The study on mass transport process in the cylinder of CO₂ compressor based on p-V diagram

Ways to properly enhance the performance of a transcritical CO₂ refrigeration system is a hot topic. The internal mass transport process in the reciprocating compressor has a significant influence on the performance of a transcritical CO₂ refrigeration system. In this paper, a thermodynamic model of a transcritical CO₂ compressor is derived from the experimental p-V diagram in the expansion and compression phases. Based on this model, a novel measurement method for the mass of CO₂ in the cylinder is proposed, which can effectively analyze the CO₂ transport process in the cylinder. The result shows the residual mass of CO₂ in the clearance volume is closely related to the delayed closing time of the discharge valve and the rotational speed. Furthermore, the method can be used to calculate the mass flow rate of CO₂. Compared with the measurement results of the flowmeter, the error of this method is within ±5.2% under various rotational speeds and operating conditions.