R32/R134a自复叠热泵变组分浓度实验分析OA北大核心CSTPCD

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.