Evaluation and comparison of thermal performance of latent heat storage units with shell-and-tube, rectangular, and cylindrical configurations

Latent heat storage plays a significant role in tackling the mismatch between energy supply and demand. Evaluation and comparison of the thermal performance of different shaped latent heat storage units (LHSU) are essential in the optimal design of LHSU. This study developed the numerical model of heat transfer and flow in shell-and-tube, rectangular, and cylindrical LHSU with the same PCM mass and heat transfer area. Two kinds of criteria, namely the j/f factor considering both heat transfer and flow resistance and the exergy coefficient evaluating irreversibility, are proposed to assess the performance of LHSU comprehensively. It shows that natural convection intensity in cylindrical LHSU is the highest, while the shell-and-tube LHSU exhibits the lowest phase change time and the highest heat transfer rate. The average j/f factor of shell-and-tube LHSU is 21.4% larger than that of rectangular LHSU and is twice as much as that of cylindrical LHSU. Therefore, the shell-and-tube LSHU achieves the best overall thermal performance. Moreover, cylindrical LHSU achieves the highest melting exergy efficiency of 81.5%, while shell-and-tube LHSU has the highest solidification exergy efficiency of 62.8%. Regarding the thermal storage and release cycle, the exergy efficiencies of shell-and-tube, rectangular, and cylindrical LHSU are 50.1%, 49.2%, and 48.5%, respectively. Therefore, shell-and-tube is the optimal shape to achieve the largest exergy efficiency of the thermal storage-release cycle. This study deepens the understanding of the thermal behavior of PCM packed in different shaped containers, obtains the optimal geometric configuration, and gives guidance to the optimal design of geometric parameters of the LHSU.