Effect of filling height of metal foam on improving energy storage for a thermal storage tank

Heat storage eliminates the imbalance of supply and demand for renewable energies. Metal foam holds phase change materials (PCMs) inside the porous network through both enhancing conduction and enlarging heat transfer area. To synergically utilize the buoyancy convection in the molten PCM as well as the heat conduction penetration by the porous matrix, a partially filling configuration on the metal foam was proposed to enhance the energy efficiency for the storage tank. Numerical models were established and verified by comparing with experimental results. Metal foams with five different porosities were filled in the tank, under nine filling ratios ranging from 60% to 100% in an interval of 5%. By evaluating the melting characteristics of the different cases, the influences of both the filling ratio and porosity upon the melting performance were analyzed. Results demonstrated that there existed an optimal filling ratio to maximally reduce the complete melting time, and this ratio decreased with an increase in porosity. The full melting time under a high porosity of 0.98 was the least affected by different filling ratios. However, excessively reducing the filling ratio significantly retarded the melting process regardless of the filling porosities. Upon saving 5% mass for the metal foam, a reduction of 15.7% in complete melting time was achieved. The partially filling design provided a competitive solution to thermal applications by improving the energy storage efficiency and reducing the material consumption.