The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation Rate for Refrigeration Cycles

This paper investigates the effect of heat exchanger allocation on overall system performance using both reverse Carnot and vapor compression refrigeration cycle models to calculate system performance and entropy generation rate. The algebrai­ cally simple constraints applied in previous studies are shown to be justifiable. The vapor compression model considers nonideal compressor performance, compressor volumetric efficiency, refrigerant properties, and throttling, in addition to mechanistic heat exchanger models. The results support the conclusions of previous studies in that maximum performance is observed when the condenser and evaporator thermal sizes are approximately equal. For air-to-air systems, this result indicates that the areas of the heat exchangers should be approximately equal. However, it is found that minimizing the entropy generation rate does not always result in the same design as maximizing the system performance unless the refrigeration capacity is fixed. Minimizing the entropy generation rate per unit capacity is found to always corre­ spond to maximizing the coefficient of performance of refrigeration systems.