Melting evaluation of a thermal energy storage unit with partially filled metal foam^*

This paper introduces a novel strategy on enhancing melting heat transfer for a shell-and-tube unit by partially filling porous foam. A series of filling ratios for metal foam are studied regarding thermal energy charging performance. A two-dimensional axial-symmetric model is established and verified by comparing of temperature with experimental data, obtaining satisfactory agreement between the two methods. The characteristics of the melting process such as melting fraction, temperature response and uniformity, heat storage and velocity field are analyzed in detail. The results show that the appropriate reduction of the metal foam filling ratio in the upper part can significantly promote the heat storage process due to mainly the enhanced natural convection effect. By comparing 17 cases with different filling ratios, an optimal filling ratio of 0.89 is recommended to achieve a 10.5% higher heat storage efficiency than the one with fully filled condition. The temperature uniformity first increases and then decreases with metal foam filling ratios. The best temperature uniformity is achieved for the filling ratio of 0.95. The case with a filling ratio of 0.89 possesses the shortest energy charging time at the expense of reducing the temperature uniformity. Compared with the fully filled metal foam, a better energy storage process was achieved with less metal foam material.