A Rolling Piston-Type Two-Phase Expander in the Transcritical CO2 Cycle

Although the application of the CO2 cycle to refrigeration and air conditioning can be good for the environment, it can also be inefficient. To improve the efficiency of the cycle, new devices must be developed, such as a CO2 rolling piston-type expander that can take the place of the throttling valve in the system to recover power during the expansion process. The parameters Of the rolling piston-type expander (e.g., mass flow rate and the volume of the cylinder, the suction port, and the discharge port) were analyzed and designed. The experimental prototype was constructed and tested. The expander replaced the throttling valve in the experimental Transcritical CO2 water-source heat pump. The experimental results showed that the suction control system and the expander could work normally. The expander, having measured isentropic efficiency up to 58.7%, increased the cooling coefficient of performance (COP) up to at least 10% at tested conditions.