Neutralisation of electrically-charged insulating granular materials (original) (raw)
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IEEE Transactions on Industry Applications, 2013
Neutralization of the residual electric charge is often a prerequisite for the optimal processing of insulating granules, thin films, or textile media. The aim of this paper is to evaluate the factors that might affect the ability of ac corona discharge to eliminate the charge at the surface of polyethylene granular materials. The effectiveness of the neutralization is evaluated from the measurement of surface potential distribution before and after exposing the samples to a flux of bipolar ions. The corona discharge was generated by energizing at various high-voltage (HV) levels (16, 20, and 25 kV) and frequencies (1, 20, 50, 100, 200, and 400 Hz) a wire-type corona electrode suspended at 30 mm above the granular layer disposed at the surface of a grounded plate. The results show that the neutralization efficiency can be improved by increasing the frequency of the HV. An optimal value voltage can be experimentally determined for the case of practical interest when the frequency of the power supply is 50 Hz. In the same case, successive exposures to the ac corona discharge may enhance the efficiency of the neutralization.
Neutralization of charged insulating granular materials using AC corona discharge
Journal of Electrostatics, 2011
The control of the residual electric charge carried by granular materials processed in various electrostatic installations is a prerequisite for the safe and efficient operation of the respective industrial equipment. The aim of the present work was to evaluate the neutralization efficiency of polyethylene granules exposed to an AC corona discharge from a wire-type electrode. The control variables and their domains of variations were the following: the amplitude and the frequency of the applied high voltage (16e18 kV, 20e400 Hz), the position of the corona electrode (3e7 cm above the ground plate that carries the sample) and the duration of the exposure to the corona discharge (4e10 s). The surface potential decay method was used for monitoring the charge carried by granular samples of PE before and after neutralization. Design of experiment methodology was employed to evaluate the influence of each of the above mentioned control variables and determine the optimum operation conditions. The efficiency of the neutralization was characterized by the ratio between the values of the surface potential before and after AC corona discharge exposure. The obtained results show that neutralization efficiency may be improved by increasing the frequency of the high voltage as well as by adequately correlating its amplitude with the inter-electrode spacing.
Journal of Electrostatics, 2011
Surface potential decay method has been frequently used to characterize the charge state of insulating materials. The present paper aims at a critical evaluation of this method when used for the characterization of granular plastics, by comparing it with the electric field monitoring by means of non-contact vibrating probes, and with the measurement of the charge induced in a capacitive probe connected to a Coulomb-meter. The experiments were performed on corona-charged polyethylene, polycarbonate, polyamide, and acetyl e butadiene e styrene granular materials. The experimental results show that surface potential decays faster than the electric field or the charge measured with the capacitive probe. The dimensions of the probes and the capacitive coupling between them and the samples, may explain this difference. Part of the potential decay measured by the smaller-size probe of the electrostatic voltmeter is due to the surface conduction, while the measurements made with the larger-size electric field and capacitive probes are less affected by this phenomenon.
Properties of electrostatically-driven granular medium: Phase transitions and charge transfer
AIP Conference Proceedings
The experimental and theoretical study of electrostatically driven granular material are reported. It is shown that the charged granular medium undergoes a hysteretic first order phase transition from the immobile condensed state (granular solid) to a fluidized dilated state (granular gas) with a changing applied electric field. In addition a spontaneous precipitation of dense clusters from the gas phase and subsequent coarsening -coagulation of these clusters is observed. Molecular dynamics simulations shows qualitative agreement with experimental results.
Corona charging of granular layers of insulating particles at the surface of a grounded electrode
Journal of Electrostatics, 2005
The aim of the present paper is to introduce a simple experimental technique for estimating the corona charging conditions of insulating granules that form a layer at the surface of the grounded electrode of roll-type electrostatic separators. The basic idea consists in measuring the potential at any point on the surface of this layer by means of an electrostatic probe. The capacity of the probe-layer system being constant, the measured potential is proportional to the charge. The results clearly show that the charges imparted to the particles in the corona discharge depend on their positions at the surface of the electrode and on the inter-electrode spacing. This observation could be of use, for instance, to particle charging simulations performed as a preliminary step of any feasibility study of new electrostatic separation applications. r
Experimental Modeling of the Electrostatic Separation of Granular Materials
Particulate Science and Technology, 2007
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Journal of Electrostatics, 2017
The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect.
The effect of vibrating conditions on the electrostatic charge in a vertical vibrating granular bed
Powder Technology, 2011
In this study, we carried out experiments to measure the electrostatic charge of a granular matter in a vertical shaker device. The purpose was to quantify the effect of the vibrating conditions on electrostatic charging in the granular matter. In each experimental run, 3 mm glass beads were first discharged to remove any residual charge prior to subsequently studying their electrostatic charging. The accumulative electrostatic charges of the granular materials were measured using a Faraday cage. The findings show that the vibrating conditions play an important role in the saturated electrostatic charge and time constant. The electrostatic charges of granular materials are mainly generated by the contact potential difference mechanism in the vibrating granular system. The results show that the saturated accumulation charge increases as the dimensionless vibrating acceleration increases, and decreases with increasing vibrating frequency. The time constant is small when a higher vibrating frequency is applied in the vibrating granular system. Finally, we demonstrate that the saturated accumulation charge increases linearly with the increase of the dimensionless vibrating velocity regardless of the vibrating frequency.
Journal of Physics: Conference Series
Dielectric barrier discharge (DBD) is a promising technology for surface modification of materials. In recent investigations; researchers have found that DBD plasma exposure changes the triboelectric properties of insulating materials. The aim of the present study is to evaluate the effect of three major operating parameters of the DBD reactor on the triboelectric charging of plasma-exposed granular materials. The factors considered in this study were: the distance between the two electrodes of the plasma reactor, the thickness of the dielectric and its position. The plasma treated Polyethylene (PE) particles were then tribocharged in a vibrating device; the acquired charge was measured using a Faraday pail connected to an electrometer. Results show that both the distance between the electrodes and the thickness of the dielectric barrier have a considerable effect on the tribocharge acquired after DBD treatment. Conversely, for fixed gap spacing, the dielectric barrier configuration does not have a significant effect on charge enhancement.
Powder Technology, 2010
Electrostatic forces can significantly alter flow properties of granular materials and can adversely affect many industrial particulate processes in unpredictable ways. We investigate here the effect of higher order dielectric electrostatic forces, which are created by non-uniform electric fields, on the agglomeration, adhesion and flow of several granular materials, including pharmaceutical powders. We find that materials can adhere consistently and reproducibly to a metallic rod in a sufficiently strong electric field, which can be produced by either a DC source or tribocharged surfaces. These results provide a simple way to characterize material susceptibility to electrostatic agglomeration. The effect of applied non-uniform fields on the flow of grains falling from a cylindrical hopper is studied and found to significantly reduce the particle flow rate. The effects of humidity, particle size, coatings, and the grounding of equipment are also tested. Finally, contrary to common intuition, we find that grounding a metallic surface can actually exacerbate particle adhesion and agglomeration.