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 Ram in a range of 150 ∼ 600 is investigated. The results suggest that, with the increase of Ram 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.