Nature-inspired triply periodic minimal surface-based structures in sheet and solid configurations for performance enhancement of a low-thermal-conductivity phase-change material for latent-heat thermal-energy-storage applications

Low-thermal-conductivity phase-change materials (PCMs) are often hybridized with high-thermal-conductivity metal matrices to achieve improved heat-transfer performance in latent-heat thermal-energy-storage (LHTES) applications. Owing to recent developments in additive-manufacturing technology that allow any complicated topology to be manufactured with ease, triply periodic minimal surfaces (TPMS) have gained considerable attention. These nature-inspired TPMS structures have already shown promising results in a variety of applications. TPMS structures can be developed in either sheet or solid configurations, both of which exhibit distinct architectures. Herein, a numerical study is presented whereby an organic PCM (docosane) is hybridized with two TPMS structures, namely, gyroids and I-graph-and-wrapped-packages (IWPs) in both sheet and solid configurations. The effective thermal conductivity of each resulting TPMS-PCM composite was calculated using steady-state simulations. Moreover, transient simulations were conducted under isothermal and isoflux conditions to assess the structures' heat-transfer performance. The obtained results were compared with those obtained using PCM only, and the incorporation of gyroid and IWP structures in both sheet and solid configurations was found to significantly improve the PCM's heat-transfer performance. For isothermal case under pure conduction, sheet-based configurations outperformed the solid-based ones with IWP sheet configuration being the best configuration with a PCM melting time of 118 s. However, upon taking buoyancy into account, IWP solid showed best performance with a PCM melting time of 108 s. Furthermore, the performance of each TPMS-PCM composite was found to depend on the type of structure incorporated into it and the value of the applied boundary condition. For isoflux case, IWP sheet showed the best performance in terms of temperature homogeneity in PCM domain as compared to the rest of the TPMS structures under both pure conduction case and the case with buoyancy effects. The PCM melting time in isoflux case was not found to have a strong dependence on TPMS structure type. In both isothermal and isoflux cases, Gyroid solid based TPMS-PCM composite showed the least performance. Moreover, the effects of PCM buoyancy are more pronounced in solid configurations than the sheet ones. Therefore, this study may serve as a design guideline to select appropriate TPMS configuration based on the applied boundary conditions/application.