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

ABSTRACTA 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 (ks) 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 ks 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.KEYWORDS: Salt hydratethermochemical heat storageporous matrixadsorptionvacuum impregnation Nomenclature W=Adsorption capacity or water uptake per unit mass (g/g)m0=Initial mass of sample (g)m=Sample mass (g)t=Time (min)T=Temperature (℃)ks=Kinetic constant (s−1)X=Dimensionless adsorption capacityNad=Normalized absorption capacityNde=Normalized desorption capacitySubscripts=0=Initial momenteq=Equilibriums=Time(s)th=theoreticalad/de=adsorption/desorptionAbbreviations ASC=AA impregnated MgSO4 and MgCl2AA=Activated AluminaAS=AA impregnated MgSO4AC=AA impregnated MgCl2TCHS=Thermochemical heat storageDSC=Differential scanning calorimeterHSD=Heat Storage DensityBET=Specific surface areaHR=Relative HumiditySEM=Scanning Electron MicroscopyXRD=X-ray diffractionDisclosure statementNo potential conflict of interest was reported by the author(s).Data availability statementThe data that support the findings of this study are available from the corresponding author upon reasonable request.Additional informationFundingThis research was supported by Key Research and Development and Promotion Projects in Henan Province (Science and Technology Research) [212102310411, 232102320201].Notes on contributorsXueling ZhangXueling Zhang is faculty in the department of Energy and Power Engineering, Zhengzhou University of Light Industry, China. Her research interests are thermochemical materials and thermochemical energy storage systems, heat and mass transfer mechanism of porous media.Junheng GuJunheng Gu is a postgraduate student of the School of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are thermochemical energy storage materials and numerical simulation.Qiang YeQiang Ye is a postgraduate student of the School of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are the numerical simulation of thermochemical energy storage and the mechanism of heat and mass transfer.Yeqiang ZhangYeqiang Zhang is faculty in the department of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are the waste heat utilization and energy storage system, heat and mass transfer mechanism.Qi ZhangQi Zhang is faculty in the department of Energy and Power Engineering, Zhengzhou University of Light Industry, China. Her research interests are phase-change energy storage materials and energy storage systems.Chuanxiao ChengChuanxiao Cheng is faculty in the department of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are phase-change energy storage materials and energy storage systems.Haoyun XunHaoyun Xun is a postgraduate student of the School of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are the thermal chemisorption energy storage materials and the numerical simulation of the system.Tingxiang JinTingxiang Jin is faculty in the department of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are phase change energy storage materials and energy storage system, refrigeration system energy saving.Jianxiu LiuJianxiu Liu is faculty in the School of Mechanical and Electrical Engineering, Zhengzhou University of Light Industry, China. Her research interests are advanced material forming and testing technology.Xuehong WuXuehong Wu is the Professor of the School of Energy and Power Engineering, Zhengzhou University of Light Industry, China. His research interests are phase-change energy storage materials and energy storage systems, enhancement of heat and mass transfer.