Numerical study of thermochemical energy storage characteristics of MgSO4

doi:10.19799/j.cnki.2095-4239.2024.0851

Abstract

Abstract:

A charging/discharging model of a two-dimensional porous medium MgSO₄·7H₂O/MgSO₄ was developed using reaction kinetics to investigate the energy storage characteristics of MgSO₄as a thermochemical material. This study examined the reaction rate, temperature distribution, and water vapor concentration distribution during heat and mass transfer in charging/discharging units. This study also examined the influence of inlet air temperature (T_in) and inlet air velocity (U_in) on unit performance and thermal efficiency. The results indicate that during the charging process, heat storage increases by approximately 3.13% for every 10 ℃ increase in T_in and by approximately 0.97% for every 0.125 m/s increase in U_in. An increase in T_in accelerates the rate of unit heat transfer and enables the water vapor pressure to reach equilibrium faster, subsequently increasing the reaction rate. Similarly, an increase in U_in enhances the water vapor transport rate and improves the convective heat transfer within the unit, thereby enhancing the kinetic properties and increasing the reaction rate, which leads to an increase in the heat storage capacity. Conversely, during the discharge process, the unit thermal efficiency exhibited an inverse relationship with heat storage capacity. The thermal efficiency decreased by approximately 0.93% for every 2.5 ℃ increase in T_in, whereas heat storage decreased by approximately 0.58% for every 0.1 m/s increase in U_in. An increase in T_in increases the equilibrium pressure of the unit and decreases its unit reaction rate, thereby reducing the effect of temperature rise of the unit. Furthermore, an increase in U_in increases the rate of water vapor transport and convective heat transfer of the unit, which subsequently increases the water vapor pressure. Ultimately, the reaction rate and thermal efficiency decreased. This study offers a theoretical foundation and practical reference for understanding the thermochemical energy storage characteristics of MgSO₄.

Key words: MgSO₄·7H₂O, heat and mass transfer, porous medium, thermochemical energy storage

CLC Number:

TK 02

Shuyu XU, Yan WANG. Numerical study of thermochemical energy storage characteristics of MgSO₄[J]. Energy Storage Science and Technology, 2024, 13(12): 4299-4309.

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参数	数值
水蒸气摩尔质量, M_v/(g/mol)	18.02
MgSO₄·7H₂O摩尔质量, M_h/(g/mol)	246
MgSO₄摩尔质量, M_deh /(g/mol)	120
MgSO₄·7H₂O比热容, c_h/[J/(kg·K)]	1546
MgSO₄比热容, c_deh/[J/(kg·K)]	800
MgSO₄·7H₂O渗透率, k_h/m²	5.44×10^-11
MgSO₄渗透率, k_deh/m²	7×10^-11
MgSO₄·7H₂O密度, ρ_h/(kg/m³)	1680
MgSO₄密度, ρ_deh/(kg/m³)	2660
化学计量数,Ψ	6
MgSO₄·7H₂O热导率, λ_h/[W/(m·K)]	0.48
MgSO₄热导率, λ_deh/[W/(m·K)]	0.48
频率因子, A_f/s^-1	167000
活化能, E_a/(kJ/mol)	55
理想气体常数, R	8.314
参考压力, p_ref/Pa	101325
气体扩散系数, D_g/(m²/s)	2.82×10^-5
反应焓, ∆H_r/(kJ/mol)	411
反应熵, ∆S_r/[J/(mol·K)]	1041

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Numerical study of thermochemical energy storage characteristics of MgSO₄

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