Synergistic enhancement of PCM melting in inclined latent heat thermal energy storage units via fin integration

The substantial waste heat generated during ship operation provides considerable potential for energy recovery. Latent heat thermal energy storage (LHTES) using phase change materials (PCMs) is a promising solution. However, its application is constrained by low thermal conductivity of PCMs. In this study, a three-dimensional (3D) transient numerical model is developed to investigate melting behavior of paraffin in a shell-and-tube LHTES unit, with systematic emphasis on the coupled effects of fin length, fin number, and inclination angle (0°, 45°, and 90°). The results indicate that the 45° inclined orientation consistently outperforms both horizontal (0°) and vertical (90°) counterparts, as it promotes a 3D flow that intensifies natural convection in molten PCM. In addition, increasing the fin length strengthens conductive heat transfer and sustains efficient heat transfer throughout phase change process. Among the cases studied, the configuration with eight fins of 20 mm length at 45° shortens the melting time by 20.4% relative to the horizontal configuration with the same fin arrangement, and by 74.8% relative to finless horizontal baseline. These findings reveal the coupled roles of fin geometry and orientation in governing phase change heat transfer and offer design guidelines for inclined LHTES systems in ship waste heat recovery applications.