Abstrakt

Corona discharges are used for collecting dust in electrostatic precipitators (ESPs). The dust collection is mainlyrealized by the electric forces which move the ionized dust particles to the collecting electrodes. However, the presence of coronadischarge in the space between the charging and collecting electrodes in ESPs causes also the so-called ionic wind which set the gasmolecules and dust particles in motion. As a consequence, a secondary electrohydrodynamic (EHD) flow is formed, which affectsthe primary flow of the dust-polluted gas and the collection of the dust particles.In this communication we present images and velocity field maps and showing the temporal and spatial evolution of the EHD flowof the air and suspended dust particles in a needle-to-plate DC corona discharge arrangement, simulating an ESP. The measurementswere mainly focused on the time period just after the corona discharge onset. The experimental apparatus for our study of EHDflow consisted of a needle-to-plate electrode ESP, high voltage power supply and standard 2D Particle Image Velocimetry (PIV)equipment.The needle-to-plate electrode arrangement consisted of a needle (1 mm in diameter) electrode made of a stainless-steel, the endof which had a tapered profile with the tip having a radius of curvature of 75μm. The interelectrode distance was 25 mm. Negativevoltage of 8 kV was supplied to the needle electrode. An acrylic box, with the needle-to-plate electrode arrangement inside, wasfilled with air seeded with dust particles (incense smoke).The flow and velocity field (PIV) images, recorded just after the corona discharge onset (in intervals from tens to hundreds ms)illustrate the temporal and spatial evolution of the EHD flow (air and the suspended particles) between the needle-to-plate electrodearrangement. They clearly show the formation of a ball-like structure of the particle flow at the needle tip and its evolution intoa mushroom-like object moving with an average velocity of about 2.5 m/s towards the collecting electrode. This movement initiatesa flow of the seeded air from the needle-tip vicinity into the space between electrodes. Then the EHD flow develops into two veryregular vortices, rotating in opposite directions, and eventually the regular vortices disappear.

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