Thermal energy storage performance of magnesium-based hydrated salts impregnated with activated alumina

Abstract

ABSTRACT A new thermochemical heat storage composite was prepared for the first time by vacuum impregnation using activated alumina (AA) as the porous matrix and magnesium sulfate (MgSO4) and magnesium chloride (MgCl2) as the heat storage material. The salt content of composites obtained by the vacuum impregnation method was 8.31% higher than that of atmospheric impregnation method. The adsorption and heat storage performance were investigated, the AA − 20 wt% MgSO4 (AS-20) and AA − 20 wt% MgCl2 (AC-20) were outstanding from the single-salt-impregnated composites, especially AS-20 with the heat storage density (HSD) increased by 20.7% compared with atmospheric immersion method. Morphological tests and composition analyses were indicated that the hydrated salt was evenly impregnated into the uniform spherical particles AA matrix. A binary mixed-salt (MgSO4-MgCl2) impregnated AA composites were also prepared, and the sample with the MgSO4:MgCl2 mass ratio of 20:80 in the 20 wt% solution (ASC-20) exhibited the better performance. The adsorption capacity of ASC-20 was 0.301 g/g, the kinetics constant (k s ) was 0.01 s−1, and the HSD was 554 kJ/kg, which were higher than those obtained by single-salt composite and atmospheric impregnation methods. In particular, the k s value of ASC-20 was increased by more than 10 times compared to previous studies. After 10 cycles of testing, the HSD of ASC-20 decreased by 12.5%, and no fracture occurred in the globular particles, showing good thermal stability and structural stability. The new composites obtained by this method is conducive to system application.