Thermal Performance of a Layered Bi‐PCM Heat Sink With Nano‐Reinforcement for Passive Cooling of Power Electronics

ABSTRACT Effective thermal management of power electronics is essential to ensure operational reliability as device power densities increase. This study numerically investigates the thermal performance of a newly proposed layered biphasic phase‑change material (Bi‐PCM) heat sink enhanced with copper nanoparticle reinforcement for passive cooling applications. A two‐stage optimization approach is employed, combining architectural design (PCM sequencing and volumetric distribution) with nano‐reinforcement strategies, using validated transient computational fluid dynamics simulations based on the enthalpy–porosity method. Among the 10 configurations tested, results show that the Regressive Gradient Strategy, where the high‐melting‐point PCM (RT55) is positioned adjacent to the heat source, provides superior performance. The optimal configuration (70% RT55–30% RT42) achieves an operational time of 72.04 min, representing a 3.69% improvement compared with the best Progressive Gradient Strategy configuration. This enhancement is attributed to delayed melting onset and improved latent heat utilization. Nano‑reinforcement with uniformly dispersed copper nanoparticles (3 vol% in both layers) further improves the performance of the optimal Bi‑PCM architecture, increasing the operational time by 2.16% (to 73.60 min) and lowering the peak temperature by 5.5% (to 73.34°C) relative to the nonreinforced reference. The results demonstrate that architectural optimization (PCM sequencing and volumetric distribution) plays a dominant role in thermal regulation, while nano‑reinforcement provides a secondary but significant enhancement. The proposed configuration and optimization framework offer physics‑based design guidelines for advanced passive thermal management of power electronics and can be readily extended to multi‑PCM systems.