Interplay between interfacial layer and nanoparticle dispersion in molten salt nanofluid: Collective effects on thermophysical property enhancement revealed by molecular dynamics simulations

Abstract

As the primary heat storage materials and heat transfer fluids, the molten salts are widely utilized in concentrating solar power systems. In recent studies, adding nanoparticles has become a conventional and important way to improve heat transfer and storage properties of molten salt materials. In this study, the collective effect of multiple magnesium oxide (MgO) nanoparticles on the thermophysical and structural properties of ternary molten nitrite/nitrates salt (Hitec) and were investigated by molecular dynamics (MD) simulations. The simulation results show that the enhancement of heat storage and transfer grows as the number of nanoparticles increases in general, and such enhancement can be ascribed primarily to the highly ordered adsorption structure formed at the solid-liquid interface, while the mass transfer was slowed down accordingly. The enhancement of thermal conductivity and heat capacity of nanofluids reaches 9.1 and 1.0% before a sudden increase in viscosity, when addition of nanoparticles is 10.2 wt%. However, further analysis show that the degree of nanoparticle dispersion could be also an important parameter for determining the thermophysical properties of the nanofluid. The degree of dispersion can affect the stability of the adsorption layer, as well as the tendency of nanoparticle agglomeration. These findings have provided theoretical support for the development of molten salt nanofluids, and also suggest the importance of considering nanoparticle dispersion when studying the nanofluid with MD simulations, which is usually ignored.