Analyses of the thermal and hydraulic characteristics of a perpendicular-flow offset-strip-fin heat exchanger for electric vehicles

The heat pump in an electric vehicle (EV) helps to mitigate thermal issues of reduced mileage under cold climate conditions, and improving the performance of heat exchangers can further enhance efficiency. However, the thermal-hydraulic characteristics and performances of such heat exchangers in summer conditions have been often overlooked. In this study, an advanced heat exchanger with a new structure using perpendicular-flow offset-strip fins is proposed, and the condensation performance of R-1234yf is analyzed under various actual operating conditions. The effect of the flow direction of the offset-strip-fin is examined by conducting a comparative experiment. The perpendicular-flow offset-strip-fin heat exchanger (OSFHX) has a 69 % higher heat transfer rate than the plate heat exchanger, but with a higher pressure drop. The heat transfer coefficient correlations for the coolant and single-phase refrigerant are newly developed. Also, the condensation performance of the OSFHX within the range of actual operating conditions is analyzed by using the discretization method. The results show that the perpendicular-flow OSFHX had a 49 % higher condensation heat transfer rate than the chevron-type heat exchanger. The combined structure of two heat exchangers improves the heat transfer rate by 16 % compared to a typical single heat exchanger. This unique structure can improve heat transfer performance by increasing the temperature difference between the two-phase refrigerant and the coolant in summer operating conditions.