This paper aims to demonstrate the thermodynamics of a thermal storage system based on the latent heat of a composite Phase Change Material (PCM). The paper investigates the flow and heat transfer of solid-liquid phase transitions at the pore level using the Lattice Boltzmann method. The phase transitions process is described using the enthalpy method. A porous medium at the pore scale is constructed here by binarization processing of photograph. The single phase change process is compared with phase transitions in porous media. The simulation results indicate that during the whole heat transfer process, the conduction effect dominates in porous medium composite phase materials while the convection effect has a remarkable influence on a single phase change process. A temperature difference is found between the aluminum foams and phase change materials. Phase transitions in pored aluminum with different porosity are also simulated to validate the feasibility of the enthalpy model at the pore scale.