Biomimetic fractal fins for enhanced thermal performance in fin-and-tube latent heat energy storage

This study experimentally investigates the thermal performance of a novel biomimetic fractal-fin configuration designed to overcome the low thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems. Two heat exchangers with identical copper tube layouts, fin mass, and PCM volume were fabricated to isolate the effect of fin geometry: a benchmark design using conventional planar fins and a novel configuration employing a branched fractal-fin structure. Experiments were conducted at charging inlet temperatures ranging from 65 to 75 °C and discharging inlet temperatures from 10 to 20 °C, with heat transfer fluid flow rates of 1.0 to 2.0 L/min. The fractal-fin geometry enhanced thermal performance by more uniformly distributing fin material and increasing fin–PCM interfacial area, reducing thermal resistance during both melting and solidification. Compared with the planar-fin configuration, the fractal-fin heat exchanger achieved up to 50 % and 67 % higher charging and discharging powers, while the charging and discharging times were reduced by up to 37 % and 44 %, respectively. In addition, the time-averaged overall heat-transfer coefficient increased by up to 55 % during charging and 70 % during discharging relative to the planar-fin design. These gains were achieved without increasing fin mass or reducing PCM volume, indicating that the enhanced performance is driven by the improved heat-transfer pathways and a larger effective heat-transfer surface provided by the fin geometry, while preserving compactness and storage capacity. This highlights fractal fins as a compact and effective enhancement strategy for LHTES, enabling faster thermal response.