Experimental studies on mixture of carbon dioxide and propane as working fluid in heat pump system

Binary blend of CO2 with R290 is proposed in this paper to reduce the heat rejection pressure for pure CO2, and meanwhile weaken the flammability and explosivity for pure R290. Then, the system performances of heat pump using mixture of CO2 and R290 were experimentally studied when R290 is added into CO2 with a small majority, and compared with the pure CO2. The experimental testing is designed and set up for the transcritical heat pump system. When the refrigerant charge is variable, the heating coefficient performance, optimum heat rejection pressure, compressor power, mass flow rate of refrigerant, and total heat coefficient for gas cooler were researched. The variation ratios of heating coefficient performance and heating capacity with deviation from optimum refrigerant charge were also investigated. The optimum refrigerant charge of CO2/R290 is obtained and the research results show that the addition of R290 to CO2 can reduce the heat rejection pressure and improve the system performance.