Viscosity of Fe2O3-water nanofluids by molecular dynamics simulations: Effects of nanoparticle content, temperature and size

Abstract

In this study, Molecular Dynamics (MD) Simulations are used to calculate the viscosity of Fe2O3-water nanofluid within the Green-Kubo framework considering the influence of nanoparticle volume fraction (2.05, 4.08, 6.08 vol%), nanofluid temperature (T = 5, 25, 45 and 65 °C), and size (d = 1, 1.24, and 1.44 nm). First, by screening some existing water models, SPC/E model is found to be the winning candidate for viscosity calculation under the temperature range. Second, the simulation method and parameters for Fe2O3-Water nanofluid interactions are developed and verified against experimental studies. Fe-O (RDF) of Fe2O3 nanoparticle first peak occurs at r = 1.879 Å with the maximum error of 7.4% in comparison to experimental and density functional theory (DFT) reported values. Simulation results show that the viscosity of Fe2O3-water nanofluid is significantly larger compared to that of the water base fluid (>57%). It is also demonstrated that the viscosity of the nanofluid increases with the particle volume fraction and decreases with temperature and size of nanoparticles with local sensitivities of about 0.69, −0.65, and −0.37, respectively. A second order polynomial regression analysis is performed on various volume fractions to express the relationship between the volume fraction and the viscosity. Our results are in agreement with existing experimental results. It was found that the presence of nanoparticles created a structured water layer near the nanoparticle surface, and that the interactions between water molecules and iron oxide nanoparticles were prominent in the Fe_Ow (iron-oxygen of water) pair interactions. Parameters such as SASA (Solvent Accessible Surface Area), surface to volume ratio, moment of inertia around principal axes, radius of gyration, and RDF are used to provide insights into the behavior of Fe2O3-water nanofluids and the underlying mechanisms. To the authors’ best knowledge, this is the first MD simulation of Fe2O3 nanofluids conducted to date.