Numerical analysis in a full-scale thermal energy storage tank with dual PCM capsules

Sensible thermal energy storage has been widely used with a single water storage tank for both heat-mode and cooling-mode. However, a large water storage tank is required to avoid the inevitable limitation of low energy storage density. Although latent heat thermal energy storage has compatibly high energy storage density, it requires separate tanks for heating-mode and for cooling-mode. This study considered a single tank for both heating and cooling modes, composed of 1620 (9 × 9 × 20) capsules filled with cooling-PCM or heating-PCM. Recently our research group developed a new effective thermal conductivity model that properly reflected the increased strength of natural convection in the molten PCM, and in this study we applied the model to simulate the full scale tank. Five different mixing ratios of cooling-PCM and heating-PCM, defined as the capsule number filled with cooling-PCM or heating-PCM to the total capsules in the tank, were investigated, and the range of the ratio of cooling-PCM and heating-PCM was found to satisfy both the required energy storage densities in heating and cooling demand. For the required energy storage densities of heating mode, 25 kwh/m³, and cooling mode, 30 kwh/m³, the results suggest the combined ratio in the dual PCM tank is within a 50/50–90/10 mixing zone ratio, of the cooling-PCM/heating-PCM respectively.