Removal of powders from cavities in contaminated surfaces by shock and plasma generated by an adjacent electro-static discharge

An electrostatic discharge (ESD) produced between pin electrodes above a cavity filled with powder is explored as means of contactless removal of particles from contaminated surfaces. The ESD is produced by discharging a capacitor through an air gap. Glass beads of different sizes serve as model powders filling cavities of different depths. Masses of both loaded and ejected powders are measured. The motion of the ejected particles is studied using high-speed video. Most of the ejected particles move vertically up with the initial velocities varied from ca. 4 to 11 m/s. Changing the mechanical properties of the substrate holding the powder does not significantly affect the velocities of the ejected particles. For powders removed from cavities as a result of interaction with the shock and plasma produced by ESD, the number of particle layers ejected is determined by the particle size and the ESD energy, but is not significantly affected by the cavity depth. A single ESD pulse can be effective in the complete removal of powder particles from relatively shallow, 0.2-mm deep cavity. Estimates suggest that the particles are primarily ejected due to the lift forces produced by local velocity gradients of the gas above the loaded powder layer.