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.