Experimental and numerical analysis of thermal charging and discharging in an additively manufactured TPMS-based latent heat storage device

Triply periodic minimal surface (TPMS) structures provide a large heat-transfer area and interconnected flow passages, but their behavior in LHS devices with coupled convection and phase change remains poorly characterized. In this work, an additively manufactured Primitive TPMS LHS device was fabricated and tested during charging and discharging, and a numerical model was used to investigate the phase-change process and evaluate structural parameters. The experimental results show that natural convection in the molten PCM produces inter-cell circulation and vertical thermal stratification. Under the standard charging condition, the layer-averaged PCM temperature difference between the upper and lower layers reached 14.2 °C. The latent heat remains the dominant contribution, accounting for 60.7–70.5% of the stored heat during charging and 64.0–71.8% of the released heat during discharging, while sensible heat in the PCM and TPMS skeleton cannot be neglected. Increasing the HTF inlet temperature mainly enhances the charging/discharging rate by increasing the thermal driving force, whereas increasing the HTF flow rate from 200 to 1100 L/h shortens the complete melting and solidification times by 37.5% and 19.9%, with only minor changes in the total stored/released heat. Numerical analysis shows that increasing the PCM-to-HTF volume ratio from 0.5 to 2.5 raises the heat storage density from 85.1 to 185.2 MJ/m³, but reduces the energy storage-to-pumping work ratio (EPR) from 5.18 to 0.04. Reducing the cell size from 20 to 2 mm shortens the melting time from 167.0 to 5.0 s and increases EPR from 1.81 to 5.31. These results indicate that TPMS-based LHS design should balance PCM inventory, charging rate, and pumping work rather than maximizing storage volume alone.