Carbon dioxide (CO2) as a natural refrigerant is one candidate alternative to HFC refrigerants. But CO2 system has lower efficiency and is not yet competitive concerning the COP. The most effective method to improve the efficiency of the transcritical CO2 system is to replace the throttling device with an expander. In this paper, a two-cylinder rolling piston expander without inlet valve has been developed. In order to understand the work process of this expander, the prototypes installed with sensors have been made, and a test rig for the expander was built. The working performance were tested at different operating conditions, and the results were analyzed.
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