Electro-osmotic flow in porous media using magnetic resonance imaging

Magnetic resonance imaging (MRI) has been used to study electro-osmotic flo w in a porous medium consisting of spherical glass particles ranging from 2 .0 to 4.0 min in diameter. Electrodes placed at each end of a 1-cm glass tu be containing the spheres and solution were used to generate flow. Pulsed f ield gradient MRI at 500 and 600 MHz was used to measure the fluid velocity fields and provided in-plane image resolution of approximately 78 x 78 mum (2) for 100 mum thick slices. Velocity fields as functions of applied volta ge were measured for four cases: (1) empty tube with open ends, (2) empty t ube with closed ends, (3) tube with packing and closed ends, and (4) tube w ith packing and open ends. Both closed-tube systems showed recirculation; i n the closed tube with particles, recirculation occurred over the length sc ale of a single particle. The standard deviation or spread of the velocity distribution for the closed-tube experiments scaled approximately linearly with increasing applied voltage, while the velocity mean remained approxima tely zero. In the open-tube system, both the mean velocity and the standard deviation of the velocity distribution scaled linearly with the applied vo ltage. Detailed analyses of the velocity distribution histograms show discr epancies with predictions of the bundled-capillary tube, model of electro-o smotic flow in porous media.