Experimental study on concentration control of variable components in auto-cascade heat pumps using R32/R134a
To solve performance degradation problems of heat pumps under conditions of large operating temperature difference between source and supply waters,a novel auto-cascade heat pump was proposed and tested with a mixed refrigerant of R32 and R134a.The variation of component distribution was experimentally investigated to assess its effects on the system performance.The test results show that the low-boiling component R32 mass fraction dropped by 2.5%-8.1%with the increase of the condenser outlet water temperature and the first electrical expansion valve opening.Moreover,charging more mixed refrigerant could contribute to a lower system discharge temperature and increase the low-boiling component R32 mass fraction at the main cycle.When the system worked with 2.8 kg mixed refrigerant at the condenser outlet water temperature of 65℃,the system COP achieved~2.22,and the compressor discharge temperature can be controlled under 80℃.Meanwhile,the discharge temperature droped by up to 25.4%when increasing the low-boiling component R32 mass fraction from 0.3 to 0.5.Compared with the single-stage vapor compression system,the proposed auto-cascade system presents a perfect performance and lowers the discharge temperature by about 31.2%at the same working condition.This result indicates that the component distribution control of the mixed refrigerant could effectively improve the system performance and contribute to long-term stability and energy-saving.
auto-cascade heat pumpnon-azeotropic refrigerantvariable component concentrationexperimental research