Revolutionizing electric vehicle cooling: Optimal performance of R1234yf two-phase refrigerant cooling for EV battery thermal management system

This study investigates the effectiveness of R1234yf-based two-phase refrigerant cooling (TRC) in a secondary heat exchanger (test evaporator) designed for battery thermal management systems (BTMS) in electric vehicles. A brazed plate heat exchanger with an offset strip fin configuration is employed to assess various performance metrics, including heat-transfer coefficient (HTC), frictional pressure drop (FPD), cooling performance index (CPI), and inner wall temperature (Tiw). Experiments are conducted across saturation temperatures (Tsat) ranging from 16 to 24 degrees C, mass flux values of 30 to 70 kg/m2s, and inlet vapor-quality levels from 0.1 to 0.8 for standard discharge rates (C-rates) of 1.25. Additional experiments at lower (30 kg/m2s) and higher mass flux (50 kg/m2s) are performed for discharge rates of 1-1.5C to identify optimal conditions. Results indicate that R1234yf exhibits superior cooling performance across all C-rates at 30 kg/m2s and 20 degrees C, with HTC increasing by 28 % for 1C and 26 % for 1.5C. The FPD decreases by 30.5 %, 26.4 %, and 21.9 %, leading to increases in the cooling performance index of 44 %, 33 %, and 24 % for 1C, 1.25C, and 1.5C, respectively. Lower mass flux (30 kg/m2s) yields reduced T iw at T sat of 20 degrees C across all discharge rates, with minimal T iw variations observed within specific xm ranges (0.57-0.67). A novel correlation is developed integrating a proposed battery and heat-transfer model, validated against experimental results with a 25 % error margin, suggesting further exploration in TRC-based BTMS. Additionally, carbon footprint analysis demonstrates the environmental superiority of R1234yf refrigerant, exhibiting a substantial Total Equivalent Warming Impact reduction of up to 4-28 % compared to conventional R134a refrigerant, affirming its eco-friendly nature and potential for utilization in TRC for battery cooling in BTMS.