Particle migration in nanofluids considering thermophoresis and its effect on convective heat transfer

The effects of particle migration on concentration distribution and convective heat transfer coefficient of the water-TiO2 nanofluid were investigated inside a circular tube. The concentration distribution was obtained considering thermophoresis, non-uniform shear rate, Brownian diffusion and viscosity gradient. Using the scale analysis, it was demonstrated that thermophoresis can have a significant effect on the particle migration. Dispersion approach was used for simulation, while a non-uniform concentration was applied. An experimental study was conducted to examine the numerical solution accuracy and there was a good agreement between the experimental and numerical results. Non-uniformity of the concentration is intensified by increasing the Reynolds number and the particle size. Thermophoresis makes the concentration more non-uniform and the velocity profile flatter as well. At greater mean concentrations, the effect of thermophoresis on particle distribution and convective heat transfer coefficient is highlighted. Meanwhile, considering thermophoresis yields greater convective heat transfer coefficient in all Reynolds numbers.