Comprehensive investigation of a novel latent energy storage unit exhibiting enhanced natural convection

This study proposes a heptahedron energy storage enclosure designed to enhance natural convection. It is characterized by an increased volume near the top, reduced volume near the bottom, and minimized volume at the corner of the right wall. The effects of the length ratio (LT/LB) of top and bottom surfaces and the length (LR) of the vertical wall opposite the hot wall on the melting characteristics of RT42 phase change material (PCM) in the heptahedron energy storage unit are explored by three-dimensional numerical simulation. The results indicate that the heptahedron structure prolongs the dominant melting stage involving convective heat transfer, enhances natural convection, and mitigates the impact of PCM at the corners in the final melting stage. Specifically, when LR=2 mm and LT/LB=1.71, the heptahedron exhibits the highest convection intensity, the maximum melting rate and mean power of the PCM. Additionally, the temperature distribution in the heptahedron is the most uniform under the same conditions. Compared to the rectangle structure, the optimal heptahedron enclosure reduces melting time by 9.3% and increases mean power by 8.47% at the same wall temperature of 57 degrees C. After 25 min of heating, the average temperature of the PCM rises by 1 degrees C.