Thermodynamics and flow unsteadiness analysis of trans-critical CO2 in a scroll compressor for mobile heat pump air-conditioning system

Heat pump air-conditioning system operating with trans-critical CO2 is a promising technology on electric vehicles, and scroll compressor has played a vital role in micro heat pump air-conditioning system. In order to obtain a better performance of scroll compressor for CO2, internal flow characteristics should be investigated. In this paper, an unsteady Reynolds Average Navier-Stokes of working process in a scroll compressor operating with trans-critical CO2 was firstly carried out. The effect of CO2 properties tables resolution on numerical simulation was investigated in detail. Then, some phenomena including pre-compression and over-compression in the working process were presented. Finally, physical mechanisms of asymmetric leakage flow considering influence of aerodynamics and thermodynamics were revealed. The results indicated that CO2 properties tables resolution hardly affects simulation results considering fierce fluctuations of CO2 properties near critical point. Periodic pre-compression and over-compression was mainly induced by geometrical structure and operation mechanism of scroll compressor. Asymmetric flow fields in circumferential direction were also observed due to unilateral inlet and orbiting scroll rotation. Meanwhile, so-called quasi-centrosymmetric leakage flow was captured in compression chambers owing to the non-uniform distribution of flow field. The results provide an instrumental guidance for optimal design of trans-critical CO2 scroll compressor.