Advanced Fin Design for Efficient Heat Transfer in Double‐Pipe Latent Heat Thermal Storage: A Comparative Study of Straight and Inclined Multielement Fins

The inherently low thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems hampers efficient heat transfer during melting and solidification processes. This study aims to enhance PCM thermal performance by optimizing fin geometry within a vertical double‐pipe heat exchanger, with a focus on inclined multielement fin configurations. Novelty lies in the systematic investigation of fin orientation (30°, 35°, and 40°), number, thickness, and flow direction through detailed two‐dimensional axisymmetric simulations using ANSYS Fluent. The model incorporates buoyancy‐driven convection via the Boussinesq approximation and has been validated against experimental benchmarks with <3% deviation. Results reveal that an inclined three‐element fin configuration at a 40° angle (Case 3‐3) outperforms conventional straight fins (Case 0), increasing melting rate by 6.5% (48.16 W vs. 45.24 W) and reducing melting time by 2.3% (2470 s vs. 2529 s). During solidification, Case 3‐3 also demonstrates superior performance with a 20.8% higher discharging rate (35.42 W vs. 28.05 W) and 18.4% shorter solidification time (3497 s vs. 4352 s). Excessive fin thickness (up to 1.2x baseline) and suboptimal flow direction were shown to reduce performance by up to 25.5%. These findings provide critical insights for thermal system designers by demonstrating how geometric tailoring of fins can substantially boost energy storage and retrieval rates in PCM‐based systems. The proposed configurations offer a practical route to more compact, efficient, and responsive LHTES systems for renewable heating, industrial recovery, and building applications.