© Strojni{ki vestnik 49(2003)2,90-99 ISSN 0039-2480 UDK 621.564:621.565 Izvirni znanstveni ~lanek (1.01) © Journal of Mechanical Engineering 49(2003)2,90-99 ISSN 0039-2480 UDC 621.564:621.565 Original scientific paper (1.01) Eksperimentalno presku{anje prenosa toplote v Lorenzovem postopku z uporabo zeotropnih zmesi Experimental Testing of the Heat Transfer in a Lorenz Process Using Zeotropic Mixtures Vladimir Soldo - Tonko ]urko - Vlasta Zanki Za sistem, ki deluje pri enakih pogojih je bila opravljena primerjava med termodinamičnim izkoristkom za enokomponentno hladivo R22 ter za njegovo zamenjavo z zeotropno zmesjo R407C. Predstavljena je konstrukcija hladilnega sistema, ki omogoča delovanje z R22 ter R407C, skupaj z meritvami vseh ustreznih podatkov (temperatura, tlak in pretok), njihovim zapisom ter analizo. Dobljeni rezultati kažejo, da je hladivo R407C dobra zamenjava za R22 pri višjih temperaturah uparjanja. Čeprav so teoretični rezultati vodili k predpostavki, da bo R407C v primerjavi z R22 povečal izkoristek, tega eksperimentalni rezultati niso potrdili. Razlog za to dejstvo je v nižjih toplotnih prestopnostih v primeru uporabe hladiva R407C. © 2003 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: zmesi zeotropske, procesi Lorentz, izkoristki termodinamični, prenos toplote) A comparison has been made between the thermodynamic efficiency of a single-component refrigerant R22 and a substitute zeotropic mixture R407C in a system operating under the same conditions. The construction of a refrigerating system that uses R22 and R407C is presented, along with measurements of all the relevant data (temperature, pressure and flow rate), their acquisition, and their analysis. Our results show that the refrigerant R407C is a good substitute for the refrigerant R22 at higher evaporation temperatures. Although the theoretical results suggest that R407C will increase efficiency compared to R22, the experimental results did not confirm it. This because in the process with the refrigerant R407C the heat-transfer coefficients are lower. © 2003 Journal of Mechanical Engineering. All rights reserved. (Keywords: zeotropic mixtures, Lorentz process, thermodynamic efficiency, heat transfer) 1 DEFINICIJA PROBLEMA Teoretične in eksperimentalne študije so pokazale, da lahko termodinamični izkoristek hladilnega sistema izboljšamo z uporabo zeotropnih zmesi [1]. Zeotropne zmesi so uporabljene tako, da se povečanje temperature med uparjanjem ujema s hlajenim sredstvom, oziroma da se zmanjšanje temperature pri kondenzaciji ujema s temperaturo okolice in tako omogočajo Lorenzov postopek. Torej glede na Lorenzov postopek je tu največja prednost hladilnega postopka (celo večja kakor pri Carnotovem postopku) ta, da se ta postopek najbolj učinkovito prilagaja temperaturnim spremembam hlajenega sredstva ali okolice. Slika 1 daje kakovostno predstavo Carnotovega in Lorenzovega procesa pri enakih 1 PROBLEM DEVELOPMENT Theoretical and experimental studies have shown that the thermodynamic efficiency of a refrigerating system can be improved by using a zeotropic mixture [1]. Zeotropic mixtures are used in such a way that the temperature increase during evaporation coordinates with the cooled medium, while at the same time the temperature decrease of the condensation coordinates with the temperature medium of the environment, and in this way the Lorenz process is enabled. According to Lorenz, the most advantageous refrigerating process, even more advantageous than Carnot’s process, would be the one that is the most effectively adapted to the temperature changes of the cooled medium, or to the medium of the environment. Figure 1 gives a qualitative presentation of the Carnot and Lorenz processes for the same grin^SfcflMISDSD VBgfFMK stran 90 Soldo V., ]urko T., Zanki V.: Eksperimentalno testiranje - Experimental Testing T hladivo refrigerant odvod toplote heat vir toplote heat source refriger^L odvod toplote heat sink ~ LORENZ heat source Sl. 1. Kakovostna primerjava Carnotovega in Lorenzovega postopka v diagramu T-s Fig. 1. Qualitative comparison of the Carnot and Lorenz processes, presented on T-s diagrams temperaturah toplotnega vira in ponora. Šrafirana površina predstavlja izgubo eksergije v prenosnikih toplote. Če gledamo sliki, je očitno, da bo Lorenzov postopek termodinamično bolj učinkovit, toda pod pogojem, da prenos toplote poteka v protitočnih prenosnikih toplote z majhno temperaturno razliko. 2 EKSPERIMENTALNA OPREMA IN MERITVE Slika 2 opisuje eksperimentalno opremo s hladilnim sistemom, ki omogoča obratovanje sistema po Lorenzovem (uporaba zeotropne zmesi) ter Carnotovem postopku (uporaba azeotropne zmesi ter čistega hladiva). Osnovni elementi sistema so polzaprti batni kompresor, protitočni uparjalnik cev v cevi, kondenzator in termoekspanzijski ventil. Sistem je opremljen z inštrumenti in zaznavala, ki merijo vse ustrezne parametre (temperatura, tlak in pretok) in so povezani z zapisovalnikom podatkov ter analizatorjem ([2] in [3]). 3 ANALIZA REZULTATOV MERITEV Opravljena je bila primerjava rezultatov meritev med postopkom s čistim hladivom R22 in med postopkom z zeotropno zmesjo R407C. Preskus na hladilnem sistemu sestoji iz meritev temperature na vstopu in izstopu hladiva iz prenosnika, hladiva in hladilne vode, meritev pretoka v primarni zanki in v obeh sekundarnih zankah, tlaka uparjanja in kondenzacije ter električne moči motorja kompresorja. Izmerjene temperature, tlaki in vrednosti pretokov so obdelani s programom LabVIEW, ki uporablja kot vir program bazo podatkov REFPROP ([4] in [5]) za izračun termodinamičnih in fizikalnih temperature of heat source and heat sink. The hatched surface represents the exergy loss on the heat exchangers. It is obvious from the figures that the Lorenz process will be thermodynamically more efficient, but on condition that the heat transfer takes place in counter-flow heat exchangers with a small driving temperature difference. 2 EXPERIMENTAL RIG AND MEASUREMENTS Figure 2 is a schematic diagram of the experimental rig with a refrigerating system that can operate according to the Lorenz (zeotropic mixture application) and Carnot (application of azeotropic mixture and pure refrigerant) processes. The basic system elements are a semi-hermetic reciprocating compressor, a counterflow tube-in-tube evaporator, a condenser and a thermoexpansion valve. The system is equipped with instruments and sensors that measure all the relevant data (temperature, pressure and flow rate), and is connected to a data-acquisition and analysis system ([2] and [3]). 3 ANALYSIS OF THE MEASUREMENT RESULTS A comparison between the process with the pure refrigerant R22 and the process with the zeotropic mixture R470C was carried out. The experiment on the refrigerating system con-sists of temperature measurements, at the exchanger in-lets and outlets, of the refrigerant, the coolant and cool-ing water, flow measurements in the primary loop and in both secondary loops, evaporation and condensation pressure and the electric power of the compressor motor. The measured temperature, pressure and flow values are processed using the LabVIEW program, which uses the source program REFPROP databank ([4] and [5]) for the refrigerant’s thermodynamic and gfin^OtJJlMlSCSD stran 91 T Soldo V., ]urko T., Zanki V.: Eksperimentalno testiranje - Experimental Testing Izpust hladilne vode Discharge of cooling water i-------->------txi- T -Xh Dovod vode Water supply,.. r —% X