2ND-LAW-BASED THERMODYNAMIC ANALYSIS OF 2-STAGE AND MECHANICAL-SUBCOOLING REFRIGERATION CYCLES

Thermodynamic analysis of HFC-134a vapor-compression refrigeration cyc les is investigated by both the first and second laws of thermodynamic s. Second-law analysis is carried out for both two-stage and mechanica l-subcooling refrigeration cycles. The analysis is performed on each o f the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the l osses are due to a low compressor efficiency. Irreversibilities of exp ansion valves and condenser are also significant. In addition, it is s hown that the optimum inter-stage pressure for two-stage and mechanica l-subcooling refrigeration systems is very close to the saturation pre ssure corresponding to the arithmetic mean of the refrigerant condensa tion and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results o f a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. Copyright (C) 1996 Elsevier S cience Ltd and IIR