Heat transfer enhancement of multi-tube latent heat storage unit based on topology optimization

The low thermal conductivity of phase change material (PCM) limits the efficiency of heat transfer in latent heat thermal energy storage systems. Adding topology optimization fins and heat transfer fluid (HTF) pipe rearrangement can achieve performance enhancement, however, current topology optimization methods mainly focus on single-pipe concentric configurations, ignoring the potential advantages of optimizing multi-pipe systems. In this study, we propose a new approach that combines topology optimization with tuning the multi-pipe layout to develop efficient latent heat thermal energy storage systems. We found that the HTF tube layout plays a key role in the evolutionary morphology of the topology optimization fins through numerical studies. The results show that the HTF tube layout affects the growth conformation of topology optimization fins, and the centered arrangement has more trunks and branches compared to the arrangement near the wall for the same fin volume ratio; however, the arrangement on the outer side helps the melting of the bottom-stacked PCMs during the phase transition process, and the arrangement on the outermost side (Case7) results in a complete melting time of 39% compared to that of the innermost side (Case1). The Case3 arrangement is closer to the outside than the Case2 arrangement, but the Case2 centered arrangement has more fins and a more uniform distribution with a shorter complete melting time, which suggests that the optimal HTF tube arrangement is a combination of accelerating the melting of the bottom-stacked PCM as well as facilitating the topology optimization of the fins to grow out of the multi-branch structure. The multi-tube topology optimization structure is able to reduce the complete melting time by 35% and 77% compared to the single-tube topology optimization structure and the conventional fin structure, respectively, and has better heat transfer capability. This paper can provide new ideas for using topology optimization fins to improve the performance of phase change heat storage units.