Study of Dust Removal by Standing-Wave Electric Curtain for Application to Solar Cells on Mars

摘要

Multiphase electric curtains generate traveling waves which can lift and convey charged particles, whereas single-phase electric curtains create a standing wave. However, this paper confirms that, in certain conditions, such a standing-wave curtain can expel the deposited powder as well. Indeed, we present results of experiments performed in atmospheric air and in carbon dioxide with electrodes coated with an insulating material for different powders under various pressures down to that existing on Mars $(p cong 7 hbox{mbar})$. Under high-enough pressure in air $(p = 1 hbox{bar})$, a part of the powders is put into motion when raising the applied voltage below the ionization threshold. Above the discharge threshold, the deposited powder can be completely expelled from the stressed zone by the dielectric barrier discharges (DBDs) occurring in the gas just over the surface of the insulating layer. This proves that the charging of particles by collection of gaseous ions and electrons produced by the DBDs is involved in the lift and in the removal of powders. The powder removal becomes more difficult when $p$ is lowered. For gas pressure around 7 mbar, a good powder removal requires a distance between axes of adjacent electrodes lower than 1 mm. The dust removal efficiency also depends on the size of the particles and on the contact between the particles and the substrate. With Mars analog dust being spread out with a brush, the removal of the so-produced agglomerated particles is often satisfactory. When injecting and dispersing the same powder into the vessel under reduced pressure, the layer resulting from particle sedimentation can be removed. However, when the injected tribocharged particles are driven directly onto the standing-wave curtain, the resulting du-n-nst layer remains unperturbed by the action of electric field and DBDs. Very likely, this is due to the intimate contact between the particles and the substrate. These observations are discussed in the light of the different forces acting on particles.