Melting performance study and multi-objective optimisation of phase change triplex tube heat exchangers with secondary branching palmate mesh vein fins

Numerical simulations are carried out to investigate the influence of secondary branching palmate mesh vein fins on the melting of phase change materials (PCMs). The combined impact of four structural variables on the complete melting time and the heat transfer rate is evaluated by response surface methodology (RSM), and the predictive correlation equation is derived. The fin structure is optimised using the non-dominated sorting genetic algorithm II (NSGA-II) to obtain the Pareto-optimal solution. The results demonstrate that the Pareto optimal point achieved the shortest melting time of 1600.1s and the maximum heat transfer rate of 959.8W. Building on this foundation, a comparative analysis is conducted across three dimensions: the number of secondary branching layers, the arrangement type, and the fin geometry. This analysis illustrates the superiority of the proposed fin structure. Analysis indicates that melting performance improves with increasing secondary branching layers, with the most pronounced strengthening effect observed when secondary branching occurs at the first layer. Compared to unidirectional arrangements, bidirectional fins facilitate heat transfer from both the inner and outer tubes, resulting in a more uniform heat distribution. Compared to rectangular and tree-shaped fins, the secondary branching palmate vein fins facilitate heat diffusion across a broader PCM area, thereby accelerating PCM melting. In summary, the secondary branching palmate vein fins exhibit an exceptionally uniform temperature distribution within the PCM domain and outstanding melting performance.