A leaf-vein-inspired design of three-order hierarchical metal foam for heat transfer enhancement of phase change materials

Integrating metal foam into phase change materials (PCMs) effectively overcomes their inherent low thermal conductivity, significantly enhancing energy conversion efficiency. However, such improvement strongly depends on the foam's microstructure. Inspired by leaf venation networks, this study proposes a novel three-order foam design composed of a vertical primary vein, inclined secondary veins, and a tertiary vein network between secondary veins, establishing efficient heat transfer channels within PCM composites. Through experimental and numerical analyses, both symmetric and asymmetric configurations are investigated to examine the influences of the branch angle of secondary veins and the presence of tertiary vein network on melting dynamics. The results reveal that heat transfer during the melting process is primarily dominated by thermal conduction, while natural convection plays a negligible role. Moreover, increasing the branch angle significantly improves melting performance, leading to shorter complete melting time and higher energy storage rate and efficiency. More importantly, the introduction of the tertiary vein network further enhances heat transfer performance. Specifically, at a branch angle of 60°, the complete melting time is reduced by 46.04 % compared with the two-order structure without tertiary veins, while the energy storage rate increases by approximately 4 times and the energy storage efficiency improves by 85.32%. These findings offer valuable bioinspired design principles and optimization strategies for engineering advanced PCM composites in thermal energy applications.