NONAZEOTROPIC MIXTURES AS WORKING FLUIDS IN 2-STAGE ECONOMIZER-TYPE HEAT-PUMPS

The thermodynamic differences in behaviour between non-azeotropic mixt ures and pure fluids in two-stage cycles are theoretically investigate d for two applications and over the whole composition range of three m ixture pairs, HCFC22 HFC152a, HCFC22-HCFC142b and HCFC22-CFC114. The t wo most common types of two-stage plant are covered: those working wit h a flash vessel at an intermediate pressure, and those in which an ec onomizer heat exchanger is used. The coefficient of performance (COP) and the capacity of the two types with different working fluids are co mpared with each other as well as with the performances of a one-stage cycle. It is found that the COP and the capacity of a non-azeotropic mixture increase more than those of a pure fluid upon changing from a one-stage cycle to a two-stage cycle with economizer heat exchanger. I n the search for the 'best' working fluid, pure or a mixture, for a gi ven application, the optimal choice depends on which type of cycle one intends to use.