Study Of An Air-source Transcritical CO₂Heat Pump Water Heater System Performance

CO2heat pump water heater is a water heating device through using special physical property of supercritical CO2. Compared with the conventional water heaters, CO2heat pump water heaters are more environmentally friendly, safe and efficient, and can heat the water above90℃. In Japan, the CO2heat pump water heater has been used in the family as a commercial product, while the applications and performance optimizations of the CO2heat pump water heaters should be further studied in our country. To study the cyclic performance of CO2heat pump water heaters and provide a certain theoretical and experimental basis for being used, the concrete research contents are displayed as follows:Setting up a CO2heat pump water heater circulation device and calculating its cycle parameters.Investigating the effects of evaporation temperature, the inlet temperature of water, the cooling pressure and the volume flow of water on COP, the exhaust temperature of the compressor, the outlet temperature of water and the pressure drop of the gas cooler, which provides a good theoretical basis for the optimization of the system. The result shows that the CO2heat pump can heat the water above95℃, what’s more, the maximum value of the COP is about4.18.The three-dimensional model of the gas cooler is established with CFD software to simulate the heat transfer process of ScCO2in the gas cooler and the temperature distributions of CO2in the gas cooler with different cooling pressures and heat fluxes are acquired. The paper also shows the changes of Nu and h along the length of the tube with different cooling pressures and heat fluxes. The results show that when the inlet pressure changes from7.5MPa to9.5MPa, the Nu of the entrance increases from404to806and h increases from2769to6149; when the heat fluxes changes from10245w/m2to32835w/m2, Nu of the entrance increases from695to919and h increases from5244to6914.According to the experimental results, a new heat transfer correlation is obtained through modifying the classic Dittus-Boelter heat transfer correlation, and the experimental results agree well with the calculated results.