Numerical and experimental investigation on electric vehicles battery thermal management under New European Driving Cycle

Studies have confirmed that using phase change materials (PCM) as a battery thermal management system (BTMS) in the battery pack controls the battery's temperature and improves its performance; however, it undeniably imposes a significant weight on EV. Therefore, a pivotal issue remains, the best economic battery pack design and required PCM to guarantee the pack's performance. This paper optimizes the arrangement of the hybrid PCM-Air BTMS by the multi-objective Response Surface Method (RSM) to enhance the system's cooling achievement under the New European Driving Cycle (NEDC). The influence of four factors, including; 1) PCM thickness (A), 2) air gap (B), 3) air velocity (C), and 4) PCM type (D), are investigated. The objective of the optimization is to minimize the highest and mean battery temperature and the temperature difference among cells, as well as maximize the total liquid fraction and the power density per cost ((W/m3)/$) (PDC). polyethylene glycol-1000 (PEG-1000) is applicable for high-speed inlet air and short distances (up to 2hr driving time), and PEG (1500) for low-velocity inlet air and longer distances. Increasing the C does not always reduce the cell temperature. Also, C up to 1 m/s cannot reliably keep the cell temperature in a safe range. Increasing A at low Cs improves cell temperature and at higher Cs warms the cell. Increasing A, B, and C can significantly control the temperature difference. One of the best optimal conditions is: A = 1.7, B = 2.37, C = 0.93, D = PEG(1000). This pack is almost 91% cheaper than conventional BTMSs in today's EVs; In fact, by investing 1$ per each unit volume (1m3) in a similar EV, almost 20% more cells (power) can be mounted in this pack. Finally, this pack was fabricated under optimum point specifications, and experimental results were well consistent with the simulation results.