Particle migration in a flow of nanoparticle suspensions

This paper is concerned with particle migration in pressure-driven laminar pipe flows of relatively dilute suspensions of nanoparticles (nanofluids), one of the most frequently used configuration in industries. The motivation behind the work is associated with the thermal behaviour of nanofluids, which can greatly exceed the values predicted by currently available macroscopic theories. A theoretical model is formulated to predict particle concentration, and velocity field of nanofluids in the transverse plane of the pipe. The model takes into account the effects of the shear-induced and viscosity gradient-induced particle migrations, as well as self-diffusion due to the Brownian motion. It is shown that particle concentration in the wall region can be much lower than that in the central core region. This indicates a highly non-uniform thermal conductivity profile across the transverse plane of the pipe, and thus has a significant implication to heat transfer intensification using nanofluids. The results also suggest the existence of an optimal particle size whereby the thermal conductivity is enhanced with little penalty due to the effect of pressure drop.