A rigid spherical particle translating at small tube Reynolds number in a shearing flow experiences lateral migration due to small inertia and wall effect. In a suspension flow of sufficiently small particles, Brownian motion is another factor. In this work, we investigate this migration phenomenon of Brownian particles in a pressure-driven flow for a range of particle volume fractions (φ) much less than 0.01. The flow velocity is varied, which results in bulk Pecle´t number (Pe) ranging over four orders of magnitude. Both the velocity and the particle distributions were measured. It has been found that when Pe is smaller than 1000, particles migrate away from the channel wall, and that the particle concentration in regions remote from the wall (more than 10 particle diameters) is nearly uniform; When Pe increases beyond 1000, particles move toward a preferred position with the migration effect becoming progressively stronger as Pe increases.

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