Electrohydrodynamic behaviour of single spherical or cylindrical conducting particles in an insulating liquid subjected to a uniform DC field

The author presents a theoretical study of the electrohydrodynamic motion of single conducting particles (spheres or cylinders) in an insulating fluid between horizontal plane-parallel electrodes subjected to a DC voltage. These particles, when in contact with the bottom electrode, acquire a charge and, after `lift-off' proceed to bounce up and down. The laws of particle velocity and the current - voltage relationships are established for the three possible hydrodynamic régimes of motion (viscous, intermediate and inertial) in the bulk according to the Reynolds number of particles. The phenomena taking place in the vicinity of the electrodes (field-enhancement and microdischarges) are analysed and quantified via numerical computations performed with a charge-simulation program. An experimental investigation has been performed with large (millimetre) steel particles in an insulating oil. Charges and velocities deduced from measured lift-off voltages and transient currents are in good agreement with the predicted values. The apparent charge transferred in the microdischarges is in accord with the numerical calculations.