The lateral migration of neutrally-buoyant spheres transported through square microchannels

The lateral migration of neutrally-buoyant particles transported through square microchannels has been experimentally investigated over a Reynolds number range of 0.06 <= Re <= 58.65 at the ratio of channel hydraulic diameter to particle size, lambda approximate to 14. Flow Reynolds numbers are determined by applying a conventional particle-tracking algorithm to small tracer particles, while novel imaging techniques have been proposed for identifying and defining the measurement depth of large test particles. By analyzing the spatial distributions of spherical particles, it is revealed that lateral migration of particles markedly occurs even at very low Re, which is induced by the high shear rate due to the small-scale effect. The particle equilibrium position is obtained as a function of Re, and the critical Re at which the particle equilibrium position starts to increase is found in the range 20 <= Re <= 30. The outermost edge of the particle cluster is also in good agreement with previously available data, which provides a good quantitative basis for designing microfluidic devices that are to be used for plasma separation from whole blood.