Simulation on heat transfer and thermal storage processes of gradient foamed metal-PCM microstructure composite

Using paraffin as phase change material (PCM), the melting process of gradient foamed metal composite PCM was numerically simulated. Ten kinds of gradient foamed metal with average porosity of 86 % and average pore density of 10 PPI (1 PPI = one pore per inch) were designed by using a three-dimensional structure model of sixsided through circular hole. The impact of the pore density and porosity of the foamed metal with different gradient parent materials on the heat transfer and heat storage performance of the composite PCM was systematically studied. The results reveal that the heat transfer process of the composite PCM containing gradient foamed metal is mainly affected by heat conduction. The main thermal resistance is located at the bottom layer, and the heat transfer performance could be enhanced by rationally designing the parent material gradient. And even if the entire bottom layer is foamed metal Cu, the main thermal resistance of the composite PCM is still located in the bottom layer. Through a reasonable porosity gradient design, the melting rate could be further accelerated. Compared with the composite PCM containing uniform porosity gradient foam Cu, the complete melting time of the porosity gradient of 0.90-0.86-0.82 can be shortened by 11.30 %. Thermal non-equilibrium phenomenon exists in the composite PCM containing gradient foamed metal. As the pore density of foamed metal located at bottom layer increases, the maximum average temperature difference decreases. A reasonable design of the pore density gradient can better weaken the thermal non-equilibrium phenomenon. Furthermore, the heat storage density per unit mass of the composite PCM containing gradient foamed metal increases with the increase of the average porosity. Compared with the composite PCM containing gradient foamed metal with Ni-Al-Cu parent material, the heat storage density per unit mass is higher in the stable stage and increases more rapidly during the heat storage process in the composite PCM containing uniform gradient foam Al.