Electrokinetic pumping using traveling wave high voltages

Charge separation near a liquid/solid interface is explored by electrokinetic pumping of Freon TF and transformer oil using high-voltage traveling waves. Fluid-head-displacement measurements show strong dependencies on peak voltage amplitude (1.0-2.5 kV), frequency (0.1-20 Hz), and liquid conductivity (10/sup -13/-10/sup -9/ S/m). For any conductivity, reverse pumping (opposite to the traveling wave direction) occurs when the ratio of the voltage to the frequency is small, but switches to forward pumping when the ratio is large. The greatest displacement occurs when the dielectric relaxation and charge migration times are comparable. Preliminary measurements of average volume charge density, by sampling a portion of the liquid, relate net positive charge to forward pumping and net negative charge to reverse pumping. A charge transport analysis coupled to viscous dominated flow describes some features of the pumping.<>