Evaluation and regulation of solid–liquid phase change process based on thermal resistance analysis in fluid domain

Phase change materials (PCMs) exhibit excellent thermal stability, cycling performance, and high energy storage density, and are widely applied in thermal energy storage systems. However, the simple structure of conventional storage units leads to a single heat flow path, resulting in low heat storage efficiency and severely restricting effective energy utilization. Due to limitations in experimental methods during the phase change process, current optimization approaches mainly rely on global analyses of temperature fields, flow fields, solid–liquid interfaces, and global parameters such as liquid fraction and melting time, while lacking detailed local analysis and evaluation, making it difficult to reveal the mechanisms behind thermal performance improvement. In this study, by altering the boundary conditions and aspect ratios of the storage unit, the local and global flow and heat transfer behaviors were analyzed based on the thermal resistance analysis methodology. It was found that distinct “tree-shaped” high thermal resistance zones appear inside heat storage units, and when the aspect ratio is 16:4, multiple “tree-shaped” zones emerge. Accordingly, a “tree-shaped” fin arrangement within these regions and the thermal resistance evaluation factors were proposed. With the addition of fins, the average evaluation factors F_x and F_y decreased by 68.11 % and 60.29 %, respectively. Compared to conventional straight fins, the “tree-shaped” fin structure further reduced F_x and F_y by 23.96 % and 28.34 %, respectively, and significantly improved the total stored heat rate. This study provides simple insights into the design and optimization of high-efficiency thermal storage systems.