Charging of insulating spheres in contact with an electrode affected by a mono-ionized field

The charge acquired by an insulating sphere in an uniform mono-ionized electric field has been accurately evaluated by Pauthenier. In certain electrostatic applications, such as the electroseparation of mixed granular solids, the particles to be charged are in contact with an electrode. Under these circumstances, Pauthenier's formula is no longer valid, because the field is nonuniform. The present paper addresses this problem from both a computational and an experimental point of view. A numerical method of electrostatic field analysis was employed for the evaluation of the charge acquired by spheres of various dielectric constants, in contact with plate electrode. The experiments were carried out on a laboratory equipment provided with various types of corona electrodes. An electrometer was used to measure the charge acquired by calibrated spheres of polyamide (diameter: 3 mm) when subjected to the positive or negative corona discharge generated between these electrodes and a metallic rotating roll electrode (diameter: 150 mm) connected to the ground. The experimental data were in good agreement with the theoretical predictions. The charge of the particles was found to be maximum for a model of electrode, which was then proposed as the standard for the industrial corona-electrostatic separators.

[1]  Alaa A. Elmoursi,et al.  Simulation of space charge in unbounded geometries , 1990 .

[2]  W. B. Smith,et al.  Development of a theory for the charging of particles by unipolar ions , 1976 .

[3]  R. Morar,et al.  Corona - electrostatic separators for recovery of waste non-ferrous metals , 1989 .

[4]  Joseph M. Crowley,et al.  Fundamentals of applied electrostatics , 1986 .

[5]  Decrease in Charge of Sharp-Edged Ellipsoidal Particles by Self-Discharge , 1985, IEEE Transactions on Industry Applications.

[6]  J. Nelson,et al.  Estimation of particulate charging and migration for pulsed precipitator applications , 1987 .

[7]  L. Sparks,et al.  Charge measurements on individual particles exiting laboratory precipitators with positive and negative corona at various temperatures , 1980 .

[8]  M. Pauthenier,et al.  La charge des particules sphériques dans un champ ionisé , 1932 .

[9]  Lucian Dascalescu,et al.  Mathematical modelling of conductive particle movement in d.c. corona fields , 1993 .

[10]  Lucian Dascalescu,et al.  A New Type of Corona Electrode for High - Tension Separators , 1993 .

[11]  Lucian Dascalescu,et al.  Corona and electrostatic electrodes for high-tension separators , 1993 .

[12]  Lucian Dascalescu,et al.  Numerical analysis of the electric field of roll-type electrostatic separators , 1993 .

[13]  L. Dascalescu,et al.  Charging of particulates in the corona field of roll-type electroseparators , 1994 .

[14]  P. L. Levin,et al.  A unified boundary-element finite-element package , 1993 .

[15]  M. Washizu,et al.  Ionic charging of a very high resistivity spherical particle , 1979 .

[16]  K. Adamiak.  Simulation of corona in wire-duct electrostatic precipitator by means of the boundary element method , 1991, Conference Record of the 1991 IEEE Industry Applications Society Annual Meeting.