Preparation and Properties of Phase Change Energy Storage Composites Based on Modified Fly Ash

Fly ash (FA) is a porous solid waste produced by coal-fired power plants that can be used as a carrier for solid–liquid phase change materials (PCM). Due to the disadvantages of FA, including small adsorption capacity and poor thermal performance, its application range is limited. Therefore, FA modification methods have received increasing attention. Two modification methods were used to improve the adsorption capacity of FA. After the modification experiments, the surface structure of modified fly ash (MFA) was eroded, revealing a three-dimensional porous structure. The Al/Si mass ratio of the alkali-modified sample increased from 0.67 to 1.28, and the specific surface area and pore volume increased from 3.82 m2/g and 0.008 cm3/g to 40.86 m2/g and 0.026 cm3/g, respectively. The shape-stable phase change material (SSPCM) prepared using the hybrid sintering method of Al-12Si alloy and alkali-modified fly ash (MFA-OH) exhibits excellent thermal properties and thermal cycling stability. The results showed that the heat storage density and thermal conductivity of SSPCM increased with an increase in PCM content. The thermal conductivity and latent heat of phase change in the composite with the highest latent heat of phase change in the sample were 18.24 W/(m·K) and 124.10 J/g, respectively. The optimum loading rate for the alloy is 65 wt%. After 100 thermal cycles, the latent heat and thermal conductivity of the phase change at SSPCM were 93.3% and 94.6% of the initial values, respectively. The research findings provide a feasible process for FA as a phase change carrier, and the application scope is extended.