Preparation and characteristic of wood-based inorganic composite phase change material with effective anisotropic thermal conductivity for thermal energy storage

The thermal energy storage technology based on phase change materials (PCMs) can solve the mismatch problem between thermal energy supply and demand, and improve energy utilization efficiency. However, the fluid leakage problem and low thermal conductivity of PCMs are not suitable for solar thermal storage application. The solar thermal collector combined with PCM seeks for the rapid storage of thermal energy and reduces the heat exchange with external environment, requiring PCM to possess specific directional thermal conduction. In this paper, inspired by the principle of directional transport of water in the cellulose channel of natural trees, the porous structure with anisotropic thermal conductivity is formed by carbonization of pine at 1000 degrees C. The CPCM with directional thermal conductivity is prepared by combining magnesium nitrate hexahydrate (MNH) with carbonized wood (CW). The axial thermal conductivity of the MNH/CW composite PCM (CPCM) is 1.86 times than that of the radial direction. The photo-thermal conversion efficiency of MNH/CW CPCM is 83%. This structure changes the direction of thermal energy transmission, and reduces the dissipation of thermal energy and the use of thermal insulation medium. This work provides an innovative idea for the design and manufacture of CPCM related to low and medium temperature solar thermal energy storage.