Molecular simulation of viscosity of nanofluids based on water with metal particles

Abstract

Shear viscosity coefficient of water-based nanofluids with copper particles is simulated with the molecular dynamics method. The interaction of water molecules with each other was modeled with Lennard-Jones potential. The viscosity coefficient was calculated on the basis of the fluctuation-dissipation theorem by the Green–Kubo formula. The selection of parameters of the potential corresponding to the experimental values of water viscosity and density at a given temperature of 25°C at the atmospheric pressure is performed. Rudyak–Krasnolutskii (RK) and Rudyak–Krasnolutskii–Ivanov (RKI) potentials described interaction between nanoparticles and water molecules and nanoparticles with each other, respectively. Diameters of copper nanoparticles used were 2 and 4 nm. Volume concentration of the nanoparticles varied from 1% to 5%. It is shown that the viscosity of the nanofluids exceeds significantly the viscosity of suspensions with macroscopic particles and increases with a decrease in the size of nanoparticles at a fixed volume concentration. The paper also presents the calculation data of pair distribution functions for pure water and nanofluid. It is shown that the water near the nanoparticle is much more structured than in the free volume. This large ordering in the nanofluids is one of the key factors of their higher viscosity compared to pure water.