografije ali kakovostno narejen posnetek. V izjemnih primerih so lahko slike tudi barvne. Preglednice Preglednice morajo biti zaporedno oštevilčene in označene, v besedilu in podnaslovu, kot preglednica 1, preglednica 2 itn. V preglednicah ne uporabljajte izpisanih imen veličin, ampak samo ustrezne simbole, da se izognemo dvojezični podvojitvi imen. K fizikalnim veličinam, npr. t (pisano poševno), pripišite enote (pisano pokončno) v novo vrsto brez oklepajev. Vsi podnaslovi preglednic morajo biti dvojezični. Seznam literature Vsa literatura mora biti navedena v seznamu na koncu članka v prikazani obliki po vrsti za revije, zbornike in knjige: [1] Tarng, Y.S., Y.S. Wang (1994) A new adaptive controler for constant turning force. Int J Adv Manuf Technol 9(1994) London, pp. 211-216. [2] Čuš, F., J. Balič (1996) Rationale Gestaltung der organisatorischen Ablaufe im Werkzeugwesen. Proceedings of International Conference on Computer Integration Manufacturing Zakopane, 14.-17. maj 1996. [3] Oertli, PC. (1977) Praktische Wirtschaftskybernetik. Carl Hanser Verlag Minchen. Podatki o avtorjih Članku priložite tudi podatke o avtorjih: imena, nazive, popolne poštne naslove, številke telefona in faksa ter naslove elektronske pošte. Sprejem člankov in avtorske pravice Uredništvo Strojniškega vestnika si pridržuje pravico do odločanja o sprejemu članka za objavo, strokovno oceno recenzentov in morebitnem predlogu za krajšanje ali izpopolnitev ter terminološke in jezikovne korekture. Avtor mora predložiti pisno izjavo, da je besedilo njegovo izvirno delo in ni bilo v dani obliki še nikjer objavljeno. Z objavo preidejo avtorske pravice na Strojniški vestnik. Pri morebitnih kasnejših objavah mora biti SV naveden kot vir. Rokopisi člankov ostanejo v arhivu SV Vsa nadaljnja pojasnila daje: Uredništvo STROJNIŠKEGA VESTNIKA p.p. 197/IV 1001 Ljubljana Telefon: (061) 1771-428 Telefaks: (061) 218-567 E-mail: strojniski.vestnik@fs.uni-lj.si All abbreviations should be spelt out in full on first appearance, e.g., variable time geometry (VTG). Figures Figures must be cited in consecutive numerical order in the text and referred to in both the text and the caption as Fig. 1, Fig. 2, etc. Figures may be saved in any common format, e.g. BMP, GIF, JPG. However, the use of CDR format (CorelDraw) is recommended for graphs and line drawings, since vector images can be easily reduced or enlarged during final processing of the paper. When labelling axes, physical quantities, e.g. t, v, m, etc. should be used whenever possible to minimise the need to label the axes in two languages. Multi-curve graphs should have individual curves marked with a symbol, the meaning of the symbol should be explained in the figure caption. All figure captions must be bilingual. Good quality black-and-white photographs or scanned images should be supplied for illustrations. In certain circumstances, colour figures may be considered. Tables Tables must be cited in consecutive numerical order in the text and referred to in both the text and the caption as Table 1, Table 2, etc. The use of names for quantities in tables should be avoided if possible: corresponding symbols are preferred to minimise the need to use both Slovenian and English names. In addition to the physical quantity, e.g. t (in Italics), units (normal text), should be added in new line without brackets. All table captions must be bilingual. The list of references References should be collected at the end of the paper in the following styles for journals, proceedings and books, respectively: [1] Tarng, Y.S., Y.S. Wang (1994) A new adaptive controler for constant turning force. Int J Adv Manuf Technol 9(1994) London, pp. 211-216. [2] Čuš, F., J. Balič (1996) Rationale Gestaltung der organisatorischen Ablaufe im Werkzeugwesen. Proceedings of International Conference on Computer Integration Manufacturing Zakopane, 14.-17. maj 1996. [3] Oertli, PC. (1977) Praktische Wirtschaftskybernetik. Carl Hanser Verlag Minchen. Author information The following information about the authors should be enclosed with the paper: names, complete postal addresses, telephone and fax numbers and E-mail addresses. Acceptance of papers and copyright The Editorial Committee of the Journal of Mechanical Engineering reserves the right to decide whether a paper is acceptable for publication, obtain professional reviews for submitted papers, and if necessary, require changes to the content, length or language. Authors must also enclose a written statement that the paper is original unpublished work, and not under consideration for publication elsewhere. On publication, copyright for the paper shall pass to the Journal of Mechanical Engineering. The JME must be stated as a source in all later publications. Papers will be kept in the archives of the JME. You can obtain further information from: Editorial Board of the JOURNAL OF MECHANICAL ENGINEERING P.O.Box 197/IV 1001 Ljubljana, Slovenia Telephone: +386 (0)61 1771-428 Fax: +386 (0)61 218-567 E-mail: strojniski.vestnik@fs.uni-lj.si 00-8 VH^tTPsDDIK stran 590