Electrification Of Particles Research Articles

Investigation of the role of temperature on contact electrification of polyethylene particles

This work investigates the role of temperature on contact electrification of polyethylene particles. Particles were shaken at ambient temperature and 60 °C in two stainless steel cups with one having its wall coated with polyethylene particles. Particles in contact with a bare wall did not show a variation in charge transfer when temperature increased; however, contacts with an insulating coated wall resulted in a lower charge generation. A volume resistivity cell was designed and built to measure changes in volume resistivity with temperatures. Although reliable data for particles was not obtained, but volume resistivity of different insulating films declined at 60 °C. It was concluded that this drop could increase the mobility of charge carriers and facilitate the electrostatic charge dissipation between particles or to the ground, resulting a lower charge build-up on particles. This work recommends investigating the role of temperature when ion and material transfer mechanisms are at play.

Effects of Electrification and Transverse Force on Dusty Flow over a Linear Stretching Sheet

The numerical investigation of the flow and heat transfer of steady dusty flow over a linear stretching sheet has been carried out. The effects of Transverse force and electrification has been incorporated in this problem. Modelling of the problem comprises of highly nonlinear partial differential equations that have been transferred to systems of ordinary differential equations by implementing suitable transformations. Since the equations are of boundary value problems in nature, have been transferred to initial value problem by using shooting method and then solved by RungeKutta 4th order technique. All the above numerical methods incorporated in the BVP4C tool of MATLAB and has been solved the systems of differential equations by using MATLAB software. The effects of different parameter like Prandtl number, Eckert number, transverse force, and electrification parameter on flow and heat transfer profile has been presented through graphs and tables. The results have been validated with previous authors. From the graph it is observed that the transverse force reduces the velocity of the particle phase in the flow where as electrification of particles raises the temperature of particle phase in the flow. The computations carried out with tolerance of order less than O (10^(-6) ).

Flow And Heat Transfer of Unsteady Two-Phase Boundary Layer Flow Past an Inclined Permeable Stretching Sheet with Electrification of Particles

In the present study, an analysis has been carried out for a particle laden boundary layer flow with existence of electrification of particles has been studied over an inclined permeable stretching sheet. In most of the MHD fluid flow problems, either the plate is externally supplied by the magnetic/electric field or the fluid is electrically conducting. In the present problem, neither the plate is electrified nor the fluid is electrically conducted, but due to the random motion of the particles, collision of particle-particle and particle–wall, the particles are electrified. This electric field affects the fluid flow and heat transfer of the flow problem. Again, in the previous literatures, Buoyancy force is considered in momentum equations of fluid phase only. But in reality, both the phases are affected by the buoyancy force. For this reason, a reasonable mathematical model for two-phase buoyancy driven flow has been formulated with the consideration of electrification of particles in both fluid and particle phase. The governing system of PDEs are transferred to system of ODEs by applying similarity transformations and then computed by implementing Runga-Kutta method. The impact of electrification and other fluid parameters on flow and heat transfer has been studied. The results are represented through graphs and tables

Numerical investigation of powder dispersion mechanisms in Turbuhaler and the contact electrification effect

Powder dispersion in dry powder inhalers (DPI) is affected by factors such as device design and flow rate, but also electrification due to particle–particle/device collisions. This work presented a CFD-DEM study of powder dispersion in Turbuhaler®, aiming to understand the effect of electrostatic charge on the dispersion mechanisms. The device geometry was reconstructed from CT-scan images of commercial Turbuhaler device. Different work functions were applied to the active pharmaceutical ingredient (API) powder and the device wall. Electrostatic charges were accumulated on the API particles due to contact potential difference (CPD) between the particles and the device wall. Results showed that both the chamber and the spiral mouthpiece played an important role in de-agglomeration of powders caused by particle–wall impactions. With increasing flow rates, the performance of the device was improved with higher emitted dose (ED) and fine particle fractions (FPF). The electrostatic charging of the particles was enhanced with higher CPD and higher flow rates, but the electrostatic charging had a minimum effect on powder dispersion and deposition with slight reduction in ED and FPF. In conclusion, the van der Waals force is still the dominant adhesive inter-particle force, and the dispersion efficiency is affected by the flow rate rather than contact electrification of particles. Future work should focus on the effect of highly charged particles emitted from the inhaler on the deposition in the airway.

Mechanism of Electric Charging of Aluminum Oxide Particles When Burning Solid Fuels

The mechanism of electrical charging of particles of aluminum oxide during the combustion of aluminized solid fuels due to the capture of ions and electrons by particles in high-temperature combustion products is considered. An analysis of the kinetics of aluminum oxide primary particles charging in the combustion zone around an aluminum particle was performed. It is shown that the charging of primary oxide particles via the capture of ions and electrons is fast. Moreover, because of the higher mobility of electrons, the particles are charged predominantly negatively. Thermionic emission is considered as an additional mechanism for the electrification of aluminum oxide particles. Because of the lack of data on the work function of the molten aluminum oxide, the parametric calculations for the primary particles electrification were performed at different values of the work function. Based on the experimental results for the electrification of oxide particles in the combustion products of aluminized solid fuels, the work function of electrons, for which the charge distribution of primary oxide particles is close to bipolar, is estimated.

Venus lightning: Estimation of charge and dimensions of charge regions for lightning initiation

The occurrence of Venusian lightning must be preceded by electrification of particles in Venusian clouds and separation of these charged particles to form distinct charged regions. In this work, we estimate the minimum required charge and the dimensions of these charge regions in order for lightning to occur. The expected streamer speed in Venusian middle clouds is on the order of 105–106 m/s. The charged region in Venus's middle clouds has been approximated as uniformly charged cylinders. The radius, thickness, and charge density of the charged region have been estimated to be about 1–20 km, 1–3 km, and 1–28 nC/m3, respectively. The lack of global magnetic fields on Venus has resulted in the formation of weak induced magnetic fields that give unrestricted access to Galactic Cosmic Rays (GCR). The ionization of the lower atmosphere of Venus due to GCR has been a subject of many earlier studies, and it has been considered a source for cloud electrification on Venus. The fields produced by charged regions with charge density levels from GCR-induced ionization do not exceed breakdown fields. The required levels of charge density could be produced by collisional charging.

Velocity Profile of Fluid Particle Suspension over a Horizontal Plate with Electrification of Particles

The modelling of electrified flow over a horizontal plate is considered. Here the fluid is of Newtonian type and fluid-fluid, fluid- particles collisions are accounted. The effective volumetric force, viscous dissipation, browanion diffusion, in fluid phase as well as particle phase has been considered. In this paper we considered the generation of electricity due to hitting of particles with each other and with the wall of the flow and its impact on motion of flow particles. The systems of equations representing the flow are solved by finite difference method. It concludes from outcome of computation that the particle velocity rises with rise of electricity generation and increasing size of particles.

Quantitative analysis of agglomerates levitated from particle layers in a strong electric field

The electrification, agglomeration, and levitation of particles in a strong electric field were analyzed experimentally and theoretically. Particle layers of glass, alumina, and ferrite were formed on a plate electrode and an external voltage was applied. Microscopic observations of the agglomerates levitated from the particle layers revealed that the number of primary particles constituting an agglomerate is affected by particle diameter and electrical resistance, but not by the applied electric field. The electric field distributions in the system were calculated by considering the charges and geometries of the agglomerates formed on the particle layers. The charges of the agglomerates were obtained experimentally. All forces acting on the agglomerates (i.e., gravitational forces, Coulomb forces, interaction forces between polarized particles, image forces, and gradient forces) were analyzed under different conditions, including various electric field distributions and charges of agglomerates. Furthermore, the critical conditions for the levitation of the agglomerates were evaluated using a force balance.

Electrostatic Charge Generation in Pneumatic Conveying Process: Effect of Particle Properties

One of the main concerns in particle pneumatic conveying process is the possibility of hazards for operation safety due to the electrostatic charge generation as a result of collisions between particles and the equipment wall. Indeed, the electrostatic discharge can occur in the equipment leading to fire or explosion. Simulation of these kinds of processes plays an important role in understanding the various aspects of the system in order to production loss prevention. This paper deals with the simulation of particle pneumatic conveying process inside an inclined tube using a particular method. In this method, the electrification of particles inside the tube is influenced by the vertical collision velocity against the tube wall. Simulation of the particle movements inside the tube, generation of electrostatic charges over the particle surfaces as well as the possibility of fire as a result of discharging the electrostatic energy are investigated. The possibility of fire is investigated by comparing the amount of electrostatic energy with minimum ignition energy (MIE) of the particles. The effect of particle properties including the size and mechanical ones in the simulation is studied. Finally, several solutions are proposed to manage the risk of fire and explosion. As results, the electrostatic energy (E) is beyond the MIE, and the electrostatic discharge can occur leading to explosion for the diameters more than 2 mm and also for elasticity constants lower than 140 MPa. Eventually, there is no hazard of fire and explosion, since all calculated electrostatic energy for the change of Particle Poisson’s ratio varying from 0.1 to 0.9 is less than the MIE value for the air flow rate of 10 m3/h.

Particle electrification and levitation in a continuous particle feed and dispersion system with vibration and external electric fields

Electrification and levitation of particles in a continuous particle feed and dispersion system have been studied both theoretically and experimentally. This system consisted of a vibrator and inclined parallel electrodes. A mesh and a vibrating plate were used for the upper and lower electrodes, respectively. A dc voltage was applied to one of the electrodes and the other electrode was grounded. Particles fed to the lower electrode were charged by induction and levitated upward by the Coulomb forces. When the applied voltage was high enough, the particles passed through the mesh electrode. The charge of the particles was measured with a Faraday cup, and the particle behavior was observed with a high-speed microscope camera. The particle charges were also analyzed from experimentally obtained particle trajectories and numerically calculated electric fields. Finally, the conditions for the effective levitation and dispersion of the charged particles and their mechanisms were studied and have been described in detail.

АНАЛІЗ ЧАСОВОГО РОЗПОДІЛУ КІЛЬКОСТІ ВИПАДКІВ ГРОЗ НА АЕРОДРОМІ ОДЕСА

Thunderstorm is an atmospheric phenomenon that manifests itself in the form of electrical discharges in cumulonimbus clouds of lightning. Usually, lightning arise between the surfaces of the earth and the clouds. Sometimes electric flashes can go inside the cloud. At the same time on Earth there are about one and a half thousand thunderstorms, the average intensity of discharges is estimated at 46 zips per second. On the surface of the planet thunderstorms are distributed unevenly. Above the ocean thunderstorm is observed about ten times less than over continents. In the tropical and subtropical zone, about 78% of all bursts of lightning are concentrated. The maximum thunderstorm activity is in Central Africa. The intensity of thunderstorms follows the sun: the maximum of thunderstorms is observed in the summer (in medium latitudes) and in the afternoon. The minimum of registered thunderstorms falls on time before sunrise. Storm in Ukraine is constantly happening even in the winter months. They are especially dangerous in the steppe zone, the strikes of lightning strike all that, at least slightly rising above the grass or shrub. Lightning - an electrical discharge between the clouds or between the cloud and the earth. Inthe process of formation of rainfall in the cloud, the electrification of droplets or ice particles occurs. As a result of strong upward flow of air in the cloud, separate regions are formed, charged with different charges. When the intensity of the electric field in the cloud or between the lower charged region and the ground reaches a breakdown value, lightning arises. In such a weather, there are stormy clouds. As a rule, this event is accompanied by thunder, shower, hail and strong wind. The high density of settlements and agro-industrial facilities in the south of Ukraine, the intensity of air transportation at the international airport of Odessa and the construction of high-rise buildings require increased attention to prevent the devastating effects of natural hydrometeorological phenomena. One of the most dangerous HMAs for a society's life is a variety of convective phenomena, that is, showers, thunderstorms, hailstones, squalls, and tornadoes. They significantly affect the life, health and economic activity of man. For example, the defeat of people, aircraft with lightning, radio interference, interruptions in electrical supply - this is not a complete list of negative factors associated with thunderstorms. The purpose of the work was to study lightning activity at the Odessa airfield for 2013-2017 years. Daily observation of atmospheric phenomena was used as the source data for the study.

The role of fluid turbulence on contact electrification of suspended particles

A probabilistic version of a well-known phenomenological model for contact electrification is used to examine the effect of fluid turbulence on charge development for suspended particles as a function of the particle Stokes number. The distribution of particle collisions and particle charge appear to approach asymptotic states for high values of the Kolmogorov-scale Stokes numbers, exhibiting approximately normal distributions. The influence on particle contact electrification of differences in initial charge carrier density and in particle size are examined.

Direct numerical simulation of triboelectric charging in particle-laden turbulent channel flows

The electrification of particles embedded in a turbulent flow may cause hazards such as spark discharges but is also exploited in several industrial applications. Nonetheless, due to its complexity and sensitivity to the initial conditions, the process of build-up of particle charge is currently not well understood. In order to gain a deeper understanding of this phenomenon, we performed fully resolved numerical simulations of particle charging. More specifically, our study concerned the charging process of particles dispersed in a turbulent channel flow at a friction Reynolds number of $Re_{\unicode[STIX]{x1D70F}}=180$. Emphasis was placed on the analysis of the interplay between the different physical mechanisms underlying particle electrification, such as fluid turbulence, particle dynamics and particle collisions. Further, we investigated the influence of some important physical parameters. According to our simulations the charge build-up depends strongly on the particle Stokes number, $Stk$. In particular, at small Stokes numbers, $Stk=0.2$, the turbopheretic drift inhibits particle charging. By contrast, at moderate Stokes numbers, $Stk=2$, and low particle number densities, the electric charge builds up but cannot escape the viscous sublayer due to limited particle migration. However, in the case of high particle number densities, the charge is transported away from the wall via inter-particle charge diffusion. A further increase to $Stk=20$ leads to strong charging and particle-bound charge transport towards the bulk of the channel.

Effects of moisture content on electrostatic sensing based mass flow measurement of pneumatically conveyed particles

Mass flow rate measurement of pneumatically conveyed particles is desirable for the optimal control of many industrial processes. The unpredicted variation of moisture content in particles affects the accuracy of mass flow measurement of particles in enclosed pipelines using electrostatic electrodes. In this study, the characteristics of measured electrostatic signals from particle flow under different flow conditions are analysed to study the effect of moisture content on the mass flow rate measurement. The measurement principle of ring-shaped electrostatic electrodes, the effects of moisture content on electrification of solid particles, and the experimental setup used in the study are presented. Two types of electrostatic electrodes with different axial widths and structure are adopted to measure the electrostatic signals of nonporous glass beads and porous activated carbon powder on the vertical pipeline of a 74mm bore gas–solid two-phase flow test rig under various moisture content, mass flow rate and conveying velocity conditions. The experimental results indicate that the amplitude and frequency characteristics of the electrostatic signals change with the moisture content. The deviation of mass flow measurement that caused by the variation of moisture content is analysed, and a recalibration process is demonstrated to be effective for the improvement of measurement accuracy.

Effects of Electrification of Particles and Viscous Dissipation on Unsteady Two-phase Flow over a Stretching Sheet

Effects of Electrification of Particles and Viscous Dissipation on Unsteady Two-phase Flow over a Stretching Sheet

第1章 粒子の性質と測定 1.8 静電気的性質 1.8.2 液相中での帯電と計測

第1章 粒子の性質と測定 1.8 静電気的性質 1.8.2 液相中での帯電と計測

Multiparametric observation of volcanic lightning: Sakurajima Volcano, Japan

AbstractWe recorded volcanic lightning generated by Vulcanian explosions at Sakurajima Volcano using a synchronized multiparametric array. Physical properties of lightning are related to plume dynamics, and associated electromagnetic field variations are revealed by video observations (high speed and normal speed) together with infrasound and high sampling rate magnetotelluric signals. Data show that volcanic lightning at Sakurajima mainly occurs in the plume gas thrust region at a few hundred meters above the crater rim, where the overpressure of the turbulent volcanic jets determines the electrification of particles generating a complex charge structure in the growing plume. Organization of charges may be achieved at later stages when the plume transitions from the jet phase to the convective phase. Comparison with atmospheric sounding and maximum plume height data show that the effect of hydrometeors on flash generation at Sakurajima is negligible and can be more prudently considered as an additional factor contributing to the electrification of volcanic plumes.

Post-dispersion electrification of droplets

Electrification of aerosol particles dispersed by a pneumatic atomizer is presented in the paper. For post dispersion electrification of droplets a contact method with external high voltage electrode was proposed. Experiments were carried out using supersonic atomizing head, equipped with a high voltage mesh electrode, placed co-axially and perpendicularly to the droplets stream and closely to the atomizing head. Results of experimental investigations have shown, that the Q/m ratio values depends on the liquid feed rate according to the power type function. Two steps electrification model with a space charge was proposed for explanation of the observed dependence. Calculations carried out on the basis of proposed model confirmed, that the space charge component of the electric field is significant for the final Q/m ratio value, and allow to determine Q/m value with accuracy on the level of 10%. The model suggests bipolar nature of charge carried by droplets leaving the electrification system.

Electro-optical phenomena in a gas-dispersed jet flow around a solid body

In continuing studies [1–4] in which optics and electrification of particles colliding with a body around which a high-speed two-phase jet flows are considered, there was an attempt to explain the experimentally observed luminescence [5] of a conducting body, bombarded by microparticles, by the presence of a reverse unipolar current (from rebounded particles) exciting carrier-gas molecules. The process of charge acquisition by a particle in collision with a solid is complex: not only the value of the charge but even its sign are unknown in many cases [6]. A simple model is proposed for estimating the characteristic values of the reverse current density and the spatial distribution of the gas luminescence energy.

Numerical analysis of contact electrification of non-spherical particles in a rotating drum

Contact electrification is generally referred to as the charge transfer process between particles during collisions. The transferred charge can be accumulated on the surface of the particles especially for insulating materials with irregular shapes, which can lead to a non-uniform charge distribution and eventually affects the charge accumulation process. In this study, in order to investigate the influence of the particle shape on contact electrification, a sphere-tree multi-sphere method and a contact electrification model are implemented into the discrete element method (DEM) to model the charging process of irregular particles in a rotating drum. Irregular particles with various Sauter mean diameters but the same maximum diameter and equivalent volume diameters are considered. The charge distribution and accumulation on the particles are investigated. It is found that the charge transfer originates from the contact between the particle and the drum due to the contact potential difference and initially takes place primarily at the region near the wall of the drum. The charge eventually propagates to the entire granular bed. The charge of the particles increases exponentially to an equilibrium value. For particles with the same maximum diameter, a larger charging coefficient is obtained for the particles with smaller Sauter mean diameters and sphericities, which leads to a faster charge accumulation, while for particles with the same equivalent volume diameter and fill ratio, similar charging coefficients are observed. A non-uniform intra-particle charge distribution is induced on each individual multi-sphere particle.