Study On Preparation Technology And Properties Of High Temperature Phase Change Composite Heat Storage Materials

At present,the deteriorating global environment has aroused widespread concern,and the development of green energy is imminent.Heat storage technology is an important technology for developing green energy,and phase change materials play a decisive role in heat storage technology.Molten salt/ceramic composite phase change materials has became a research hotspot in the field of heat storage materials because of its low cost and good heat storage performance.However,in practical application,the problems of pulverization and leakage of molten salt/ceramic composite phase change heat storage material restrict its development.In this study,the thermophysical properties and microstructure of Na2CO3,K2CO3 and Na2CO3-K2CO3 eutectic salts were simulated by molecular dynamics using Born-Mayer potential function.The variation trend of specific heat capacity,thermal expansion coefficient,self diffusion coefficient and density with temperature,and the distance between Na,K,C and O atoms at different temperatures were analyzed.The results show that Na2CO3-K2CO3 eutectic salt is a high temperature phase change heat storage medium with excellent comprehensive properties.Based on the Na2CO3-K2CO3 eutectic salt heat storage medium,the chemical stability of different matrix(calcined MgO,diatomite and steel slag)and Na2CO3-K2CO3 eutectic salt was studied,the thermophysical properties of the prepared composites were deeply studied.The results show that the calcined MgO matrix material and Na2CO3-K2CO3 eutectic salt have good chemical stability,and the prepared composite heat storage material has excellent properties.This paper reveals that the moisture absorption behavior is the main reason for the pulverization and collapse of the structure of Na2CO3-K2CO3/MgO composite phase change materials.The soluble Na2CO3-K2CO3 eutectic salt plays a connecting role between MgO particles in the composite phase change materials,and the Na2CO3-K2CO3 eutectic salt dissolves after moisture absorption,which leads to the disappearance of the material bonding strength,and finally causes the pulverization and collapse of the material.A new structure of high temperature molten salt/ceramic phase change materials with moisture absorption and pulverization resistance is proposed.The water-insoluble silicate reinforcer was used to enhance the bonding strength between MgO particles,and a new matrix structure with skeleton structure was constructed,while the Na2CO3-K2CO3/reinforcer/MgO composite phase change heat storage materials with moisture absorption and pulverization resistance and stable shape were successfully prepared.It has good heat storage performance,thermal stability and cyclic heat storage exothermic performance,with latent heat storage of 58.4J/g and latent heat release of 58.2J/g and the total heat storage is 785.4J/g.The reason of molten salt leakage of high temperature molten salt/ceramic phase change composite heat storage material is also analyzed in this paper,and a new method of embedding sintering film with encapsulant is proposed.The Na2CO3-K2CO3/reinforcer/MgO phase change composite heat storage material with anti leakage coating is successfully prepared by diatomite encapsulant.Diatomite encapsulation agent and eutectic salt form a water-insoluble coating,which can prevent water from entering the material,so as to prevent the leakage of molten salt.