六水氯化镁脱水蓄热过程的数值模拟

Numerical simulation of heat storage process of magnesium chloride hexahydrate dehydration

六水氯化镁(MgCl_(2)·6H_(2)O)由于较强的吸附能力、低反应焓以及较高的储热效率,成为当今热化学储能常用的材料。建立六水氯化镁脱水蓄热过程二维数值模型,将质量、动量、能量与化学反应物理场进行耦合,研究反应床的温度与转换程度分布,同时对反应器内自由空气流道的布置进行结构优化设计。讨论了入口流体流速和温度、材料孔隙率以及导热系数的影响。研究结果表明较高的热空气入口流速和温度能在一定程度上促进传热,同时也会降低热量利用率。在布置自由流道的情况下,圆柱体自由流道的均等布置能在一定程度上加快反应的发生。高热导率明显提高传热速率,但对于多孔渗流主导、床层内全部填充水合盐的反应器,泡沫金属的添加使总体渗透率减小,反应速率反而降低。

Magnesium chloride hexahydrate(MgCl_(2)·6H_(2)O)has been widely used in thermo-chemical energy storage due to the strong adsorption capacity,low enthalpy and high thermal efficiency.A two-dimension numerical model of MgCl_(2)·6H_(2)O dehydration and heat storage process was established,in which the mass,momentum,energy and chemical reaction equations were coupled to study the temperature and conversion extent distributions of the reaction bed,and the effects of the inlet airflow velocity and temperature,as well as material porosity and the coefficient of thermal conductivity on the heat and mass transfer and reaction kinetics were also discussed.The results show that higher hot air inlet velocity and temperature can promote heat transfer to a certain extent,but in the cases that the heat utilization will be reduced and heat loss increases.When the free flow channels are arranged in salt bed,the equidistance arrangement of the cylindrical free flow channels can accelerate the reaction rate to a certain extent and reduce the completion time in dehydration.The high heat conductivity can obviously enhance the heat transfer,but the heat transfer is deteriorated in the case of foam metal adding,and the overall reaction rate is decreased finally in the porous reaction bed filled with hydrated salt,as the slow seepage worsens heat transfer and the overall permeability is reduced in porous salt bed.