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

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.

KEYWORDS:

• Salt hydrate
• thermochemical heat storage
• porous matrix
• adsorption
• vacuum 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 capacity
Nad	=	Normalized absorption capacity
Nde	=	Normalized desorption capacity
Subscripts	=
0	=	Initial moment
eq	=	Equilibrium
s	=	Time(s)
th	=	theoretical
ad/de	=	adsorption/desorption

Abbreviations

ASC	=	AA impregnated MgSO4 and MgCl2
AA	=	Activated Alumina
AS	=	AA impregnated MgSO4
AC	=	AA impregnated MgCl2
TCHS	=	Thermochemical heat storage
DSC	=	Differential scanning calorimeter
HSD	=	Heat Storage Density
BET	=	Specific surface area
HR	=	Relative Humidity
SEM	=	Scanning Electron Microscopy
XRD	=	X-ray diffraction

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This research was supported by Key Research and Development and Promotion Projects in Henan Province (Science and Technology Research) [212102310411, 232102320201].

Notes on contributors

Xueling Zhang

Xueling 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 Gu

Junheng 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 Ye

Qiang 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 Zhang

Yeqiang 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 Zhang

Qi 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 Cheng

Chuanxiao 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 Xun

Haoyun 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 Jin

Tingxiang 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 Liu

Jianxiu 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 Wu

Xuehong 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.