The domestic and international investigations on CO2 gas cooler with different forms were summarized. The performance of three kinds of tube-in-tube gas coolers

plain tube

rectangular spiral tube and circular spiral tube were simulated. The heat transfer amount of unit pressure drop was put forward to evaluate the gas cooler performance in the supercritical condition. According to the simulated result

a set of tube-in-tube gas cooler with rectangular spiral tube was designed and the influences of CO2 inlet pressure

inlet water flowrate and temperature on heat transfer coefficient

heat transfer amount

COP and heat exchanger efficiency were studied experimentally. The results show that the system COP can reach 2.85 when CO2 inlet pressure is 8 MPa

inlet water flowrate is 1.56 kg/min and inlet water temperature is 9 ℃. The results can provide reference for the practical application of the CO2 heat pump water heater.