Effect of natural convection on charging of phase change materials in graded metal foam: Pore-scale simulation

Open-cell metal foams (MFs) possess exceptional thermal conductivity and are often utilized to enhance the phase transition efficiency of phase change materials (PCMs) that have insufficient thermal conductivity. The movement of energy within MFs during phase transition is influenced by natural convection and heat conduction. In this study, pore-scale numerical simulation (PNS) was employed to study the effect of natural convection on the phase transition of graded MFs (positive gradient foam-PGF, homogenous foam-HF, and negative gradient foam-NGF). Simplified tetrakaidecahedron cells were used for PNS to capture the primary geometric features of MFs. Results have shown that natural convection significantly influences the phase transition process of PCMs. Compared to pure thermal conductivity, the full melting times (FMTs) of PCMs in PGF, HF, and NGF were reduced by 85.2% - 88.3% when natural convection was considered. Furthermore, the integrated average temperature response rates of PCMs in PGF, HF, and NGF, considering natural convection, were improved by 378.4%, 301.9%, and 342.5%, respectively. The presence of natural convection resulted in a gradient in the phase interface distribution and temperature field. The PNS method proved useful in illustrating the influence of metallic ligaments on phase interface and temperature distributions.