Two-dimensional lattice Boltzmann simulation of colloid migration in rough-walled narrow flow channels

A lattice Boltzmann model was used to simulate the accelerated transport of dense inert particles in low Reynolds number flows in smooth- and rough-walled narrow channels. The simulations showed that, after an initial transient, an initially immobile particle migrated faster than the average fluid velocity. The sensitivity of the particle residence time to wall roughness increased with decreasing Reynolds numbers. The relationship between the exit position and residence time of a particle was sensitive to the release position, flow strength, and the wall roughness. A particle with a density 5% larger than the density of the fluid migrated to an equilibrium position between the centerline and the wall for the slowest flow rates in rough-walled channels, displaying the Segre-Silberberg effect that a rigid neutrally buoyant spherical particle exhibits in small Reynolds number flows. However, a particle that was 35% denser than the density of the fluid drifted to the centerline in the slowest flows due to the gravitational settling effect. The difference in the residence time of the less-dense and dense particles was most sensitive to the surface roughness at the smallest Reynolds number investigated.