Theoretical performance comparison for two-stage auto-cascade refrigeration system using hydrocarbon refrigerants.

• Performance of a two-stage ARC system using R170/R600a, R170/R600, R1150/R600a, R1150/R600, and R23/R134a was compared. • Under different working conditions, the variation of the maximum COP with the optimal refrigerant ratio was investigated. • R170/R600 afforded the best performance to replace R23/R134a in the ARC system. • Under certain working condition, the exergy loss ratio of each component in the ARC system was analyzed. Auto-cascade refrigeration cycle (ARC) is widely used in low-temperature applications. The selection and proportion of refrigerant mixtures in an ARC system have a significant impact on the environment and system performance. In this study, the theoretical performance of a two-stage ARC system using R170/R600a, R170/R600, R1150/R600a, R1150/R600, and R23/R134a was compared. The results showed that, under certain working conditions in the ARC, an optimal refrigerant ratio maximized the COP of the system. At lower evaporator outlet temperatures or higher condenser outlet temperatures, the performance of the system using R170/R600a, R170/R600, R1150/R600a, and R1150/R600 offers advantages over that when using R23/R134a. Among these, R170/R600 afforded the best performance. Exergy analysis was also performed, and the exergy loss ratios of the heat exchanger in the R170/R600 and R23/R134a systems were the highest at 52.3% and 56.7%, respectively. [ABSTRACT FROM AUTHOR]