Molecular dynamics simulations of the microscopic mechanism of thermal conductivity enhancement of ethylene Glycol–Water–Au nanofluids

Abstract

With an increase of the heat load of internal combustion engines, the heat dissipation of the equipment increases accordingly. Traditional ethylene glycol (EG)–water coolants are unable to meet the heat dissipation demands of high heat load internal combustion engines. Nanofluids have better heat transfer performances than conventional fluids, suggesting they can be used to solve the problem of the insufficient heat dissipation capacity of internal combustion engines. In this paper, EG–water–Au nanofluids are formed by adding Au nanoparticles with a volume fraction of 1.5% to EG–water solutions. These are used to investigate the effect of the EG mass concentration on the thermal conductivity of the EG–water solutions and their nanofluids, and to analyze the microscopic mechanism of thermal conductivity enhancement of the nanofluids. It is found that the thermal conductivity of the EG–water solutions are positively correlated with the water content of the system, and the higher the water content of the system, the better the diffusion performance of the system components. The thermal conductivity of the EG–water solutions increase for all EG mass concentrations after the addition of Au nanoparticles, up to 17.20%. The presence of an adsorption layer of base liquid molecules on the surface of the nanoparticles is an important reason for the improved thermal conductivity of the nanofluids. According to the analysis of molecular radius of gyration, end-to-end distance and intermolecular interaction energy in the systems, it is found that the addition of the nanoparticles has no significant effect on the conformation of EG molecular chain, and the van der Waals interaction energy in the nanofluid systems is slightly enhanced. Through an analysis of the radial distribution function and density distribution of the nanofluid systems, it is found that the base liquid molecules that adsorb on the surface of the nanoparticles are stratified. The high-density interval of EG molecules is (0.65, 1.25) nm, while water molecules mostly gather in the form of clusters in the (1.15, 1.65) nm interval, and the arrangement of base liquid molecules in the adsorption layer is similar to the orderly arrangement of solids. The properties of some components in the nanofluids show a solid-like microstructure, which makes the thermal conductivity of the nanofluids higher than that of the base solution. These research results can provide an important reference for improving the heat transfer performance of traditional alcohol–water coolants.