Shear-induced diffusion in dilute suspensions

Abstract

The particle and fluid interactions that occur in dilute suspensions of non-colloidal particles in shear flow are examined in this thesis. In the theoretical and experimental studies described here, a range of intriguing mechanisms that give rise to particle and fluid diffusion in these suspensions are elucidated.

While shear-induced migration of particles in suspensions has been studied for several decades, most studies in the past have focused on concentrated suspensions. The mechanisms that lead to particle and fluid migration in concentrated suspensions vanish in the dilute limit. However, many other mechanisms play a significant role only at low particle concentrations.

The confining walls of a sheared dilute suspension give rise to particle and fluid diffusion even at large separations from the walls. Here, the diffusivities arising due to the this mechanism are predicted for smooth and rough spheres. This mechanism is also experimentally studied by observing the motion of particles and fluid in sheared suspensions. The experimental study of particle flux due to gradients in concentration is used to determine the diffusivity arising from the interaction of the roughness elements on the surface of particles.

An intriguing and previously unknown mechanism of fluid dispersion arising due to the translation of spheres in shear flow is also described in this thesis. Analogous to this case, a mechanism of fluid dispersion due to forced translation of spheres that are located in the close proximity to a wall is also described. It is shown that this mechanism can give rise to fluid mixing many particle radii away from the wall when non-neutrally buoyant particles are allowed to settle along the walls in the presence of shear flow.