Influence of the geometrical parameters of a dielectric barrier discharge reactor on the subsequent tribocharging of granular polymers

International audienceTribocharging of insulating materials is a pivotal step in several electrostatic applications in which the charge value has an important consequence on the outcome of the process. The Dielectric Barrier Discharge (DBD) at atmospheric pressure is an excellent energetic plasma source having the aptitude to change surface properties and, thereby, to enhance triboelectric charging of granular insulating materials. This paper aimed to investigate the influence of dielectric barrier geometrical parameters on the triboelectric charge of the DBD-treated Polypropylene (PP) and Polyvinyl Chloride (PVC) mm-size granules. The studied parameters include the air gap between the upper barrier and the surface of the granular layer, the number of granular layers, as well as the material forming the dielectric barrier and its position. After being treated for 3 s, the granules were triboelectrically charged in a vibratory device for 2 min. The charge the DBD-treated and untreated particles acquire by tribocharging was measured using a Faraday pail connected to an electrometer. Experimental results show that the air gap and the properties of the dielectric barrier can influence the mean value of the discharge current and enhance significantly the triboelectric charge of DBD-treated granules. Best results were obtained when the air gap did not exceed 4 mm and material with high permittivity was used as a barrier

Corona discharge as affected by the presence of various dielectric materials on the surface of a grounded electrode

International audienceThis paper is aimed at the characterization of the corona discharge generated from a high-voltage wire electrode facing a grounded plate that carries dielectric layers composed of granules, sheets, and non-woven media. Current-voltage and current-frequency characteristics were measured, respectively in DC and AC modes, for several values of the thickness of the PE granular layer, PET sheets and PP non-woven media considered in the present study. The measurements show that the corona onset voltage and the behavior of the current-voltage characteristics are dependent on both nature and thickness of the dielectric layer. Both the estimated capacitive component and the ionic component in AC mode vary with the amplitude and the frequency of the voltage. The ionic component is particularly affected by material non-uniformity

Electrostatic separation of peeling and gluten from finely ground wheat grains

Sieving and air classification are not efficient enough for the extraction of the high-nutritional-value constituents of wheat. The aim of this article is to validate a simple electrostatic separation method of peeling and gluten, which are two such nutriments contained in finely ground wheat grains. The electrostatic separator is composed of metallic grounded belt conveyer and a rotating roll electrode connected to a high voltage supply. The electrostatic behavior of peeling and gluten powders was characterized using surface potential decay and direct charge measurements. These first set of experiments pointed out the conductive behavior of these powders: in contact with a grounded electrode, they lose their charge in less than 10s. In a second set of experiments, mixtures of 50% peeling and 50% gluten powders were processed by electrostatic separation. Experimental design methodology was used to model the outcome of the separation process as function of two control variables: the high-voltage applied to the roll electrode and the speed of the belt conveyor electrode. In this way, it was possible to determine the optimal operational conditions for the recovery of high-purity peeling and gluten fractions