Zeotropic mixture; Vapor Injection; Multi-stage; Thermodynamic;
This paper mainly focuses on the vapor compression cycle performance improvement by using zeotropic mixtures as a working fluid, and applying a multi-stage cycle technology. The refrigerants used in the previous studies are mostly pure fluids (e.g. R134a) and azeotropic mixtures (e.g. R410A), while little attention has been paid on zeotropic mixtures. Zeotropic mixture can improve the cycle performance by reducing the temperature difference between two fluids in heat exchangers. And the multi-stage cycle technology can improve the cycle performance by reducing compression and expansion losses. In this paper, these two concepts are applied and their effects are investigated. A comparison study between pure refrigerants and binary zeotropic mixtures is conducted based on the two-stage vapor injection cycle. The effect of the mixture composition on the irreversibility loss generated in each thermodynamic process is studied. Then, the number of vapor injection to the compressor is varied and its theoretical limit is discussed. The slop of the saturated vapor line in temperature-entropy diagram (T-s) is investigated for the performance limitation.