Evaporation performance of propane in offset strip-fin plate heat exchanger for refrigerant-based battery thermal management in electric vehicles

Abstract

This study investigates the potential of refrigerant-based cooling (RC) using a natural refrigerant (propane) and lightweight energy-efficient brazed plate heat exchangers (PHXs) in the battery thermal management systems (BTMSs) of the electric vehicles (EVs). Experimental assessments were conducted to analyze the evaporative heat transfer characteristics of propane within an offset strip-fin flow-structured PHX under various operational conditions resembling the BTMS operation. The battery discharge rates, often represented by the C-rate, are determined by the discharging current relative to the battery's capacity. In this study, a heat generation model based on the C-rate was employed to evaluate the thermal performance of the battery. Parameters, such as mass flux (G) at 30–70 kg/m2s, discharge rates (C-rate) of 1, 1.25, and 1.5C, and saturation temperatures (Tsat) of 16–24 °C were explored, with the inlet vapor quality (xin) in the range of 0.1–0.8. The influence of G and Tsat on the heat transfer performance showed that higher G values (60 and 70 kg/m2s) achieved the maximum heat transfer coefficients (HTC), which resulted in impractical pressure drops (PD). While higher HTC and lower PD were observed at a Tsat of 24 °C, concerns about increased inner wall temperature (Tiw) and safety emerged at this temperature. Hence, the optimum conditions of G (30 and 50 kg/m2s) and Tsat (16 and 20 °C) were investigated. The average HTC increased by 29, 27, and 21 % at 50 kg/m2s compared to that at 30 kg/m2s with Tsat of 20 °C, resulting in an average of 0.7, 0.9, and 1.2 °C reduction in the Tiw for C-rates of 1.5, 1.25, and 1C respectively. Compared to the Tsat of 16 °C, higher HTC and lower PD were observed at 20 °C, however, the Tiw was in the range of 21.12–20.47 °C for Tsat of 20 °C, which is 3.5–4 °C higher than that at Tsat of 16 °C. The results from the critical heat transfer coefficient analysis showed that the peak heat dissipation with minimal wall temperature was attained with optimal xm of 0.45–0.5, which enhanced the cooling efficiency for both the G values of 30 and 50 kg/m2s, and both the Tsat values (16 and 20 °C).