Effect of interfacial nanolayer on thermophoresis in nanofluids

The existence of solid-like nanolayers between nanoparticles and the solvent may play a key role on thermophoresis of nanoparticles in nanofluids. In this paper, by taking into account the graded interfacial nanolayer, we present a two-step method to investigate the thermophoretic mobility of nanoparticles in nanofluids. First, the temperature fields within the particle, the nanolayer, and the base fluid are derived with the steady heat equation. Second, by solving Navier–Stokes equations of fluid motion with the slip boundary condition, we determine the thermophoretic velocity of nanoparticles. The effect of nanolayer thickness, nanoparticle size and the thermal conductivity of particles and base fluid on the thermophoresis of nanoparticles are discussed. We find that the thermophoretic mobility exhibits a non-monotonic dependence on the particle's size. The effect of the temperature on the thermophoretic mobility are further investigated. In addition, our numerical results are in qualitative agreement with the relevant experimental reports.

► In this paper, we adopt a two-step method to aim at the thermophoresis in nanofluids. ► Temperature fields in nanofluids are obtained analytically. ► Thermophoretic velocity is determined by solving Navier–Stokes equations. ► Both the graded nanolayer and particle-solvent interaction are taken into account. ► We find thermophoretic mobility is dependent on particle size, temperature et al.