The multiway valve is the core component of the integrated thermal management system in an electric vehicle, and its heat transfer loss and pressure loss significantly impact the performance of the whole thermal management system. In this paper, heat transfer loss and pressure loss in multiway valves are investigated using three-dimensional unsteady numerical simulations. Heat transfer loss and pressure loss under different operating modes are revealed, and relationships between pressure loss and mass flow rate, inlet temperature, and valve materials are studied. The results show that the significant temperature gradient around the control shaft results in heat transfer loss and pressure loss mainly occurs around the junction of the control shaft and the shell, where the flow direction changes sharply. The pressure loss is nonlinearly and positively correlated with the mass flow rate. Furthermore, the main geometric parameters of the pipeline and the control shaft are optimized. The pressure loss firstly increases and then decreases, with the increasing curvature of the inner walls of the pipe corners in four flow channels. Compared with the structural optimization at the pipe corners, increasing the curvature of the inner wall of the control shaft and the shell corners reduces pressure loss continuously. Moreover, this study obtains an optimal structure with minimum pressure loss using coupled structure optimization at the control shaft and shell corners.

The scroll-type compressor is the core component of the refrigeration system using the natural refrigerant carbon dioxide. An accurate scroll geometric theoretical model is essential for evaluating and enhancing compressor performance. The present paper proposed and validated an improved geometric theoretical model of a scroll compressor. A vector triangle method-based general piecewise function describes precisely the volume variation of the working chambers, based on which the transient throughflow modeling and performance evaluation of a carbon dioxide scroll compressor were conducted. The mechanisms and influencing factors of the suction precompression and the asymmetry discharging were analyzed. The results indicate that the strength of the suction precompression is mainly influenced by the suction vacuum under different rotating speeds, partly associated with the tangential leakage under low rotating speeds. The increasing initial suction pressure contributes to the linear raising of the pressure difference between suction initial and ending pressures, decreasing the precompression extension slightly. The variation of the discharge throughflow areas of two symmetric discharge chambers dominates the pressure asymmetry, which is gradually eliminated by the overlapping throughflow area. Compared with the circular discharge structure, the waist-shape port reduces the pressure asymmetry degree and shortens its duration.