Study On High Temperature Stability Of Phase Change Thermal Storage Materials

Many inorganic salts are prone to come about the leakage of molten salt during phase transition,which not only pollutes the environment,but also affects the heat storage properties of the phase change materials and then results in a decrease in the service life.In order to overcome this shortcoming,inorganic salt/ceramic based phase change materials are prepared by compounding inorganic salts with magnesium oxide,silica,clay and other matrix materials.In this paper,eutectic Na2CO3-K2CO3 salts and MgO were compounded with one or two of nano-SiO2,nano-AIN,kaolin,glass powder and nano-graphite to prepare a new phase change heat storage material by mixed sintering method to prepare a new phase change heat storage material.And its high temperature stability was studied.In this paper,when the doping content of nano-SiO2 was less than 10%,the melting point of phase change materials decreased.And doping of kaolin/glass powder and nano-SiO2/AlN can also reduce the melting point of the material.Moreover,the doping of nano-SiO2,kaolin,glass powder and nano-graphite did not affect the latent heat.When the doping amount of nano-AIN was less than 5%,the latent heat did not change significantly.In this paper,in order to study the high-temperature stability of the composite phase change materials,long-term heat preservation experiments were carried out,and the mass change during heat preservation and the melting point and phase change latent heat after heat preservation were analyzed.The following conclusions were drawn:(1)The doping of nano-SiO2-nano-AIN,kaolin,glass powder and nano-graphite can reduce the mass loss and improve the high-temperature stability of the material during long-term heat preservation.For nano-SiO2 and nano-AIN,when the doping amount of nano-powders was 13%.the effect of high temperature stabilization was the best.(2)Kaolin can ensure the stability of the melting point of phase change materials during long-term heat preservation.(3)For the doping amount of nano-SiO2 and nano-AIN,the change of latent heat was the smallest when the doping amount was 10%and 3%,respectively,which was about 21.96J/g.(4)During long-term heat preservation,the average loss rate of latent heat can be controlled within 0.18 J/(g·h)by doping kaolin.In this paper,the doping of nano-SiO2 and AIN.which can reduce the particle size of eutectic salts and promote the sintering of samples through promoting the diffusion of the surface atoms of nano-particles and MgO particles in the calcination process,reduce the mass loss in-the thermal insulation process of samples and improving the high-temperature stability of samples.Kaolin,which can form pore in the particles through the movement of lamellar structure during the calcination process,can protect molten salt,and then reduce the loss of molten salt.Both the cohesiveness of glass powder and the thermal conductivity of nano-graphite can assist kaolin and further enhance the high-temperature stability of materials.