Numerical investigation of phase change material-integrated triply periodic minimal surface heat exchangers for thermal energy storage

Additive manufacturing has enabled the fabrication of heat exchangers with geometrical complexity not achievable through conventional methods. Triply periodic minimal surfaces (TPMS), particularly gyroid, diamond, split-P, and lidinoid structures, offer high surface area and favorable fluid mixing characteristics that make them promising candidates for heat exchangers with integrated thermal energy storage. This study investigates the thermal charging behavior of TPMS-based heat exchangers that incorporate a phase change material (PCM). A transient numerical model was developed in ANSYS Fluent 2025R2 and validated against experimental measurements. The validation focused on matching the transient inlet temperature profile, flow conditions, and melt behavior reported in the experiment. Once validated, the model was used to compare the performance of gyroid, diamond, split-P, and lidinoid TPMS geometries and to evaluate the influence of operating conditions. Baseline simulations were conducted at an inlet temperature of 30 °C and a flow rate of 250 mL/min. Additional studies examined inlet temperatures of 30, 35, 40, and 50 °C and flow rates of 250, 300, 350, and 500 mL/min. The results provide a comparative assessment of PCM-integrated TPMS heat exchangers under consistent thermal storage capacity and operating conditions, highlighting how topology and its associated geometric characteristics govern the trade-off between accelerated PCM melting and increased hydraulic resistance across the gyroid, diamond, split-P, and lidinoid geometries.