Molecular dynamics simulation of the effects of SiO2 nanoparticles on thermophysical properties of low concentration salt solution fluid

The effect of nanoparticles on the heat transfer mechanism of the fluid is still unclear. In the present study, a 5 wt.% NaCl solution was modeled and different sizes of spherical SiO₂ nanoparticles were added to the model to analyze the effects of the nanoparticles on the thermophysical properties of the system based on the calculated results, in order to better understand the relevant mechanism. Current research reveals the interfacial interactions and layering phenomena that lead to variations in thermophysical parameters. The higher the peak of the radial distribution function (RDF) of Si-Cl⁻ is, the higher the order of the ionic layer, and the better the energy storage effect of the ionic layer would be. The van der Waals energy of the system reflects the strength of the interionic forces within the system, and its trend is similar to that of specific heat capacity. The narrower the width of the RDF peak is, the thinner the ionic layer, the lower the interfacial thermal resistance (ITR), and the higher the thermal conductivity would be. The addition of SiO₂ nanoparticles inhibits the diffusion of the matrix fluid. Due to the enhanced interactions between ions in the matrix fluid, the viscosity of fluid increases accordingly. The addition of 6 wt.% SiO₂ nanoparticles increases the maximum viscosity by 18.7 %. However, when the system density is sufficiently large, the collision frequency of ions in the system increases, leading to an increase in the mean square displacement. An increase in SiO₂ nanoparticle concentration reduces the average displacement and peak RDF of the system, thereby decreasing the thickness of the ionic layer on the nanoparticle surface. The formation of the ionic layer enhances the ITR between the nanoparticle and fluid. Therefore, when the RDF decreases, the ITR of the system also decreases. When the ITR decreases by 26 %, the thermal conductivity of the nanofluid increases by 4.5 %.