Research On Preparation And Heat Storage Properties Of Modified Inorganic Molten Salt Heat Storage Materials

Solar energy is easy to use,its clean and pollution-free characteristics make it one of the key energy for sustainable development in China.However,solar energy is not stable and continuous in time and space,thus the key point is thermal energy storage technology and optimization of materials for thermal storage and heat transfer in solar thermal technology.Molten salts are the most used heat carrier and heat storage materials in solar power plants,widely used in a number of countries around the world.Currently nitrate salts can be properly used in low temperature solar applications and carbonate salts can be properly used in high temperature solar applications.But generally,molten salts have low heat capacity and heat conductivity,so this study mainly focus on enhancement of heat capacity and thermal conductivity of heat storage materials.To raise the heat capacity of nitrate hybrid molten salts,in this study,the dispersion of nanoparticles was chosen to achieve the enhancement.On the other hand,the metal foam is chosen to make combination with carbon molten salts by self-infirtration method to raise thermal conductivity.Phase change temperature and latent heat of the materials were measured by DSC methods.Chemical compatibility of metal foam with carbonate salts materials was analyzed by using XRD method.Also,the mechanism of enhancement of heat capacity was illustrated in the aspect of vibration unit.In this study,the heat capacity of NaNO₃-KNO₃-LiNO₃ ternary nitrate eutectic heat storage materials were effectively enhanced by doping SiO₂ nanoparticles.When the mass ratio of nanoparticles is 1 wt%,agglomerations occurred among nanoparticles.But there are still a lot of isolate nanoparticles dispersing in the system,and providing a large specific surface area thus more high energy vibration units which lead the raise of heat capacity in the system.The effect of agglomeration of nanoparticles on heat capacity enhancement was also studied.By using Polyvinylpyrrolidone（PVP）with different concentrations,we reduced the agglomeration of nanoparticles and the dispersity of nanoparticles in nitrate salts was improved which resulted in furtherly enhancement of heat capacity of nitrate salt heat storage materials.Combined with the results above,the mechanism of heat capacity enhancement of nitrate salt materials by doping nanoparticles was illustrated.In this paper a new high temperature phase change thermal storage composite of Li₂CO₃-Na₂CO₃-K₂CO₃-BaCO₃ quaternary carbonate salts with carbon fiber and metal-foam was prepared by using melt infiltration.And XRD,EPMA,SEM,DSC and Laser Flash method were used to analyze its structure,chemical compatibility and thermos-physical characterization.Results show that the Quaternary carbonate and copper foam have excellent chemical compatibility,SEM analysis suggests that carbonate,carbon fiber and metal-foam substrates are united well and carbon fibers form some interface connections.Phase change composite has an endothermic peak at405.42°C which corresponds to the melting point of quaternary carbonate eutectic salts.The phase change composite prepared has high thermal storage density and thermal conductivity.