SINGLE-PARTICLE FLOW DYNAMICS IN SMALL PORES BY THE RESISTIVE PULSE AND THE PRESSURE REVERSAL TECHNIQUE

A new modification of the resistive pulse technique has been used to study experimentally flow dynamics of single polystyrene spheres in an electrolyte flowing back and forth through a pore. Pore diameters have been close to 30 μm. Our newly developed pressure reversal technique allows detailed studies of particle flow properties in a size range relevant to flow in porous media. By pressure drive, a particle enters a current-carrying pore and an increase in resistance proportional to the particle volume is detected. When a particle exits the pore, the pressure is reversed such that the particle reenters the pore. The interplay between particle sedimentation outside the pore and radial migration (particle motion transverse to streamlines) inside the pore has been investigated. When particle sedimentation is a small perturbation, the measured evolution of the transit time as the particle migrates in Poiseuille flow compares well with an empirical relationship for the migration velocity first proposed by Segré and Silberberg (1962) and later verified by Ishii and Hasimoto (1980). A rather large perturbation outside the pore is needed before the particle flow behavior deviates substantially from pure radial migration. © 1990.