Contact electrification and charge distribution on elongated particles in a vibrating container (original) (raw)
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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.
Advanced Powder Technology, 2003
In powder handling, each particle collides with another particle or a wall, and consequently becomes charged up to a certain value. Such contact charging is experienced in various elds. In the present review, the basic concepts of contact charging are summarized; in particular, the effect of the contact potential difference and the initial charge on the charge transfer is described in detail. Furthermore, the variation of the particle charging caused by repeated impacts on a wall is formulated. This theory is extended to the particle charging in gas-solids pipe ow, where each particle has a different amount of charge; the distribution of the particle charge is also analyzed theoretically. In addition, the method of measuring important electrostatic properties, the technique of detecting particle charging and the application of particle charging are described.
Journal of Electrostatics, 2013
The triboelectric charging of granular insulating materials is very difficult to predict because of the complex physical mechanism involved in this process. The aim of this paper is to describe in detail the implementation of a numerical model of the tribocharging process taking place in vertically-vibrated beds of granular plastics. The charge exchanged in granule-to-granule and granule-to-wall collisions is computed by taking into account some electrical properties of the respective materials, their area of contact and the effect of the electric field generated by a system of high-voltage electrodes and by the charges of the granules themselves. The electrical model is coupled with the Discrete Element Method (DEM) which undertakes the whole granular dynamics and allows to compute accurately the contact surface of two colliding particles which is involved in the triboelectric charging model. Beside the numerical simulations an experiment has been conducted with mixtures of mm-size polyamide and polycarbonate granules in a laboratory vibrated bed to validate the model. The numerical results have been found to be in good agreement with the experimental ones.
Characterization of Particle Electrostatic Charging in Vibration and Electric Field
A novel system for characterizing particle charging as a function of the distance traveled has been designed and manufactured on the basis of the particle charging induced by repeated contacts with a wall. A vibration of several hundred hertz is applied for effective contact of the particles with the wall. In addition, an electric field is applied to change and control the charge on the particles. Using this system, sample particles with diameters of less than a hundred micrometers are studied under varying conditions of particle material and electric field strength. It is verified that the particles repeatedly contact the wall through the observation of the behavior of the particles on the vibrating wall using a high-speed camera with a zoom lens. Furthermore, it is confirmed that the system has an excellent performance to characterize particle charging from the theoretical and experimental analyses of the particle charge accumulation.
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The systematic errors due to the practical implementation of the contact dynamics method for simulation of dense granular media are examined. It is shown that, using the usual iterative solver to simulate a chain of rigid particles, effective elasticity and sound propagation with a finite velocity occur. The characteristics of these phenomena are investigated analytically and numerically in order to assess the limits of applicability of this simulation method and to compare it with soft particle molecular dynamics.
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Electrostatic forces cause spontaneous movement of charged particles; subsequently, electrostatic technology is attracting attention because of its application in powder handling processes, such as separation, classification, dispersion, and collection. Dielectric and conductive particles are charged by induction in a strong electric field and moved by Coulomb forces. The magnitude and polarity of the transferred charges are controlled by the strength and direction of the electric field. The dielectric particles are also polarized in the electric field, and dipole interactions occur between particles or in the particle layers, complicating the particle behavior. This review paper presents induction charging, agglomeration, levitation, and other behaviors resulting from particle layers in electric fields. A series of particle phenomena occur in parallel electrode systems, which consist of a lower plate electrode and an upper mesh electrode. Charged agglomerates are formed on the particle layers, levitated by the Coulomb forces, and disintegrated with rotation when approaching the mesh electrode. The mechanisms of agglomeration and disintegration have been elucidated in multiple studies, including microscopic observations and theoretical analyses of particle motion, based on numerical calculations of the electric field. Furthermore, a new system is proposed for continuous feeding of dispersed particles using electric fields and vibration.
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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.