Enhancing performance in heat storage unit and packed-bed system: Novel capsule designs inspired by drop structure

Packed-bed system offers a promising solution to the uneven spatiotemporal variability of solar energy. However, challenges persist in its development, including excessive disparity in localized temperature, sluggish heat storage rate, and suboptimal efficiency. In this context, the drop structure phase change material capsule concept was proposed to enhance thermal energy storage performance, drawing inspiration from the streamlined structure such as tuna or submarine. This research delves into the comprehensive performance of drop, sphere, and shuttle structure capsules, encompassing experimental investigation and simulation analysis of the external convection, internal melting, and charging processes. Additionally, an experimental visualization setup was devised to monitor the melting process. The results indicated that replacing conventional sphere structure capsule with the drop structure capsule reduces the drag of external flow by 10.12 %. The complete melting time of the individual capsule and the packed-bed system was shortened by 5.53 % and 10.94 %, respectively. Furthermore, the standard deviations of the longitudinal and radial average temperatures decreased by 24.12 % and 29.97 %, respectively.