Investigation on latent heat energy storage using phase change material enhanced by gradient-porosity metal foam

Utilizing an optimized gradient porosity can help with the temperature uniformity and alleviate the temperature aggregation. In this paper, a solid-liquid lattice Boltzmann (LB) model at the representative elementary volume scale (REV-scale) is established to investigate the enhancement mechanism of gradient porosity on LTES units. Three gradient porosity including Chinese-fan-shape, vertical and concentric distribution has been investigated. The findings demonstrate that a well-designed gradient porosity can significantly decrease the melting time, with the best performance observed when using a fan-shape arrangement of a certain gradient. In comparison to a homogeneous porosity, the fan-shape arrangement of a specific gradient reduces the melting time by 36.1 % and ensures a more uniform temperature distribution. Increasing the number of layers from two to five has no remarkable improvement on melting, not exceeding 4.4 % in total melting time. Conversely, increasing the porosity gradient leads to an increase in melting time of no less than 36.1 %. Furthermore, an extended dimensionless number Ra-m in a range of 150 similar to 600 is investigated. The results suggest that, with the increase of Ra-m the temperature aggregation is more significant, and the gains in melting rate are unable to offset the increased heating temperature's impact on the melting time.