Pore-scale study of thermal responses in composite phase change materials with different graphene substrates

The graphene units, with the advantages of excellent thermal conductivity, good toughness, low density, and high connectivity, play a role in enhancing heat conduction. The porous characteristics of the graphene substrates have a significant impact on the heat transfer performance of the composite materials intended for energy storage and heat dissipation applications. Nevertheless, the solid–liquid phase change mechanisms within the generally used graphene substrates, such as two-dimensional (2D) ordered configuration and a three-dimensional (3D) random foam-like arrangement, remain inadequately understood. In this study, two stochastic reconstruction methods were proposed to reconstruct the realistic structure of the 2D and 3D graphene, respectively. Then, the 3D pore scale Lattice Boltzmann method (LBM) based on the total enthalpy method was developed to explore the melting characteristic in both 2D and 3D graphene structures. The numerical results indicate that the vertical thermal conductivity of the 2D structure is markedly superior to that of the 3D foam structure, especially in the case of high porosity (0.95), which is six times that of the 3D structure. For the 3D foam structure, the phase change process exhibits consistency in both horizontal and vertical orientations. The process can be categorized into three distinct regions: an initial rapid phase change region dominated by conduction, a phase change retardation region, and a slow phase change region dominated by natural convection. For the 2D ordered configuration structure, the melting behavior is quite different. When heated vertically, the melted phase change materials show a radial distribution, and the distribution of the phase interface is consistent when the porosity ranges from 0.8 to 0.9. When heated horizontally, the phase interface is perpendicular to the bottom surface. In particular, as porosity reached 0.9, the melting time required was 12.6 times longer compared to that in other porosities. This study contributes to a deeper understanding of how the structural characteristics of graphene substrates influence the internal phase transformation processes in composite materials, thereby providing valuable insights for the optimal design of composite graphite-based materials.