Numerical Assessment and Entropy–VIKOR Selection of Fin Materials for a Shell-and-Tube Latent Heat Storage Unit

The integration of latent heat storage with solar thermal systems offers an effective solution to address the intermittency and variability of solar energy availability. Thermal energy can be effectively stored in a shell-and-tube type latent heat storage unit (ST-LHSU). The charging/discharging rate of ST-LHSU is quite low, and therefore, the use of heat transfer enhancement techniques proves quite beneficial. Fins can significantly improve the heat transfer rate of the storage unit. The effect of different fin materials on the solidification performance of an ST-LHSU was investigated in this study. Herringbone wavy fins were considered for the study, and the thermal performance of fins made from aluminum (F-1), copper (F-2), mild steel (F-3), and stainless steel (F-4) was evaluated numerically. Results show that the total solidification time for F-1, F-2, F-3, and F-4 was 7778, 7114, 8579, and 8250 s, respectively. Among the considered materials, F-2 provided the shortest solidification time due to the high thermal conductivity of copper. However, considering only thermal performance may not provide a practical material selection. Therefore, an entropy–VIKOR multi-criteria decision-making method was applied by considering total solidification time, relative fin mass, and estimated raw-material cost as the selection criteria. The obtained overall ranking was F-1 > F-4 > F-3 > F-2, indicating that aluminum was the most preferred fin material when thermal performance, mass, and cost were considered together. The sensitivity analysis also showed that F-1 remained the first-ranked alternative under the examined changes in material prices and criterion weights. The present results can support the selection of a suitable fin material for achieving a balance among thermal performance, system weight, and material cost in latent heat storage applications.