Numerical investigation on melting and solidification in a novel bionic honeycomb-fin triple-tube latent heat storage unit with nanoparticle-enhanced PCM

• Bionic honeycomb-fin design significantly enhances heat transfer and storage performance. • Staggered fin layouts optimize heat-flow pathways and reduce lag regions. • Al 2 O 3 nanoparticle incorporation improves thermal conductivity and accelerates phase change. • Bionic fins combined with NEPCM create a compact LHS unit with boosted heat transfer and efficiency. Latent heat storage (LHS) is crucial for renewable energy utilization and thermal management; however, its performance is often limited by the low thermal conductivity of phase change materials (PCMs). This study numerically investigates the melting and solidification behavior of a bionic honeycomb-fin triple-tube LHS unit using computational fluid dynamics (CFD) in ANSYS Fluent based on the enthalpy-porosity method. Three fin configurations (straight fins, Y-shaped fins, and bionic honeycomb fins) were compared to assess their thermodynamic performance. To further enhance thermal conduction, Al 2 O 3 nanoparticles with volume fractions of 1.0 %, 3.0 %, and 5.0 % were incorporated into paraffin to form nano-enhanced PCMs (NEPCMs). Results show that the optimal bionic honeycomb-fin structure with a staggered internal-external layout (Case f) reduces the melting and solidification times by 45.0 % and 59.3 %, respectively, compared with the conventional straight-fin configuration (Case a). The average heat flux increases from 493.75 to 562.21 W/m 2 during melting and from 318.06 to 491.28 W/m 2 during solidification. Furthermore, the staggered layout (Case f) achieves an additional 3 % and 10 % reduction in melting and solidification times compared with the unidirectional honeycomb-fin arrangement (Case e). Incorporating nanoparticles at a 1.0 % volume fraction (Case f-1) further reduces melting and solidification durations by 15.9 % and 17.7 %, respectively, and enhances the average heat flux by 22.0 % and 20.3 % relative to the fin-only case (Case f). Overall, the combination of bionic fin structures with NEPCMs provides a promising approach for developing compact, high-efficiency latent heat storage systems with improved heat transfer performance and faster thermal response.