Melting and solidification characteristics of integrated phase change material/triply periodic minimal surface structures: Toward augmented latent heat thermal energy storage systems

Triply periodic minimal surfaces (TPMS) enhance the low thermal conductivity of phase change materials (PCMs) in latent heat storage systems, providing better thermal performance than traditional metal foams due to their superior surface area and interconnected pore networks. However, researchers have not systematically studied the charging and discharging performance of PCM with different TPMS structures under varying heat source temperatures and orientations. In this study, a transient 3D CFD model was developed to assess the phase change of paraffin wax within four TPMSs (Gyroid, IWP, Primitive, and Neovius). The investigation proceeded in two stages: first, examining the effect of four heating temperatures (333 to 363 K) under bottom heating, and second, analyzing the influence of three heating orientations (bottom, top, and side) at the temperature extremes (363 K melting, 293 K solidification). The results show that lattice geometry and surface temperature are the primary determinants of phase change dynamics. The Gyroid and IWP lattices exhibit superior thermal performance, achieving rapid PCM melting and solidification. Specifically, at 363 K, the PCM in both structures melted in approximately 180 s, and increasing the temperature from 333 K to 363 K reduced the PCM melting time in the Primitive structure by 46.5%. During solidification, the PCM in Gyroid and IWP structures solidified 100 to 150 s faster than Primitive/Neovius, with the discharge time being insensitive to the surface temperature. Notably, under side heating, the Primitive structure shows higher energy retention during discharge (19% SOD vs. 9% for Gyroid at 600 s), despite the Gyroid having a higher initial state of charge (50% SOC at 100 s).