CALCULATION METHODS FOR COMPARING THE PERFORMANCE OF PURE AND MIXED WORKING FLUIDS IN HEAT-PUMP APPLICATIONS

Three methods for comparing cycle Performance of working fluids. pure as well as non-azeotropic mixtures. are investigated for two applicati ons and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating th e heat exchange processes. They assume, respectively. equal minimum ap proach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with comp osition arc explained for all methods. It is shown that transport prop erties must be taken into account when making rigorous comparisons bet ween working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be est imated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided f or non-azeotropic mixtures.