Wall Effects on the Brownian Movement, Thermophoresis, and Deposition of Nanoparticles in Liquids

Abstract

It is well known that the hydrodynamic drag on particles is significantly enhanced close to a plane or curved boundary. This enhancement impedes the movement of the particles in both the parallel and the normal directions with respect to the wall. In the presence of a temperature gradient, the Brownian movement of particles induces the phenomenon of thermophoresis, which results in the steady motion of the particles toward the colder domains of the flow field. This paper examines the effect of the enhanced wall drag on the thermophoretic movement of the nanoparticles in a Newtonian fluid, at short distances (0–10 radii) from a flat, horizontal wall. The effect of the flow shear lift on the thermophoretic motion of the particles close to a horizontal wall is also examined. It is observed that the movement of the particles toward the plane wall is significantly retarded because of the enhanced drag and that it, actually, causes particle accumulation close to the plane wall. It is also observed that the lift, which is induced by the relative Brownian movement, does not have an effect on the average motion of particles toward the wall and does not play an important role on the deposition of particles.