Multi-Branch Y-Shaped Fins for Accelerated Melting in Shell-And-Tube Latent Heat Storage: An Integrated 2D Geometric Screening and 3D Operating-Condition Study

The low thermal conductivity of phase-change materials (PCMs) remains a primary barrier to rapid charging in shell-and-tube latent heat thermal energy storage (LHTES). This work proposes a hierarchical multi-branch Y-shaped fin network with extended conductive pathways and evaluates its performance through a two-stage numerical framework, including two-dimensional (2D) geometric screening of fin topology and arrangement followed by three-dimensional (3D) simulations under practical operating conditions. The enthalpy-porosity method and the Boussinesq approximation are used to resolve transient melting and buoyancy-driven convection in RT35 paraffin. In the 2D comparison, the optimized multi-branch topology improves temperature uniformity and advances the melting front more effectively than finless and straight-fin structures, reducing complete melting time by 68.6% and 41.4%, respectively. Rotational arrangement further affects the coupling between conductive paths and natural-convection cells; the best arrangement shortens melting time by 29.8% relative to alternative layouts. In the 3D model, increasing inlet velocity from 0.06 to 0.16 m/s reduces melting time by 44.3% but produces limited gains in stored energy, indicating diminishing returns at high flow rate. Increasing inlet temperature from 333 to 363 K is more influential, reducing melting time by 47.9%, increasing stored energy by 10.6%, and raising average heat-flux density from 500.10 to 1062.16 W/m2. The results demonstrate that the hierarchical branched fin network accelerates thermal charging by redistributing and extending conductive pathways, while inlet temperature governs both melting kinetics and final storage capacity.