Influence of Flow Layout on Performance of External Heat Exchanger of Heat Pumps in Electric Vehicles

Abstract:

Based on the uneven distribution of refrigerant flow， a thermal-hydraulic simulation mode for the external heat exchanger of heat pumps in electric vehicles was built， and it is found that the overall performance of the layout of single-pass as well as 4-pass is in an inferior position. Compared with that of the 2-pass configuration， the heat transfer capacity of the single-pass configuration is decreases by 25.3% in summer and 23.3% in winter wet conditions， respectively. The difference between the heat transfer capacities of the configurations of 4-pass， 3-pass， and 2-pass is insignificant. The refrigerant side pressure drops of the structures of 4-pass and 3-pass are 2.5~2.8 and 1.8~2.5 times those of the structure of 2-pass， respectively. The experimental results of the system show that， under various operating conditions， the coefficient of performance （COP） of the heat pump system with the 2-pass external heat exchanger is higher than that of the heat pump system with the 3-pass external heat exchanger. Under wet operating conditions in winter， the heating capacity and COP of the system with the 2-pass external heat exchanger are increased by 6.4% and 9.4%， respectively， compared to those of the system with the 3-pass external heat exchanger. It is concluded that the 2-pass structure is more suitable for the external heat exchanger of heat pumps in electric vehicles.

Key words:electric vehicle heat pump;parallel flow heat exchanger outside the vehicle;flow layout;heat transfer capacity;refrigerant side pressure drop