Numerical study on the thermal enhancement of horizontal latent heat storage units with hierarchical fins

Abstract The poor thermal performance of shell and tube latent heat storage (LHS) units using phase change materials restricts large-scale renewable energy utilisation. To address this issue, an innovative hierarchical fin is designed here to improve the charging performance of horizontal LHS units. The charging characteristics of innovative LHS units are explored and compared with available LHS units by a numerical model using the enthalpy-porosity scheme. Moreover, the response surface method (RSM) is applied to optimise the hierarchical fin by maximising its charging rate. The results indicate that hierarchical fins significantly improve the charging rate and temperature uniformity of horizontal LHS units. Except for the early heat conduction stage, melting convection develops as the dominant mode in the middle stage but decays in the later stage. Compared to tree-shaped fins, the hierarchical fin dramatically enhances heat conduction performance in the late melting stage, leading to a maximum reduction of 41.1% in the whole melting time of horizontal LHS units. To maximise the charging performance, the RSM results suggest the thickness gradient of the primary bifurcation, thickness fractal dimension, and length ratio of hierarchical fins should be 3.98, 1.34, and 1.11, respectively, providing constructive guidance for engineering applications of horizontal LHS units.