Topology optimization for accelerating thermal charging in TPMS-based latent heat storage units: A rapid method for determining porosity distribution

The thermal charging performance of latent heat thermal energy storage (LHTES) devices using phase change materials (PCMs) is severely limited by their low thermal conductivity. Embedding triply periodic minimal surface (TPMS) structures has emerged as an effective strategy to enhance heat transfer. However, existing TPMS porosity designs largely rely on heuristically prescribed gradients, typically derived through trial-and-error approaches, which limits both their efficiency and generality. In this study, a topology optimization framework was developed to rapidly and systematically identify high performance spatial porosity distributions for TPMS-PCM composites. The framework innovatively coupled a transient phase change heat transfer model with a density-based topology optimization loop, in which the design variable explicitly represented the local TPMS porosity, ensuring that intermediate design values remain physically interpretable and directly manufacturable. The topology optimization results revealed a positive porosity gradient in the main region of the TPMS, while slight negative gradients emerged near the heat source and at the far end. The optimized porosity distribution (TO-TPMS) was converted into a manufacturable TPMS geometry, fabricated via selective laser melting, and validated through combined experimental and numerical investigations. Results demonstrate that TO-TPMS consistently achieved higher temperatures, faster melting rate, and superior heat storage performance compared with uniform and linearly graded TPMS structures, with a 14.7% reduction in melting time and a 4.1% increase in total accumulated heat. These findings confirm that topology optimization provides an efficient and reliable pathway for designing high performance TPMS-based LHTES systems.