Experimental evaluation of the migration of spherical particles in three-dimensional Poiseuille flow

Convective transport of 10 mum nearly neutrally buoyant spherical particles (polystyrene vinyl dibenzene) is studied in 220 mum and 530 mum diameter capillaries using an on-line particle detector of the electronic gate type. The detector, connected to the capillary outlet, monitors the elution and translates the passage of individual particles into pulsed signals. The measuring technique requires the use of an electrically conductive carrier liquid, such as physiological saline (0.9%NaCl). Passage times are registered for discrete capillary lengths varying between 0.25 m and 5 m. Mean particle and fluid velocities are used to calculate the preferential radius of particle transport. The equilibrium position of the particles is found to shift towards the capillary wall for higher Reynolds numbers, for longer and smaller capillaries, and for more dilute suspensions. However, the higher the particle to capillary diameter ratio, the more pronounced wall effects. Moreover, as the Stokes number is small (E-2), adhesion at the capillary walls turns out to be non-negligible and to have an impact on the final quantitative results. (C) 2004 American Institute of Physics.