A novel comparative analysis of heat transfer in a PCM-based heatsink integrated with metal foam under rectangular and trapezoidal pulsed heat fluxes

This work provides an in-depth numerical investigation of how phase change material (PCM) thermally behaves in a PCM-metal-foam heat sink when exposed to time-varying rectangular and trapezoidal pulsed heat fluxes. The PCM undergoes repeated melting and solidifying as the exterior wall is cooled by convective heat transfer. The enthalpy-porosity approach is used to simulate the phase transition, while natural convection effects are treated through the Darcy-Brinkman model. The non-dimensional equations were treated using a finite element discretization and solved in COMSOL Multiphysics. The numerical scheme and resulting outputs were validated through detailed comparisons with available benchmark results, each confirming high accuracy. It was observed that the completion of the first rectangular-pulse cycle corresponds to a 3 K increase in the battery surface temperature relative to its baseline state. At the onset of the second cycle, the PCM has returned to its initial thermal state within that same time frame. Based on these observations, it was found that the total cycle time is approximately 4.5 times longer than the pulse time itself, and the cycles that followed exhibited consistent behavior. In addition, the heatsink behavior was evaluated under a hypothetical scenario in which the thermal pulse followed a trapezoidal shape, while maintaining the same total heat input as the equivalent rectangular pulse. The results showed that when a trapezoidal pulse is applied, the onset of heat-related effects is delayed, the battery surface temperature decreases at each instant, and the period during which the temperature remains at its peak is significantly shorter. In addition, by lowering the maximum and raising the minimum efficiency, the trapezoidal flux limited efficiency fluctuations and yielded a more stable thermal response. Comparison of trapezoidal heat pulses with different decline slopes showed that reducing the pulse slope shortened the dwell time at the peak temperature, thereby enhancing battery safety and prolonging its lifespan. Furthermore, minimizing efficiency fluctuations contributed to improved performance and stability of the heatsink. Lower Biot numbers increased both the average battery surface temperature during the pre-stabilization phase and the dwell time at the peak temperature under rectangular and trapezoidal pulsed heat fluxes.