Simulation study of a CO₂ scroll compressor with main and pre-discharge valves.

The over-compression phenomenon in CO₂ scroll compressors, compared to those using conventional refrigerants, significantly impairs performance. To address this issue, a three-dimensional simulation model of a CO₂ scroll compressor incorporating pre-discharge valves was developed to mitigate the impact of the overcompression phenomenon on compressor performance. Simulation results indicate that, compared to scroll compressors without a pre-discharge valve (NPDV) structure, those with a pre-discharge valve (PDV) structure exhibits a reduction of 4.4 MPa in the maximum pressure and 25 K in the maximum temperature within the compression chamber. The range of the over-compression effect has been reduced from 251 - 425◦to 373 - 425◦, and the pre-compression phenomenon is improved. Additionally, the pre-discharge valve structure reduces the impact of the gas on the main discharge valve. It also decreases both the axial and radial clearance gas leakage velocities, with the average mass flow rate of axial clearance leakage reduced by 12 %. As a result of the predischarge valve structure, the inlet mass flow rate increases by 4.2 % and the volumetric efficiency improves by 3.2 %. Moreover, the discharge temperature, torque, and shaft power of the scroll compressor are reduced by 5 K, 1.39 N⋅m, and 99 W, respectively.