Numerical Simulation and Analysis of Heat Transfer Characteristics in Gradient‐Porosity Foam Copper Composite Phase Change Materials

Phase change materials (PCMs) exhibit significant potential in energy storage and thermal regulation applications, attributed to their high latent heat capacity. However, the low intrinsic thermal conductivity of PCMs requires the incorporation of thermal enhancement materials, such as copper foam, which provides a high specific surface area and excellent thermal conductivity. Nevertheless, the mechanisms underlying the influence of copper foams with varying porosity gradients on the phase transition process of PCMs remain unclear. To address this issue, we employ numerical simulations to investigate the effects of uniform and gradient porosity distributions on the melting behavior of copper foam‐enhanced PCM composites. Three uniform porosity models (0.85, 0.90, 0.95) and three gradient porosity models (including positive gradient: 0.85–0.90–0.95; mixed gradient: 0.85–0.95–0.90; and negative gradient: 0.95–0.90–0.85) were developed, with paraffin serving as the PCM. The results demonstrate that in uniform porosity models, a lower porosity (0.85) leads to the shortest melting time owing to superior thermal conductivity, whereas a higher porosity (0.95) enhances thermal uniformity in later stages by facilitating natural convection. Among gradient porosity structures, the positive gradient design significantly improves heat transfer efficiency via a synergistic mechanism—enhanced thermal conductivity near the heat source combined with improved convection in distal regions—resulting in a 14.9% reduction in melting time compared to the uniform 0.85 porosity model, along with the most uniform temperature distribution. In contrast, the mixed and negative gradient configurations demonstrated inferior performance, with melting times prolonged by 22.7% and 44.2%, respectively, compared to the uniform 0.85 porosity model. This study elucidates the critical role of gradient porosity in optimizing the balance between conduction and convection, offering theoretical insights and design strategies for high‐efficiency thermal energy storage systems.