Evaluation and optimization of thermal performance for a finned double tube latent heat thermal energy storage

•Melting performances for a horizontal LHTES unit with different fins arrangements are evaluated.•The relation between fins arrangement and complete melting time of PCM under different parameters are revealed.•An optimum fins arrangement is recommended to accelerate melting. Embedded fin in phase change materials (PCMs) is one of the most efficient methods to enhance the heat transfer between the PCM and heat transfer fluid (HTF). An appropriate arrangement of the fins plays significant role to design a highly efficient latent heat thermal energy storage (LHTES) unit. The aim of this study is to find the most efficient arrangement of fins to accelerate the charging rate. A two-dimensional numerical model based on finite volume method (FVM) was developed with considering natural convection and the calculation results were validated with experimental data. The heat transfer characteristics of LHTES unit with different fins arrangements were firstly explored. These include no fins, straight fins, angled fins, lower fins and upper fins. Then, the effects of fins number (N), dimensionless fins length (l), heat transfer fluid temperature (Tw) and outer tube material on melting performance for four arrangements were studied. In addition, the best type of arrangements to increase the efficiency of heat exchanger was suggested. The performance enhancement of LHTES through fins configuration were quantitatively described based on complete melting time and heat storage capacity, and the conclusions are arrived as follows: when N ≤ 6, the optimum arrangement is the lower fins, while it is the angled fins when N > 6. For N = 6, only l could change the optimum arrangement of fins. At l equals 0.5 and 0.95, the optimum arrangement is angled case. While at l = 0.75, the optimum arrangement is lower case. It is also found that the heat storage capacity of lower fins configuration is minimal compared to other three configurations.