Auto-refrigerating cascade (ARC) systems possess many advantages comparing with traditional cascade refrigeration systems. This work proposed a novel ternary mixture, R600a/R23/R14, for ARC systems for 190K applications. The performance of the ternary mixture and the influences of compositional ratio and bypass scheme were assessed in a modified domestic cooler. The results demonstrated the feasibility of the proposed R600a/R23/R14 ternary mixture as an environmental benign alternative for ARC systems. The performance varied little within a certain composition range and a mass ratio of 35/30/35 for R600a/R23/R14 mixture was recommended. It also showed that the two bypass schemes, which can regulate more effectively the refrigerant compositions, were better than the conventional hot-gas bypass approach. The variation of the evaporator temperature suggested the presence of local dryout at high heat loads (i.e., larger than the design value), which should be carefully prevented.

Thermodynamic properties of zeotropic mixtures of R600a/R23/R14 have been investigated and calculated based on the established mathematical model. The deviations of bubble pressure and vapor composition between the simulation results and the experimental data were 20.16% and 21.22% for R600a/R23 and 20.14% and 0.5% for R134a/R23, respectively. The simulation results of R32/R125/R134a were compared with the experimental values of the component, and the average error was 0.31%, and most deviations were within 6 5%. The average error in enthalpy value and entropy value between the simulation and National Institute of Standard Technology data was 20.25% and 3.33%, respectively. This suggests that the simulation results meet the requirements of engineering calculation. Based on the experimental results, the thermodynamic properties of the auto-cascade refrigeration system were calculated and analyzed in detail. The pressure-enthalpy diagrams of the auto-refrigerating cascade system with R600a/R23/R14 under the operating conditions were given, and the cycle of this system can be clearly described by the diagram of spatial pressure-enthalpy, which indicates that this simulation program could analyze the system cycle effectively and provide a direction for improvement of the auto-refrigerating cascade system.

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The condensing and evaporating characteristics of an auto-refrigerating cascade cycle employing ternary zeotropic mixture R600a/R23/R14 are studied in this article. When the outlet temperature of condenser is 300 K, the composition ratio of R600a/R23/R14 in liquid mixture is 78.04/12.62/9.34, respectively. In the liquid mixture, the R600a is the dominating component. The separation mass fraction of R23 by phase separators I and II is 12.62% and 30.27%, respectively; 78.04% refrigerant R600a can be separated by phase separator I, and 9.34% refrigerant R14 is liquid. In evaporator, the composition ratio of R600a occupies 6.31%, while the low-boiling-point refrigerant R14 accounts for 45.64%. The changing of composition ratio could significantly influence the cooling loads while had a little influence on the changing of the evaporating temperature. The maximum cooling load is 85 and 50 W for composition 35/35/30 and composition 35/30/ 35, respectively, and the maximum coefficients of performance are 14.4% and 8.5%, respectively.