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

Abstract

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.

Crater Formation on Electrodes during Charge Transfer with Aqueous Droplets or Solid Particles

“…Analysis of the recorded video to determine the corresponding acquired charge (by balancing the electrostatic force versus the drag force) indicates that the metal ball typically receives about 70 pC to 250 pC of charge from either electrode depending on the applied field strength, while the droplet receives approximately 110 and 200 pC from the negatively and positively charged electrode respectively. The overall behavior of the droplets and metal balls, including the magnitude of charge acquired, is broadly consistent with previous studies [9,14,18,19,24]. Examination of 50-nm thick electrodes after electrically bouncing a water droplet reveals no changes visible to the naked eye.…”

“…Although similar light flashes have been previously observed when charged objects [13,14] or liquid drops [26] approached an electrode, recent workers have assumed that electrically bouncing droplets are charged via electrochemical reactions not involving dielectric breakdown [18,19]. It is known from previous work that application of an arc current on the order of 1-100 amps between stationary electrodes through vacuum can melt the electrodes via Joule heating, with the high pressure present in the plasma jet of the arc pushing the molten material to form micron-scale craters [27,28].…”

Metallic nanowires and mesoscopic networks on a free surface of superfluid helium and charge-shuttling across the liquid–gas interface

“…The recharging of the particles at the lower electrode probably proceeds via the micro-breakdown in the gap between the electrode surface and approaching nanoparticle. 29,37 The breakdown is expected there because of a very large local electric field enhancement in the vicinity of the nanoparticle. The breakdown is started at some critical particle-electrode distance that increases with the applied electric field strength.…”

Wireless Monitoring of Workpiece Material Transitions and Debris Accumulation in Micro-Electro-Discharge Machining

“…Debris are created naturally during the discharge process, but problems occur when it is not flushed out of the discharge gap efficiently. The presence of debris can lead to spurious discharges, causing the discharge gap to increase, tool dimensions to decrease, and machining precision to be reduced [11], [12]. In batch-mode μEDM, this is very problematic because the path for debris to escape can be quite tortuous and becomes worse as feature density is scaled up [2].…”