Molecular dynamics insight into the best governing mechanism for thermophysical properties changes in nanofluids

Extensive studies on the thermophysical behavior of nanofluids have been conducted so far; however, the mechanisms behind the change in the thermophysical properties of nanofluids remain unclear. In this study, the influences of Brownian motions of nanoparticles, induced micro-convection, interfacial nanolayer and ballistic phonon transport mechanisms on improving the thermophysical and rheological properties of Cu-water nanofluids were investigated using equilibrium and non-equilibrium molecular dynamics simulations. For this purpose, the nanoparticle was dispersed in the base fluid in three different cases: free, fixed and fixed-rigid. Then, the fundamental and nanostructural properties of nanofluids such as fluid velocity contours, number (mass) density, potential energy, temperature gradient inside and around the nanoparticle and random motions of the nanoparticle were analyzed to explore the best mechanism for thermophysical and rheological properties changes in nanofluids. The SPC/E model was used to calculate the interactions between water molecules, while the embedded-atom-method potential was applied for Cu-Cu interatomic interactions. The nanofluids were created by dispersing spherical Cu nanoparticles with a diameter of 2.6 nm in liquid water at 6.5 vol%. The results showed that the shear viscosity and thermal conductivity of nanofluid increased by 38.47% and 6.5%, respectively, compared to the base fluid, while the self-diffusion coefficient decreased by 18.24%. It was also found that the Brownian motion of nanoparticles, ballistic phonon transport and micro-convection mechanisms have no significant effect on the thermophysical properties of nanofluid. According to the results, it was concluded that the formation of the interfacial nanolayer around nanoparticles is the key most important factor in improving the thermophysical properties of nanofluids and the properties of this layer can have a considerable effect on the nanofluid properties. It was explained that the interatomic interactions between the nanoparticle atoms and the base fluid play a key role in forming the interfacial nanolayer structure.

Automated summary

Extensive molecular dynamics simulations were conducted to investigate the influences of various mechanisms on improving the thermophysical and rheological properties of Cu-water nanofluids, and it was found that the formation of the interfacial nanolayer is the key factor for enhancing the properties of nanofluids.