Investigating the performance optimization of an outdoor condenser–evaporator for an electric vehicle heat pump system

Abstract

To analyze the dual-use characteristics of outdoor microchannel heat exchangers in electric vehicle heat pump systems, numerical calculation models of the heat transfer and pressure drop under different states were analyzed and selected. The heat transfer and flow characteristics of the heat exchanger were simulated and experimentally studied. Additionally, the heat transfer and flow performance of the heat exchanger under different wind velocities and process conditions were discussed, and the temperature uniformity on the surface was analyzed. The simulation results show that the calculated value and the experimental error of the heat exchanger performance are within 9%–15%. Regarding the refrigerant side, the number of internal holes in the flat tube and the aspect ratio of the internal holes should be appropriately selected according to the heat transfer effect and pressure drop based on the simulation. In addition, regarding the air side, the proper fin spacing and opening angle can improve the comprehensive performance. The experimental results for the heat pump system show that the comprehensive performance of a two-pass heat exchanger is better than a three-pass heat exchanger. Under low-temperature heating conditions, the temperature uniformity coefficient of the two-pass heat exchanger is 12% lower than that of the three-pass heat exchanger; thus, the two-pass heat exchanger exhibits a better heat exchange effect. It was found through experiments that a proper increase in the compressor speed can reduce the temperature uniformity coefficient when the outdoor heat exchanger is employed as an evaporator, thus making the refrigerant distribution more uniform.

Keywords

• Electric vehicle
• Microchannel heat exchanger
• Heat pump
• Temperature uniformity