Patterns of Airflow in Circular Tubes Caused by a Corona Jet With Concentric and Eccentric Wire Electrodes

Abstract

A computational investigation is conducted to study the patterns of airflow induced by corona discharge in the cross section of a circular tube. The secondary flow induced by corona wind in various flow passages has been the subject of numerous investigations. The flow patterns are often identified by multiple recirculation bubbles. Such flow patterns have also been anticipated for circular cross sections where the corona discharge is activated by an electrode situated at the center of the cross section. In this investigation, it is shown that, contrary to public perception, a symmetric corona discharge does not generate a secondary flow in circular cross sections. This investigation then proceeds to demonstrate that the flow responsible for thermal enhancements in circular tubes often reported in the published literature is induced only when there is a slight asymmetry in the position of the electrode. The present computations are performed in two parts. In part one, the electric field equations are solved using the method of characteristics. In part two, the flow equations are solved using a finite-volume method. It is shown that the method of characteristics effectively eliminates the dispersion errors observed in other numerical solutions. The present computations show that the flow in the eccentric configuration is characterized by a corona jet that is oriented along the eccentricity direction and two recirculation zones situated on either sides of the jet. In addition to the computational approach, a number of analytical solutions are presented and compared with the computational results.

Modelling of electrohydrodynamic (EHD) flow in a cylindrical precipitator with eccentric wire electrode

“…The values of velocity shown in Fig. 5 and 6 are smaller than those arising from the data presented in [2], where absolute values of velocity are not given directly, but in terms of u e and Re EHD . EHD Reynolds number obtained there for V 0 = 10.5 kV is 8145.…”

“…Excellent agreement between our and analytical results is seen. The results from [2] differ significantly. They obtained that the charge density drops to zero on the collecting electrode.…”

“…The comparison of the charge density distributions along r (the distance from the wire electrode centre) is shown in Fig. 2, where results from [2] are also presented. Excellent agreement between our and analytical results is seen.…”

“…It was shown recently [2] that the EHD flow observed experimentally in such a system [3] does not occur when the electrode arrangement is perfectly symmetrical; however even a small degree of asymmetry, which is always present in real systems, can induce such flow. Numerical calculations presented in [2] showed that the eccentricity , defined as the ratio of the displacement of the wire electrode d to the tube radius r t (Fig. 1) even as low as  = 0.5% can cause a noticeably flow.…”

“…We performed calculations for similar conditions as in [2] but using COMSOL Multiphysics software [4], which applies a finite element method to solve partially differential equations. We assumed that the system is axially uniform and there is no axial gas flow and solved a set of fully coupled equations for the following variables: the charge density, electric potential, gas velocity and pressure.…”