Evolution of Electrohydrodynamic Flow of Suspended Particles in a Needle-to-Plate Negative DC Corona Discharge in Air
J. Mizeraczyk1, A. Berendt2, J. Podliński2, and A. Niewulis2,3
1Department of Marine Electronics, Gdynia Maritime University, Poland
2Centre for Plasma and Laser Engineering, The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences, Poland
3Mathematics Teaching and Distance Learning Centre, Gdańsk University of Technology, Poland
Abstract- Corona discharges are used for collecting dust in electrostatic precipitators (ESPs). The dust collection is mainly realized by the electric forces which move the ionized dust particles to the collecting electrodes. However, the presence of corona discharge in the space between the charging and collecting electrodes in ESPs causes also the so-called ionic wind which set the gas molecules and dust particles in motion. As a consequence, a secondary electrohydrodynamic (EHD) flow is formed, which affects the 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 flow of the air and suspended dust particles in a needle-to-plate DC corona discharge arrangement, simulating an ESP. The measurements were mainly focused on the time period just after the corona discharge onset. The experimental apparatus for our study of EHD flow 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 end of which had a tapered profile with the tip having a radius of curvature of 75 µm. The interelectrode distance was 25 mm. Negative voltage of 8 kV was supplied to the needle electrode. An acrylic box, with the needle-to-plate electrode arrangement inside, was filled 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 electrode arrangement. They clearly show the formation of a ball-like structure of the particle flow at the needle tip and its evolution into a mushroom-like object moving with an average velocity of about 2.5 m/s towards the collecting electrode. This movement initiates a flow of the seeded air from the needle-tip vicinity into the space between electrodes. Then the EHD flow develops into two very regular vortices, rotating in opposite directions, and eventually the regular vortices disappear.
Keywords-DC corona discharge, EHD flow, flow measurement, PIV