Enhancing Molten Salt Melting in Tube Heat Exchanger through Segmented Fin Design for Thermal Energy Storage

Abstract

Latent heat thermal energy storage (LHTES) systems using phase change materials (PCMs) provide high energy density, but the low thermal conductivity of PCMs limits heat transfer and extends the melting time. A three-dimensional enthalpy-porosity numerical model is developed for a double-tube molten salt storage unit, where 520 K hot water flows through the inner tube and the outer tube is adiabatic. A segmented fin structure is proposed to balance PCM volume, conductive heat transfer pathways, and natural convection flow space. The effects of fin spacing ratio, rotation angle, and aspect ratio on liquid fraction evolution, melting time, temperature distribution, flow velocity, and stored energy are investigated. The preferred fin parameters (spacing ratio of 0.8, rotation angle of 60°, and aspect ratio of 1.25) reduce the complete melting time by 1.56%, 2.78%, and 10.03%, respectively, compared with the initial segmented fin case. Compared with the continuous fin configuration, the segmented fin configuration increases the final heat storage by 2.16 kJ due to the increased PCM volume. The results indicate that the performance of segmented fins depends on the combined effects of multiple geometric parameters rather than individual parameter variations. The selected segmented fin design provides a practical strategy for balancing thermal storage capacity and melting performance in PCM based LHTES units with internal heat transfer fluid.