Thermal performance and behavior of phase change material under consecutive thermal shocks in hybrid battery thermal management system

Battery thermal management systems (BTMSs) that couple phase change materials (PCMs) with liquid-cooling are increasingly deployed in electric vehicles operating under dynamic, high-power duty cycles. However, the thermal response of PCM under consecutive thermal shocks, where residual heat from one shock carries into the next, has not been systematically characterized. This study investigates the thermal-history dependence of PCM in a hybrid PCM–liquid-cooling BTMS through experimentally validated numerical simulations across twelve cases that vary shock power level (2C and 4C), number of shocks, interval duration, and shock duration. A critical liquid fraction (LF) threshold of approximately 40% is identified at the onset of the second shock. Below this threshold, the second-shock temperature rise remains within 12 °C, whereas above it the rise escalates to 27–32 °C under high heat loads as the solid buffering layer near the heat source is thins and channelization of the molten zone develops. Three convective regimes (weak recirculation skeleton, strong convection activation, and recovery decay) characterize this transition. Extending the interval between shocks does not necessarily mitigate the peak response once the liquid fraction exceeds the threshold, because latent heat capacity continues to be consumed under background heat generation that persists throughout the interval. These findings provide a risk-based framework for BTMS operation, in which the liquid fraction at the onset of a thermal event serves as a safety indicator to guide cooling intervention according to the anticipated heat load intensity.