Heat Transfer Optimization in Irregular Enclosures with Nano-Encapsulated Phase Change Materials: A Hybrid LB–FDM Numerical Analysis

This numerical study examines free convection heat transfer in an irregularly shaped cavity filled with a phase-change material nano-encapsulated in water mixture at a volume fraction of 3.5%. A hybrid computational approach integrating the lattice Boltzmann method for fluid dynamics with the finite difference scheme for heat transfer is utilized. The influences of the normalized fusion temperature θf, wall energy strength χ, wall thickness 𝛿, and Rayleigh number Ra on flow structure, phase change behavior, and thermal performance are systematically analyzed. The results indicate that intermediate fusion temperatures (θf≈0.3-0.4) provide an optimal interaction between natural convection and latent heat absorption, leading to enhanced NEPCM melting and higher average Nusselt numbers. Increasing wall energy strength and wall thickness promotes more uniform melting and improves thermal regulation within the cavity. In addition, higher Rayleigh numbers intensify convective motion, accelerate phase change, and further enhance heat transfer. These findings highlight the effectiveness of NEPCM-based fluids for improving thermal management in natural convection systems.