Abstrakt

Recently narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application in diesel engines. In this paper results of 2-dimensional (2D) Particle Image Velocimetry (PIV) measurements of the flow patterns in a narrow ESP for a various electrode geometries are presented. The PIV measurements were carried out in the observation plane that is perpendicular to the ESP duct. The ESP was a glass parallelepiped, 300 mm long, 30 mm wide and 30 mm high. The electrical electrode set consisted of a single wire discharge electrode and either single or two or four plane collecting electrodes. The discharge electrode, made of a stainless steel wire of a diameter of 0.23 mm and length of 100 mm, was placed longitudinally to the flow. The collecting plane electrodes (30 mm x 120 mm) were made of aluminium tape of a thickness of 50 μm glued on dielectric supporting plates. Depending on the electrode geometry, either a single collecting plane electrode was placed on the bottom wall (geometry 1), either two or four collecting plane electrodes were placed on the bottom and top walls (geometry 2), or on the bottom and side walls (geometry 3), or on all four walls (geometry 4) of the ESP. The DC voltage of 10 kV was applied to the wire electrode through a 10 MW resistor, while the collecting electrodes were grounded. Air flow seeded with a cigarette smoke was blown along the ESP duct with an average velocity of 0.9 m/s. The PIV measurements were carried out in a so-called electrode mid-plane, perpendicularly to the wire and the collecting electrodes. The obtained results showed that the particle flow in the ESP had strongly three dimensional (3D) character due to both the applied voltage and narrow cross section of the ESP duct. For the electrode geometries 1, 2 and 3 large and very regular vortex structures were observed in the mid plane. Although our measurements were two dimensional the analysis of the obtained results showed that the observed vortices exhibit three dimensional character, having the form of a spiral vortex moving along the ESP. These spiral vortices may decrease the particles collection efficiency, as it was calculated by Dumitran [1]. However, for the electrode geometry 4 the vortex structures were smaller and irregular, which may results in a different particle collection efficiency. The particle collection efficiency for all presented electrode geometries are under investigation.

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