Thermal Properties And Enhancement Mechanism Of Molten Salt-based Silica Nanofluids

In this paper,Si02 nanopowder was synthesized by Stober method,and the influence of ageing time on products was discussed.Copper nanoparticles were loaded on the surface of silica by chemical method,which enabled the twin hydroxyls to be observed.Nano fluids which contain 1wt%nanoparticles were made by two-step method,and the obtained samples were analyzed by both SEM and DSC-TG.Moreover,the influence of experimental conditions,such as the temperature of evaporation and the calcination temperature on the products’ morphology and thermal properties were discussed.The results show that,during the synthesized process,both the particle size and the amount of products increase with the prolonging of ageing time.It can be assumed that during the process of particles growth,new silica nucleation happens in liquid at the same time.The homogeneous distribution of the twin hydroxyl groups can be observed with the help of copper nanoparticles loaded on the surface of the Si02 nanoparticle.The results also show that,various evaporation temperatures can affect morphology and specific heat capacity significantly.When liquid in mixture is evaporated at 200℃,the nanoparticles were found to disperse uniformly in the based eutectic salt,and the grains of the salt were irregular with similar size.Compared to the based salt,this sample enhances the specific heat capacity of about 25%.For the calcination samples,it seems that the calcination temperature is connected closely with the melting point of pure eutectic salt.The calcination temperature lower than the melting point can lead to agglomeration of nanoparticles,while the calcination temperature higher than the melting point can exert more influences on morphology of pure salt.In comparison with the sample without calcination,the specific heat capacity of nano fluids show a decrease.