Effect of pore density and filling ratio of metal foam on melting performance in a heat storage tank

Abstract

Thermal energy storage through solid–liquid phase change is an efficient method for mitigating solar energy intermittency by providing continuous energy supply for the end-users. However, the low thermal conductivity of phase change material, which serves as the heat transfer medium in the thermal energy storage systems, severely undermines the heat charging/discharging rates. Metal foam can significantly strengthen the heat storage performance via increasing the thermal conduction capability of phase change material and metal foam composite, mainly due to the large extension surface area and highly-conducting metallic ligaments of the metal foam. To squarely explore the influence of the two vital parameters (filling ratio and pore density) for the metal foam upon the phase change process, numerical models for describing the phase change process in a tank filled with phase change material and metal foam are established, and the experimental validations of the corresponding models are performed. Melting time, temperature uniformity, and heat storage capacity are selected as the targeted indexes for assessing and evaluating the impacts of filling ratio and pore density on the phase change process. The results show that the full melting time of heat storage decreases first and then increases with the decrease of filling ratio under any PPI. The smaller the PPI, the smaller the overall heat storage time. And the larger the PPI, the greater effect of the filling ratio on the heat storage time. The melting time of the PCM under the optimal filling ratio of 10 PPI and 100 PPI is shortened by 8.06% and 18.06%, and the temperature uniformity is reduced by 5.48% and 10.11%, respectively, compared with that of the complete filling.