Molecular Dynamics Simulations of the Effects of a Nanoparticle Surface Adsorption Layer on the Thermal Conductivity of a Cu–Ar Nanofluid

Abstract

Nanofluids formed by adding a small volume fraction of solid nanoparticles to the conventional fluid can greatly enhance the thermal transport performance of the conventional fluid. This study reveals the mechanism of thermal conductivity by studying the microscopic effect of nanoparticles in a Cu–Ar nanofluid on the base fluid. Due to the presence of a trapped, adsorbed Ar layer on the surface of the nanoparticle, under certain volume fractions, the influence of the nanoparticles with different sizes on the thermal conductivity is analyzed. The equilibrium molecular dynamics and nonequilibrium molecular dynamics methods are used to calculate and verify the thermal conductivity of the nanofluid, and the abilities of the Lennard–Jones (LJ) and embedded atom method (EAM) potential functions to accurately describe interactions between Cu atoms are compared. By calculating the contribution of different components to the thermal conductivity of the nanofluid, it is found that the composition of the base liquid plays a leading role, while the nanoparticle composition and the solid–liquid cross-section contribute very little. Through decomposition of the Green–Kubo formula (contains potential energy term (V), the kinetic energy term (K), the collision term (V)), it is found that the PV, KV, and VV terms are related to collisions (V) when the LJ potential function is used, which play a major role in the nanofluid’s thermal conductivity. Partial enthalpy terms h, PP, and KK contribute little to the thermal conductivity, and they hinder any decrease of the thermal conductivity as the size of the nanoparticles increases; meanwhile, the KP term remains basically constant. In systems described by the EAM potential function, the contributions of KP and PP are relatively high. Therefore, this paper analyzes the mechanism of increasing the thermal conductivity of Ar-based nanofluid from the perspective of molecular dynamics simulation and obtains the results.