Electrodynamics of a convective cloud

An attempt has been made to describe analytically the electrodynamics of a convective cloud on the basis of a one-dimensional convective cell with solid gas rotation. The cloud electrification is due to the interaction between heavy (large raindrops and particles of hail) and light (microparticles of water and ice) particles. As a result, the particles acquire unlike electric charges. The large-scale electric field in the cloud is stipulated by boundary effects and influences considerably the motion of the heavy fraction of aerosol particles. A scenario is proposed for the development of an intracloud charge, by which the large-scale electric field does not reach the breakdown value, staying at the level of the corona discharge field, while an increase in the irregular component of the electric field is continued and achieves the breakdown value in the small-scale electric cells induced by analogues of plasma beam instabilities. The basic electric discharge occurs against the background of multiple discharges inside the cell which provide for the leader lightning channel. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, Nos. 1–2, pp. 123–137, January–February, 1997.     

Forced corona method for the evaluation of fabrics with conductive fibres

Modern fabrics for protective clothing, used in environment where the level of static charge must be controlled, are composites where a grid or stripes of conductive fibres are present inside a matrix of highly resistive base fabric. In protective clothing, where the conductive fabric elements are not effectively grounded, corona discharge is the major limiting mechanism for fabric charging. In this paper, corona discharge of electrostatic discharge protective fabrics has been studied. A new experimental method, forced corona, was developed for the measurement of corona onset and offset potentials as well as corona current. According to results, the residual level of fabric surface potential after corona discharge was the lowest in fabrics containing core conductive fibres. The behaviour is because of the small dimensions and sharp edges of the core conductive fibres.     

Effect of spark discharges on the trajectories of insulating particles in roll-type corona-electrostatic separators. Experimental and numerical study

Corona-electrostatic separation is a multi-variable process that has been thoroughly studied in connection with its various applications in the recycling industry. The aim of the present paper is to point out one parasitic phenomenon that adversely affects the efficiency of the separation: the sparks generated at the passage of conductive particles through the electric field zone. The experiments were carried out on a laboratory roll-type corona electrostatic separators, and the sparks were generated by introducing 16 calibrated copper pins in 40-g samples of granular insulating material (PVC; typical granule size: 1.5 mm) that were fed at a constant rate onto the surface of the grounded rotating roll electrode. The distribution of the PVC granules in the 14 boxes of the collector was altered by the occurrence of the spark discharges, as they were accompanied by the annealing of the electric field between the electrodes. The numerical simulation of insulating granules charging and movement under the action of the electric field enabled a better understanding of the interactions between the spark discharges and the other factors that influence their trajectories and affect the efficiency of the separation: roll-speed, particle size and ambient humidity. The particle dynamics equations were solved using an iterative scheme by using the electric field calculated in any point with the commercial software TRICOMP. The good agreement between the predictions made by these simulations and the experimental findings confirms the ability of the mathematical model to reflect the complexity of the physical phenomena.     

Comparative study of three high-voltage electrode configurations for the electrostatic separation of aluminum,copper and PVC from granular WEEE

Roll-type electrostatic separators are mostly employed for the selective sorting of conductive and non-conductive constituents of granular mixtures. In case of waste electric and electronic equipment, several conductive materials may be simultaneously present in the composition of the granular mixture to be separated. The aim of this paper is to prove the feasibility of processing an Aluminum/Copper/PVC mixture using a roll-type electrostatic separator. Three high-voltage electrode configurations were studied. Experiments prove that the association of a high-voltage S-shaped plate electrode with a corona wire electrode gives the best separation results. The electric forces pin the corona-charged PVC particles to the roll electrode, while the lighter aluminum and heavier copper particles are diverted to the high-voltage electrode. The aluminum contained in the copper product can be removed by a second pass in a separator that makes use only of the S-shaped electrode. In this way, 75% of the aluminum particles and 99.97% of the PVC particles can be removed, to obtain a 98% pure copper product.     

Effect of relative humidity on current–voltage characteristics of monopolar DC wire-to-plane system

This paper deals with the DC monopolar corona discharge in wire-to-plane geometry under variable humid air conditions. The classical formulas of Townsend commonly used for the current–voltage characteristics were used to determine the various corona parameters for the both polarities of the corona discharge. A circular biased probe has been adapted to the plane and is used to measure the ground plane current density and electric field during the monopolar corona discharge. A new approach to the problem of corona discharge in transmission system has been described in this paper. The effect of varying the humidity and wires diameter is also investigated. The values of the electric field and the current density are maximum beneath the corona wire and decrease when moving away from them and the current–voltage characteristics follow the quadratic Townsend's law. The experimental results show that the monopolar corona discharge is strongly affected by the air humidity. The current density and the electric field are measured and compared with the computed values. The agreement between the calculated values and those obtained experimentally is satisfactory. The per unit electric field and current density are also represented by a unique function.     

Modelling of ions for seeding technique to electrify the atmosphere

There are number of ways in which weak electrification can affect the microphysics of clouds, with consequences for cloud lifetime, radiative properties, and precipitation efficiency. Kauffman [2011] suggested ions produced by direct current generators will add to and enhance the catalysing effects that cosmic ray ions are now known to produce in among other things, lowering nucleation barriers, stimulating charged particle growth and stability and increasing the scavenging rate in clouds. Thus to electrify the atmosphere ions can be generated artificially in abundance along with large electric field.Ions can be generated by the corona effect using Atmospheric electrifiers (a device used to generate negative ions) which makes use of corona discharge phenomenon to charge the air particles. Exact assessment of electric field and charge density distributions and the flow dynamics inside the electrifiers is essential to understand the particle behaviour inside the electrifiers.In this paper, a novel model of governing equations to evaluate the space charge density, electric field intensity and velocity of ionized airflow is suggested as a function of applied voltage. The Poisson and charge conservation equations are derived and hence can be used to estimate the electric field and charge density distributions. Navier stokes equation can be used to get the velocity of ionized airflow because of electric force on the air. Simulation is carried out to validate the proposed model and verify that velocity is function of input voltage and is proportional to it.     

Influence of the corona-wire diameter and length on corona discharge characteristics of a cylindrical tri-axial charger

In this paper, the corona discharge characterization in terms of current–voltage relationships of a unipolar cylindrical tri-axial charger on the effects of the corona wire diameter and length have been experimentally studied and discussed. A commercial computational fluid dynamics software package, COMSOL Multiphysics™, was used to predict the electric field distribution in the ion generation and charging zones of the charger and the ion penetration through the perforated screen opening on the inner electrode of the charger. It was found from experimental results that both positive and negative charging currents in the charging zone of the charger increased with increasing corona and ion-driving voltages. At the same corona and ion-driving voltages, both positive and negative coronas were decreased with increasing diameter of the corona-wire. Compared with the corona-wire of 22 mm in length, the magnitude of both positive and negative charging currents were markedly higher for corona-wire of 11 mm in length at the same corona voltage. It was found that the charging currents for negative coronas were about 1.2 times higher than those positive coronas at the same corona and ion-driving voltages. Numerical results of the electric field distribution and the ion and charged particles migrations in the discharge and charging zones of the charger is correlated to have the same direction with the experimental results of the current–voltage relationships. Also, this can be used to guidance in describing the electric field distribution and the behavior of ion and charged particle trajectories that cannot be seen from experiments in order to improve the applicably design and refinement of a unipolar cylindrical tri-axial charger.     

Effect of air flow on corona discharge in wire-to-plate electrostatic precipitator

This paper analyses corona discharge in ambient air with laboratory-scaled wire-to-plate electrostatic precipitator (WPESP). The electric field is behind the electro hydrodynamic (EHD) flow in air. Its measurements provide complementary results for the corona discharge study because the classical theory based on the current and voltage data is unsatisfactory. Taking into account the dynamic air flow velocity is perpendicular to the active wires, measurement method of the positive and negative DC corona current density and electric field, has been introduced. It has been shown also that the dynamic air flow velocity modifies the current density and the electric field distributions on the planes surfaces of the WPESP.     

大气压下电晕电离层离子运动规律的实验研究

对大气压下电晕电离层的离子运动规律进行了实验研究。实验结果表明: 在电晕放电的流光或辉光放电区域, 电离电场强度、注入功率密度、电离能密度等参量对等离子体输运项的影响程度仅在1 个数量级内; 在电离能密度达到0. 4mJ•cm^{- 3} , 气体速度从1. 5m•s^{- 1} 提高到25m•s^{- 1} 时, 离子输运率相应从5. 4× 10⁸ cm^{- 3}•s^{- 1} 增加到8×10¹⁰ cm^{- 3}•s^{- 1} , 提高了近2 个数量级。带电粒子的动量对离子浓度及输运的影响远大于电离电场强度、注入功率密度等的影响。     

Dielectrophoretic motions of a pair of particles in the vicinity of a planar wall under a direct-current electric field

This paper presents direct simulations on the two-dimensional dielectrophoretic (DEP) motion of a pair of particles in a viscous fluid, interacting with a nearby planar wall, to further understand the DEP interaction among multiple particles and a wall. Results show that, under an external direct-current electric field parallel to the wall-fluid interface, the nearby wall has significant effects on the DEP motion of both particles including their revolution, alignment and aligned movement. Regardless of their particle conductivity, the wall being less (more) conductive than the fluid pushes (draws) both particles to move away from (toward) it.     

The study of the ionic wind blower with multi-needles/ring type electrodes disposed on inner wall of the cylindrical blower

Corona discharge is one of many methods that convert electrical power into mechanical force. It has been studied for various industrial fields because of its many advantages over conventional motor, such as its no moving parts, simpler structure, minimizing size and so on. In this paper, a discharge system with multiple corona electrodes disposed in a ring format, is studied by focusing on the electrical and mechanical characteristics. Effective ionic wind generation is due to the corona discharge which depends on electric field. Therefore, the electric field is affected by the voltage, discharge spacing, and distance between each corona electrodes.     

3-D numerical analysis of EHD turbulent flow and mono-disperse charged particle transport and collection in a wire-plate ESP

The present study attempts to develop a detailed numerical approach and a simulation procedure to predict the motion of gas, ions and particles inside a simple parallel plate channel containing a single corona wire. A hybrid Finite Element (FEM)-Flux Corrected Transport (FCT)-Finite Volume (FVM) method is used: the FEM–FCT numerical algorithm is applied for modeling the steady-state corona discharge, while the turbulent gas flow and the particle motion under electrostatic forces are modeled using the commercial CFD code FLUENT. Calculations for the gas flow are carried out by solving the Reynolds-averaged Navier–Stokes equations and turbulence is modeled using the k–? turbulence model. An additional source term is added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations using User-Defined Functions (UDFs). The particle phase is simulated based on the Lagrangian approach, where a large number of particles is traced with their motion affected by the gas flow and electrostatic forces using the Discrete Phase Model (DPM) in FLUENT. The developed model is useful to gain insight into the particle collection phenomena that take place inside an ESP.     

Nanoparticle electrostatic loss within corona needle charger during particle-charging process

A numerical investigation has been carried out to examine the electrostatic loss of nanoparticles in a corona needle charger. Two-dimensional flow field, electric field, particle charge, and particle trajectory were simulated to obtain the electrostatic deposition loss at different conditions. Simulation of particle trajectories shows that the number of charges per particle during the charging process depends on the particle diameter, radial position from the symmetry axis, applied voltage, Reynolds number, and axial distance along the charger. The numerical results of nanoparticle electrostatic loss agreed fairly well with available experimental data. The results reveal that the electrostatic loss of nanoparticles increases with increasing applied voltage and electrical mobility of particles; and with decreasing particle diameter and Reynolds number. A regression equation closely fitted the obtained numerical results for different conditions. The equation is useful for directly calculating the electrostatic loss of nanoparticles in the corona needle charger during particle-charging process.     

The correlation between corona current distribution and collection of fine particles in a laboratory-scale electrostatic precipitator

An analysis of the electrostatic gas cleaning fundamental phenomenon shows an essential influence of discharge electrode construction on the gas cleaning process efficiency.In the physical model tests there were used rigid discharge electrodes with corona emitting elements of various geometries. Different constructions of discharge electrode were tested in the aspect of discharge current uniform distribution on collecting electrode surfaces. Measurements of discharge current distribution has been carried out for discharge electrodes with different spike shapes and in different electric field geometry. The research aim was to determine the optimal discharge electrode construction ensuring high collection efficiency of fine particles. Collection efficiency measurements of selected fly ash samples (from coal fired boilers) were carried out on a laboratory testing bench in a horizontal electrostatic precipitator model.     

TiO2包覆石墨颗粒/硅油电流变液的研究

理论计算表明,介质包覆导体颗粒用作电流变液的分散相,可以获得高剪切应力的电流变液.采用溶胶-凝胶技术在尺度为5—10μm的石墨颗粒表面成功地包覆了TiO₂,获得了金红石相TiO₂包覆石墨的复合颗粒.配制成复合颗粒/硅油电流变液,其剪切应力与纯TiO₂/硅油电流变液相比,可提高一个数量级.当电场强度为1.7kV/mm时,复合颗粒/硅油电流变液的剪切应力可达1.25kPa,电流密度小于10μA/cm². 关键词： 电流变液 包覆 2')" href="#">TiO₂ 石墨     

Autowave Regimes of Thundercloud Electrification

We consider the evolution of the electric field and charge in a one-dimensional electrohydrodynamic (EHD) distributed-parameter system which serves as a simple model of a thundercloud. A diffusion equation for the electric field is proposed which, under reasonable assumptions on the nonlinear dependence of the dissipation current on the electric field (caused by the corona effect around aerosol particles in strong fields), has autowave solutions describing the dynamics of spatially separated electric-charge regions in the thundercloud. The nonlinear set of equations describing the electric-field dynamics in an ensemble of colliding aerosol particles and light ions is reduced to a rather simple basic model which admits solutions in the form of traveling fronts and traveling pulses. We find the asymptotic values of the velocity and thickness of the space-charge front, which are determined by the diffusion and the separation and conductivity currents. Using these values, we estimate the electrostatic-energy growth rate in a thunderstorm cell at the stage of its intensive electrification. A possibility is shown of the formation of a traveling pulse of field and conductivity in such an EHD system with allowance for inductive and noninductive mechanisms of aerosol-particle charging.     

120 kV下常压空气纳秒脉冲电晕放电特性

使用上升沿15 ns、脉宽30~40 ns的重复频率纳秒脉冲电源对120 kV下大气压空气中管-板电极结构电晕放电进行了实验研究,通过电压电流测量、放电图像拍摄和X射线探测分析了纳秒脉冲电晕放电特性。结果表明:纳秒脉冲电晕放电中存在X射线辐射,但辐射强度较弱,X射线辐射计数随着气隙距离的增大而减少,随着脉冲重复频率的增大而增多;放电空间的残余电荷加强了下一个脉冲到来时的局部电场,从而导致高重复频率下易于出现分散的电晕通道。     

Instability of equilibrium of the liquid dielectric surface and formation of regular cellular structures in the field of a corona discharge

It has been established experimentally that the equilibrium of the plane surface of transformer oil under a corona electrode (needle) becomes unstable when the critical voltage, which increases with the oil layer thickness, is attained at the corona point. When the voltage at the needle exceeds the critical value, regular static cells are formed on the oil surface with characteristic sizes decreasing upon an increase in voltage. The theoretically estimated parameters of the experiment are found to be close to the experimental data. Comparison of the parameters corresponding to the occurrence of instability in the equilibrium of the oil surface in the field of the corona discharge with the parameters of instability in the equilibrium of the charged surface of liquid helium in a uniform electric field [7] demonstrates the similarity of the effects.     

Experimental study of a modified dual-type high-voltage electrode for electrostatic separation applications

Several electrode arrangements have been proposed to enhance the efficiency of insulating materials charging by corona discharge. Recent studies pointed out that the presence of metal strips in the proximity of a dual-type high voltage electrode increases the total current measured at the surface of the collecting electrode, decreases the corona onset voltage value and enlarges the reparation of current density as well. The aim of this paper is to evaluate the benefits of using such an electrode arrangement for corona charging of non-conductive particulate materials in belt-type corona-electrostatic separators. The experimental study was carried out with samples of Aluminum and Polystyrene particles in the size class 125–250 μm. The presence of grounded strips reduces the electric wind, which is associated to corona discharge but not tolerated in such processes that involve micronized materials. At the same time, it improves the corona charging conditions of non-conductive materials and as consequence the overall efficiency of the corona-electrostatic separation process. The use of the new electrode configuration is characterized by both high recovery rates and better purities of the separated products.     

Studies of the dynamic behaviour of charged dust particles in high electric fields using laser Doppler velocimetry

As a preliminary study for the collection of dust particles in an electrostatic precipitator, laser Doppler velocimetry has been used to measure the velocity of small dust particles charged in the high electric field of a model electrostatic precipitator. A differential optical system is adopted for the velocimeter. The period-measuring system is used to analyse Doppler beat signals and to obtain velocity data from them. By means of the laser Doppler velocimeter, the dynamic behaviour of the velocity and direction of moving dust particles is fully revealed as a function of the applied electric voltage in the entire collecting space of the model electrostatic precipitator, and is shown in vectorial flow diagrams of particle velocity.