Effects of shape and ratio of copper foam on thermal storage properties of the heat storage system with phase change materials

Latent heat storage technology can be used to overcome the instability of solar-powered equipment. However, the poor thermal conductivity of phase change materials markedly weakens the thermal storage efficiency of the heat storage system. Filling copper foam is a valid method to improve the thermal conductivity of phase change materials. To explore the synergistic effect of copper foam filling shape and ratio on the thermal storage performance of the heat storage system, the present study researched the thermal storage performance of the heat storage system with different copper foam filling ratios under two types filling shapes using myristic acid and copper foam as feedstocks. The mechanism of the influence of the ratio and shape of copper foam on the heat storage performance was discussed from Rayleigh number and natural convection velocity. The results show that there is a linear relationship between the ratio of copper foam and the thermal storage performance for the compact stacking shape. The melting time is shortened by 32.8 % and the heat storage efficiency is increased by 45.1 % when the content of copper foam increases from 10 % to 50 %. For the spaced stacking shape, the ratio of copper foam has a non-linear relationship with the thermal storage performance, reaching a maximum at 40 % copper foam filling ratio. Compared with the control group, the full melting time is shortened by 38.53 % and the heat storage efficiency is increased by 64 %. As the ratio of copper foam increases from 10 % to 50 %, the Rayleigh number increases from 208 x 103 to 188 x 103 and the convection velocity decreases by 47.8 % to 66 %. The average convective velocity of spaced stacking shape is 2 % to 38 % lower than that of compact stacking shape under the same ratio of copper foam.