Melting enhancement in Shell-and-tube latent heat storage device with double-deck Y-fins

A novel double-deck Y-shaped longitudinal-fin configuration was experimentally evaluated for melting enhancement in a shell-and-tube latent heat storage device. A transparent shell-and-tube test rig containing paraffin was used to compare the proposed configuration with conventional straight fins at comparable fin volumes. The solid–liquid interface evolution was directly visualized, while temperatures were measured at 15 locations distributed in the axial, radial, and circumferential directions under different HTF inlet temperatures, flow rates, and flow directions. Despite a 3.6% lower fin volume, the Y-shaped configuration provided 2.92 times the surface area of the straight fins, produced a flatter melt front, and mitigated axial thermal stratification. Over the five HTF inlet temperatures of 60–80 °C, its mean temperature response rate was 108–176% higher than that of the straight-fin unit. Averaged over these five conditions, the Y-shaped fins reduced the temperature non-uniformity index by 55.8% and the time to quasi-steady state by 45.1%. Reversing the HTF flow direction changed the time required to reach a given temperature by less than 150 s at the monitored locations. Increasing the HTF flow rate accelerated heating, but the incremental benefit diminished at higher flow rate. Increasing the inlet temperature also accelerated heating and melting, although it increased spatial temperature non-uniformity. Overall, the proposed Y-shaped fins enabled faster and more uniform charging than straight fins under the investigated conditions, demonstrating their effectiveness in enhancing melting heat transfer in shell-and-tube latent heat storage devices.