Numerical study of thermochemical energy storage characteristics based on MgSO4

doi:10.19799/j.cnki.2095-4239.2024.0851

Abstract

Abstract:

A charging/discharging model of the two-dimension porous medium MgSO₄·7H₂O/MgSO₄ is built based on reaction kinetics to study the energy storage properties of the thermochemical material MgSO₄. Reaction rate, temperature distribution and water vapor concentration distribution during heat and mass transfer process in the charging/discharging unit are analyzed. The effects of inlet air temperature (T_in ) and inlet air velocity (U_in ) on the characteristics of the unit and thermal efficiency are analyzed.The results show that, for the charging process, heat storage increases by approximately 3.13% for every 10 ℃ increase in T_in . While heat storage increases by approximately 0.97% for every 0.125 m/s increase in U_in . The increase in T_in results in a faster rate of unit heat transfer and the water vapor pressure reaches equilibrium pressure more quickly. Consequently, the rate of reaction increases. The increase in U_in accelerates the water vapor transport rate and enhances the convective heat transfer within the unit, strengthening its kinetic properties and increasing the reaction rate, leading to an increase in the heat storage capacity.For the discharging process, the trend in unit thermal efficiency is the opposite of the heat storage capacity. Thermal efficiency decreases by approximately 0.93% for every 2.5 ℃ increase in T_in . While heat storage decreases by approximately 0.58% for every 0.1 m/s increase in U_in . The increase in T_in increases the equilibrium pressure of the unit and decreases the unit reaction rate, reducing temperature rise effect of the unit. The increase in U_in increases the rate of water vapor transport and convective heat transfer of the unit, increasing the water vapor pressure. Ultimately, the reaction rate and thermal efficiency are decreased. This study provides a theoretical basis and reference for the thermochemical energy storage properties 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 based on MgSO₄[J]. Energy Storage Science and Technology, doi: 10.19799/j.cnki.2095-4239.2024.0851.

Figures/Tables 17

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

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Numerical study of thermochemical energy storage characteristics based on MgSO₄

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