Thermodiffusion in model nanofluids by molecular dynamics simulations

TL;DR

This study introduces a new molecular dynamics simulation method to analyze thermodiffusion in nanofluids, revealing how nanoparticle and solvent properties influence thermophoretic behavior and thermal conductivity.

Contribution

A novel algorithm for computing single particle thermodiffusion in nanofluids using Non-Equilibrium Molecular Dynamics simulations is proposed and validated.

Findings

Thermodiffusion amplitude decreases with nanoparticle concentration.

Thermal diffusion coefficient is independent of nanoparticle size.

Diffusion coefficient increases with solvent quality and bond stiffness.

Abstract

In this work, a new algorithm is proposed to compute single particle (infinite dilution) thermodiffusion using Non-Equilibrium Molecular Dynamics simulations through the estimation of the thermophoretic force that applies on a solute particle. This scheme is shown to provide consistent results for simple Lennard-Jones fluids and for model nanofluids (spherical non-metallic nanoparticles + Lennard-Jones fluid) where it appears that thermodiffusion amplitude, as well as thermal conductivity, decrease with nanoparticles concentration. Then, in nanofluids in the liquid state, by changing the nature of the nanoparticle (size, mass and internal stiffness) and of the solvent (quality and viscosity) various trends are exhibited. In all cases the single particle thermodiffusion is positive, i.e. the nanoparticle tends to migrate toward the cold area. The single particle thermal diffusion 2 coefficient is shown to be independent of the size of the nanoparticle (diameter of 0.8 to 4 nm), whereas it increases with the quality of the solvent and is inversely proportional to the viscosity of the fluid. In addition, this coefficient is shown to be independent of the mass of the nanoparticle and to increase with the stiffness of the nanoparticle internal bonds. Besides, for these configurations, the mass diffusion coefficient behavior appears to be consistent with a Stokes-Einstein like law.