Investigation on Latent Heat Energy Storage Using Phase Change Material Enhanced by Gradient-Porosity Metal Foam

•An optimized gradient porosity distribution which could reduce the total melting time by 36.1% compared with homogeneous porosity.•An optimized gradient porosity distribution which could alleviate the “temperature aggregation” phenomenon.•The porosity gradient dominates the melting rate rather than the number of layers. It is not suggested to irrationally increase the layers.•In the range of Ram = 150 ∼ 600, with the increase of Ram, the temperature aggregation phenomenon is more significant, which hinders the further increase of melting rate. Ram = 150 leads to a better temperature uniformity and melting rate.