Experiment And Numerical Study On The Thermochemical Heat Storage Based On Hydrate Composite Materials

In solar thermal utilization,thermal storage technology is an important technical to overcome the solar energy volatility and intermittent.According to the difference of heat storage mechanism,heat storage technology is divided into sensible heat storage,latent heat storage and thermochemical heat storage.Among them,the thermochemical heat storage technology has the advantages of long heat storage period,less heat loss and large heat storage density.It is also a hot spot at home and abroad.Aiming at the thermochemical heat storage of hydrated salt composites,this paper carries out the following two aspects:First,the experimental study of a high stability magnesium sulfate-zeolite composite heat storage material.In the material preparation process,it was found that the content of magnesium sulfate in the specific surface of the zeolite also increased as the concentration of the magnesium sulfate solution increased.However,when the concentration of magnesium sulfate solution is increased to 20%,the composite material will be precipitated with magnesium sulfate during the adsorption process,which is not conducive to long cycle recycling of the composite material.The surface morphology and material composition of the composites were characterized by scanning electron microscopy and XRD.It was found that magnesium sulfate was uniformly dispersed on the surface of zeolite,and no chemical reaction between magnesium sulfate and zeolite resulted in new material.The experimental characterization also found that the specific surface area and the average pore size of the composite material adsorption has a greater impact.Finally,DSC tests show that the composite has a heat storage density of up to 419 J/g at 15%magnesium sulfate.Second,numerical simulation was carried out to study the desorption endothermic process of magnesium chloride particles packed bed and the exothermic adsorption process of magnesium chloride particle packed bed.A thermal non-equilibrium model of porous media was established to simulate the flow,heat transfer and mass transfer between magnesium chloride and water vapor during the adsorption/desorption process.Based on the experimental verification of the reliability of the model,the two-step desorption and thermal storage process of magnesium chloride hexahydrate were studied numerically.The results showed that the particles which reached a certain temperature started to desorb the crystallization water during the heat storage process of solid particles packed bed of magnesium chloride hexahydrate,and the desorption reaction proceeded in two steps.Finally,four crystal water,Heat storage process is completed.The results of adsorption-heat exothermic simulation of the packed bed of magnesium chloride dihydrate show that adsorption of heat with low temperature and humid air into the reactor leads to the increase of temperature of solid particles and further heating of the air.When heated,the air heats the particles at the rear of the reactor and accelerates the adsorption reaction.Finally,the influence of reaction constant on the exothermic process of magnesium chloride dihydrate was discussed.The results show that increasing the reaction constant will speed up the reaction and increase the temperature of the reactor outlet.