Experimental characterization of a triply periodic minimal surface PCM-to-air thermal energy storage device

The expansion of energy production has intensified research into thermal energy storage (TES) to manage variability and improve system efficiency. Heat exchanger design is critical to achieving high power densities in TES systems. This study presents a high-surface-area phase change material (PCM)-to-air heat exchanger fabricated via resin-based stereolithography with a novel gyroid-based geometry tailored for enhanced performance. Material properties of the commercial PCM and resin were characterized using analytical techniques. A controlled air loop was used to evaluate heat transfer and pressure drop at various flow rates and inlet temperatures. Results show a strong dependence on the inlet temperature difference ($\Delta T$) relative to the PCM melting point. During charging at the highest flow rate, increasing the inlet air temperature from $\Delta T=5°$C to $20°$C above the melting point increased the average heat transfer rate by 187%. During discharging, decreasing the inlet temperature by the same $\Delta T$ below the melting point led to a 232% increase. Notably, the high-surface-area design enabled nearly symmetric charging and discharging behavior, a novel result for PCM-based TES systems which are often restricted by natural convection and other effects. The overall heat transfer coefficient was calculated and compared to values from standard design correlations. The maximum thermal effectiveness reached 95% at $\Delta T=20°$C and a moderate flow rate of 34 m${}^3$/h. Peak coefficients of performance (COP) of 7 during charging and 6.4 during discharging were observed at $\Delta T=20°$C and a low flow rate of 20 m${}^3$/h. These results demonstrate the viability of additively manufactured geometries for advanced TES applications.