Cooling performance of several CO2/propane mixtures and glide matching with secondary heat transfer fluid

This paper presents the cooling performance of several CO2/propane mixtures measured in air-conditioning test rig at several conditions. The discharge pressure of CO2/propane mixtures is reduced with increasing mole fraction of propane and their reduced values coincide approximately with the circulation concentrations of propane. Since propane is the refrigerant having a higher refrigerating effect and a much lower vapor density than CO2, adding propane to CO2 improves the system efficiency and reduces the cooling capacity. The temperature glide effect of CO2/propane mixtures on the cooling performance was analyzed based on the experimental data. To utilize the temperature glide effect successfully, a sufficient heat exchange area is required, and the temperature gradient of refrigerant must be similar to that of secondary heat transfer fluid. It is better the temperature change of refrigerant can prevent pinching with that of the secondary heat transfer fluid.