Performance analysis of a modified autocascade refrigeration cycle with an additional evaporating subcooler

A modified autocascade refrigeration cycle with an additional evaporating subcooler is proposed, which can make good use of the temperature glide characteristic of zeotropic mixtures. The energy and exergy performance comparison between the modified cycle and a basic autocascade refrigeration cycle using the zeotropic mixture of R23/R134a is carried out by the simulation method. Under the considered operating conditions, the coefficient of performance (COP), volumetric cooling capacity and exergy efficiency of the modified cycle can be improved by up to an average of 37.5%, 42.3% and 34.3% compared to that of the basic cycle, respectively. Within a certain subcooling range, the performance of the modified cycle will be improved with increasing the subcooling degree in the evaporating subcooler. In addition, the increase of the vapor quality at the condenser outlet not only leads to the performance improvements of two cycles but also results in the increase of the working pressure ratio and discharge temperature of the compressor. A similar situation also occurs for the performance variations of two cycles with the mass fraction of the zeotropic mixture.