Low grade energy recovery for phase change material storage

Latent heat thermal energy storage (LHTES) systems using phase change materials (PCM) are widely applied in waste heat recovery, solar thermal systems, and building energy management. However, their performance is often limited by low thermal conductivity and non-uniform melting. In shell-and-tube systems, buoyancy-driven natural convection creates thermally inactive regions near the bottom of the storage unit. Hence, improving heat transfer while preserving energy storage capacity remains a key design challenge. This study numerically investigates a PCM-based LHTES system with parallel and Y-shaped fins in a double-pipe-in-shell configuration. The objective is to enhance melting in thermally inactive regions. All finned cases are designed with identical fin volumes to ensure comparable PCM volumes. Simulations are conducted under identical operating conditions. No-fin, parallel fin, and Y-shaped fin configurations are analysed, including axially segmented designs. The results show that fin enhancement significantly improves melting performance. Compared to the no-fin case, complete melting time is reduced by approximately 60-65%. Optimised Y-shaped fins provide a further reduction of about 15–25% relative to conventional parallel fins. This improvement is achieved without compromising energy storage capacity. The optimised segmented Y-shaped fin exhibits the best overall performance. Complete melting is achieved in approximately 1220 s. Temperature uniformity is also improved. The enhanced performance is attributed to improved radial heat conduction and stronger buoyancy-driven convection. These mechanisms promote deeper heat penetration into previously inactive PCM regions. Overall, the findings demonstrate that Y-shaped fins offer an effective passive enhancement strategy for PCM-based LHTES systems under constrained material usage. Future work may focus on solidification behaviour, cyclic operation, and techno-economic assessment.