Numerical investigation on thermal performance of phase change materials embedded in functionally graded metal foam

Latent heat thermal energy storage (LHTES) technology based on phase change materials (PCMs) embedded in metal foam has recently become a popular method to store thermal energy and release it to other processes with thermal energy demand, which has been applied in solar energy, electronic devices, waste heat recovery, etc. In this study, we proposed a novel design of metal foam with porosity changing over the horizontal and vertical coordinates. The thermal resistance model method was applied to explore the heat transfer mechanism and linear porosity was proved to be able to improve the convection intensity in different stages of melting. Also, metal foam with horizontal linear porosity or vertical linear porosity can both shorten the total melting time and increase the average power density, while composite linear porosity can combine the enhancing effect of these two structures and achieve an optimal enhancing effect. The optimal linear porosity gradient can enhance the average power density by 15.8 % compared to those of uniform porosity. Furthermore, the heat storage performance of linear porosity with different enclosure aspect ratios was also discussed. The linear porosity structure was proved to be able to balance the nonuniformity of melting caused by natural convection.