Abstract:The asymmetric influence of the volute on the flow in a transonic, high-pressure ratio centrifugal compressor at off-design conditions was investigated. Fully three-dimensional viscous steady-state computational fluid dynamics (CFD) was applied to simulate the flow in a 4.2:1 design pressure ratio compressor for automotive application. Computed performance characteristics are presented for low-and high-pressure ratio operating conditions, with and without an overhung volute. The volute was found to severely harm aerodynamic stability of the investigated compressor when operating at lower than design mass flow. The relative narrowing effect of the volute on compressor map width increases with pressure ratio up to a 42 per cent drop in stable flow range at design speed. The inter-passage variations in performance quantities and the influence of the volute tongue region are discussed in detail. The circumferential variations of incidence angle correlate with rotational speed, which, in combination with the higher sensitivity to incidence angle at transonic inflow conditions, seems to deteriorates stability when transonic inflow conditions are reached.

R32 has been considered as an important alternative in the phase-out of hydrochlorofluorocarbons (HCFCs) due to its advantages such as relatively low global warming potential compared to R410A, favorable thermal properties. However, the increased discharge temperature of the R32 compressor, compared with R410A, is the main barrier affecting the wide and quick adoption. In this work, three promising methods to decrease the discharge temperature of R32 scroll compressor, namely, two-phase suction, liquid injection and two-phase injection, have been investigated. By considering the variations of motor efficiency and leakage rate, an improved distributed parameter model of the scroll compressor is rebuilt based on a previously developed one (Wang et al., 2008). By that model, the effectiveness of these three methods in decreasing discharge temperature and their influence on thermodynamic performance are researched.It is concluded that all the three methods show excellent potential in decreasing the discharge temperature of R32 scroll compressor. Besides, two-phase injection outperforms the other two methods in cooling capacity and COP by 11.8% and 4.8%, respectively.

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