Modeling three-dimensional flow in a thermal energy tank: Numerical analysis of the impact of tank shape on the melting and solidification of phase change material

Phase-change materials (PCMs) used for heat storage has shown to be extremely promising because of their capacity to both hold and release a lot of energy throughout the phase shift process. However, there is a need to optimize the design and configuration of solar thermal collector systems to improve their efficiency. In this numerical analysis, we investigated the melting and solidification behavior of different phase change material (PCM) cylinders with varying aspect ratios (L/D) in five tanks. We used several thermodynamic performance measures such as contours of the liquid fraction, temperature, and water heat flux to assess the effectiveness of the system. The findings revealed that the duration needed for the PCM to completely melt within each tank ranged from approximately 2670 s in tank 4 to 2880 s in tank 1, while the time for complete solidification ranged from approximately 10,560 s in tank 3 to 11,760 s in tank 5. Moreover, we found that the tank shape has a substantial impact on the heat flux of water during both melting and solidification processes. Specifically, during process of melting, an increase in the aspect ratio (L/D) led to a higher level of thermal stratification and an increased melting rate. This trend was consistent across all tanks, except for tank 5, which we considered a special case in our study. Similarly, an increase in the aspect ratio (L/D) during the solidification process resulted in a faster solidification rate, with tank 3 having the shortest solidification time. However, there are limits to this increase to avoid a reversed result.