Numerical investigation on the melting of nanoparticle-enhanced phase change materials (NEPCM) in a bottom-heated rectangular cavity using lattice Boltzmann method

Abstract

Convection melting of water (ice)–copper nanoparticles as a nanoparticle-enhanced phase change material (NEPCM) in a bottom-heated rectangular cavity is investigated numerically in this paper. A novel lattice Boltzmann (LB) method is developed to solve the solid–liquid phase change coupled with natural convection, in which two sets of evolution functions (density evolution function and temperature evolution function) are constructed to simulate fluid flow and heat transfer. The latent heat source term in temperature evolution function is treated with an implicit scheme, avoiding iteration steps as compared with previous methodologies. The moving melting interface is treated with an immersed moving boundary scheme, which makes it simple for the implementation of non-slip velocity condition on the solid–liquid interface. The predictions of the current model are compared with previous numerical and experimental results, and a reasonable agreement is obtained. And then the developed model is employed to study the impacts of the volume fraction of nanoparticles and the Grashof number on the flow structure and heat transfer characteristics. The computed results show that the NEPCM exhibits high heat transfer efficiency in comparison to the pure phase change material (PCM). As the volume fraction of nanoparticles increases, the temperature field and melting interface evolves faster, and the melt fraction and energy stored increases. In addition, for high volume fraction of nanoparticles at a Grashof number Gr = 2.5 × 10 5 , an asymmetric melting interface forms due to the asymmetric distribution of the convection cells.