Numerical simulation on thermal behavior of partially filled metal foam composite phase change materials

As a kind of material with high thermal conductivity, metal foam embedded in phase change materials (PCM) can significantly improve the thermal energy storage performance of PCM, so as to better serve the latent heat thermal energy storage (LHTES). However, the presence of metal foam will suppress the natural convection of PCM, reduce its LHTES capacity and increase the total cost. In view of the above problems, this study designed LHTES units with metal foam filled at the top or the bottom with different height ratios. The melting heat transfer characteristic was studied by numerical simulations. Results show that the flow rate of liquid paraffin in the bottom filling configuration is one to two orders of magnitude higher than that in the top filling configuration, which plays a positive role in natural convection and is more conducive to heat transfer enhancement. However, the top filling configuration performs better in the heat storage capacity. The metal foam with a filling height ratio of 0.75 can increase the heat storage capacity by 7.47% while saving 25% material. On this basis, we proposed a new criterion, named the comprehensive strengthening goodness factor (CSGF), for evaluating the heat transfer performance of LHTES system. CSGF is different from the general criterion in that it can evaluate the heat storage capacity and the economic performance at the same time. Under the evaluation of CSGF, the optimum metal foam-paraffin configurations for different occasions were selected.