EHD flow measured by 3D PIV in a narrow electrostatic precipitator with longitudinal-to-flow wire electrode and smooth or flocking grounded plane electrode

In this work, results of three-dimensional (3D) Particle Image Velocimetry (PIV) measurements of the electrohydrodynamic (EHD) flow velocity fields in a narrow electrostatic precipitator (ESP) with a longitudinal-to-flow placed wire electrode are presented. The ESP was a narrow transparent acrylic box (90 mm×30 mm×30 mm). The electrode set consisted of a single wire discharge electrode and two plane collecting electrodes. Either two smooth stainless-steel plates or two stainless-steel plane meshes with nylon flocks were used as the collecting electrodes. The 3D PIV measurements were carried out in two parallel planes, placed longitudinally to the flow duct. The positive DC voltage of up to 9.5 kV was applied to the wire electrode through a 10 MΩ resistor. The collecting electrodes were grounded. The measurements were carried out at a primary flow velocity of 0.5 m/s. Obtained results show that the flow patterns for the smooth-plate electrodes and for the flocking plane electrodes are similar in the bulk of the flow. However, the flow velocities near the flocking plane electrodes are much lower than those near the smooth-plate electrodes. This is a beneficial phenomenon, because the lower the flow near the collecting electrodes, the lower re-entrainment of the particles deposited on the collecting electrodes occurs.     

A DC corona discharge on a flat plate to induce air movement

This paper describes a DC surface corona discharge designed to modify the airflow around a flat plate. The electrode configuration consisted of two thin copper layers placed on each side of the plate's attack edge. Discharge optical measurements with a photomultiplier tube indicated that the light emitted by the plasma is pulsating at a frequency that increases with applied voltage. Moreover, with voltage higher than a threshold value, the electric discharge changes regime with brighter pulses. This discharge also induced an “ionic wind” whose velocity was measured with a pressure sensing probe (up to 1 m/s). Experiments with the particle image velocimetry system in a subsonic wind tunnel showed that this discharge can reduce the separated airflow on the flat plate for a flow of 14 m/s (Reynolds number of 187,000).     

Electrical breakdown of the space vacuum

The insulating properties of the vacuum of space are examined in this paper. Generic electrode configurations are introduced to calculate the leakage current to the electrodes and the breakdown potential of the “space-vacuum” as a function of altitude above ground. The condition that defines the breakdown threshold is dependent on the size of the sheath, r_L-B, relative to the interelectrode separation, r_c. Results for the leakage currents and breakdown voltage are presented for both cases r_L-B>r_e and r_L-Be, and discussed in the context of space power systems and the SPEAR Program in particular     

Behaviour of charged insulating particles in contact with a rotating roll electrode

The overall economic efficiency of standard industrial roll-type separators for granular materials can be improved by operation at higher velocities of the rotating roll electrode. The aim of this paper is to estimate how high this speed could be and still have a good separation. The answer to this question implied the calculation of the electric image force, which opposes the centrifugal force and sticks the corona-charged insulating particles to the rotating roll electrode. This force depends on the residual charge carried by the particles. By estimating the decay of this charge from surface potential measurements carried out on granular layers of insulating materials dispersed on grounded plate electrodes, it was possible to simulate the particle lift-off from the rotating roll electrode under various operating conditions. The results presented in the paper were obtained for fly-ash particles, but the numerical simulation methodology employed by the authors can be successfully applied for the optimisation of other electrostatic separation applications.     

EHD flow in a wide electrode spacing spike–plate electrostatic precipitator under positive polarity

In this work, results of two- and three-dimensional particle image velocimetry (PIV) measurements of the flow velocity fields in a wide spacing spike–plate electrostatic precipitator (ESP) under positive polarity are presented. A DC voltage of positive polarity (up to 28 kV) was applied to the spike electrode. The average gas flow velocity was 0.6 m/s. The PIV measurements were carried out in four planes perpendicular to the plate electrodes. Three parallel planes passed along the ESP while one plane passed across the ESP duct. The results show that electrohydrodynamic (EHD) secondary flow with relatively strong vortices exist in the ESP. The EHD secondary flow pattern depends on applied voltage and measuring plane position in respect to the spike tip. The strongest vortices occur in the plane passing through the tip of the upstream-directed spike. These relatively strong EHD vortices may hinder collection of the particles in the diameter range of 0.1–1 μm in the wide electrode spacing spike–plate ESPs.     

Design and evaluation of a unipolar aerosol charger to generate highly charged micron-sized aerosol particles

In this study, a unipolar charger for generating highly charged microparticles was designed and its performance was evaluated both theoretically and experimentally. The measured particle charge number and corona current of the charger were in good agreement with the theoretical results from FLUENT. The experimentally determined average particle charge number of 1 μm PSL under an applied voltage of 8 kV was 128, which agreed well with the theoretically predicted and simulated values of 118 and 121, respectively. Computational calculations revealed the average charge of 10 μm particles to be 7560 at an applied voltage of 8 kV.     

2-D corona field computation in configurations with ionising and non-ionising electrodes

An efficient method is proposed for the computation of the electric field strength and of the space-charge density in configurations of at least three ionising and non-ionising electrodes. The physical model is derived under the assumptions commonly accepted for the study of corona fields. The mathematical model makes use of a conformal mapping that converts the actual boundary-free field zone into a rectangular domain with well-defined boundary conditions. The finite-difference method is then used for solving the differential equations that describe the ionic space-charge and electric field distribution. The computational procedure was employed for studying the simple case of the drift zone of the corona discharge generated between a so-called dual electrode and a grounded plate. The dual electrode consisted of an ionising wire (diameter 0.22 mm) located at 20 mm from a tubular metallic support (diameter 25 mm). The computed current–voltage characteristic and current density distribution at the surface of the collector plate were in good agreement with the experimental data obtained for this combined corona–electrostatics electrode arrangement.     

Electrostatic force acting on conductive ball between electrodes

To advance electrostatic applications such as novel printing technologies and solder ball control for LSI bumping, the electrostatic force acting on a conductive ball between two electrodes is calculated. The electrostatic force increases as the ratio of the ball diameter to the electrode separation increases. The electrostatic force is also calculated for the case when a charge pattern is formed on the insulating layer on the upper electrode. In this case, the electrostatic force initially varies as the square of the charge pattern area but eventually plateaus to a constant value as the area increases. Experiments investigating the force acting on the ball are performed. The force estimated from these experiments agrees with the value obtained by electric field analysis.     

Shrinking limits of silicon MOSFETs: numerical study of 10 nm scale devices

We have performed numerical modeling of dual-gate ballistic n-MOSFETs with channel length of the order of 10 nm, including the effects of quantum tunneling along the channel and through the gate oxide. Our analysis includes a self-consistent solution of the full (two-dimensional) electrostatic problem, with account of electric field penetration into the heavily doped electrodes. The results show that transistors with channel length as small as 8 nm can exhibit either a transconductance up to 4000 mS mm ^− 1or gate modulation of current by more than 8 orders of magnitude, depending on the gate oxide thickness. These characteristics make the devices satisfactory for logic and memory applications, respectively, although their gate threshold voltage is rather sensitive to nanometer-scale variations in the channel length.     

Formation of reactive species in gliding arc discharges with liquid water

The effects of gas composition on gliding arc (glidarc) electrical discharge reactors with pure water have been studied. The glidarc reactors utilized AC electrical discharges with two different electrode configurations. In one case a set of two stainless steel electrodes connected to a single power supply was placed in the gas phase over the liquid surface (power=250–300 W, maximum voltage=12 kV). The second experimental arrangement utilized a reactor with a set of three stainless steel electrodes supplied by two identical high-voltage transformers, where the electrodes were placed over the water surface or with the water sprayed directly in the plasma formed between the electrodes (power=500–600 W, maximum voltage=12 kV). The variation of pH and conductivity and the formation of hydrogen peroxide, ozone, nitrate, and hydrogen were measured. The effects of the type of gas, including pure oxygen, pure nitrogen, and dry air, were determined.     

Effective ultrasound electrochemical degradation of methylene blue wastewater using a nanocoated electrode

A novel sonoelectrochemical catalytic oxidation-driven process using a nanocoated electrode to treat methylene blue (MB) wastewater was developed. The nano-scale (nanocoated) electrode generated more hydroxyl radicals than non-nano-scale (non-nanocoated) electrodes did. However, hydroxyl radicals were easily adsorbed by the nanomaterial and thus were not able to enter the solution. Supersonic waves were found to enhance the mass-transfer effect on the nanocoated electrode surface, resulting in rapid diffusion of the generated hydroxyl radicals into the solution. In solution, the hydroxyl radicals then reacted with organic pollutants in the presence of ultrasonic waves. The effect of the nanocoated electrode on the MB wastewater treatment process was enhanced by ultrasound when compared to the non-nanocoated electrode used under the same conditions. The synergy of the nanocoated electrode and ultrasonic waves towards MB degradation was then studied. The optimum operating conditions resulted in a 92% removal efficiency for TOC and consisted of a current of 600 mA, an ultrasound frequency of 45 kHz, and a supersonic power of 250 W. The mechanism of ultrasound enhancement of the nanocoated electrode activity with respect to MB treatment is discussed. The reaction intermediates of the sonoelectrochemical catalytic oxidation process were monitored, and degradation pathways were proposed. The sonoelectrochemical catalytic oxidation-driven process using nanocoated electrodes was found to be a very efficient method for the treatment of non-biodegradable wastewater.     

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)₆³⁻) and hexacyanoferrate(II) (i.e., Fe(CN)₆⁴⁻) redox couple and 1 M Na₂SO₄ at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current–voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil<the Ir-coated titanium (Ti) mesh<the Pt-coated Ti plate<the graphite foil. Moreover, the Vulcan-coated graphite foil showed 5–10% higher power density than the metal mesh electrodes. From the polarization curve of the Vulcan-coated graphite foil electrode, it was found that total resistance decreased as thickness and geometric surface area of the electrode increased.     

Experimental observation of negative differential characteristic of corona discharge in ultraviolet spectrum

Corona discharge is a self-sustained discharge which appears at electrodes with a small radius curvature in gas insulation. An almost invisible glow occurs just above the inception voltage. Corona phenomenon is mainly used in electro-technological processes to obtain space charge for electrostatic precipitation, separation of different particles, electrostatic liquid or solid coating, neutralization of space charge, etc. All of these processes rely on a strong nonhomogeneous electric field generated by a point – plate electrode system. When the critical value of the applied voltage is reached, the ionization processes near the point electrode start and give rise to the current between two electrodes. If the pointed electrode is positive, it is possible to observe an anomaly of the current – voltage (I-U) characteristic for the point-plate space. It means that while the voltage is raising the current density decreases in a narrow voltage area (2–3 kV). The anomaly was technically named as negative differential conductivity (dI/dU < 0). Unstable current can have a negative influence on electro-technological processes. The anomaly was detected for different shapes and materials of the electrode as well as for various temperatures and distances between electrodes. An oxidation layer, which appears on the metal electrode, also influences the ionization processes near the pointed electrode and causes a decrease of a current. In this paper measuring of the discharge activity in a point – plate electrode system is presented. Ionization of gas atoms and molecules in a high electric field and the following recombination of electrons and positive ions in the corona region can give rise to high-energy photons which produce new electrons in the field of discharge. Corona discharges are detected by DayCor Corona camera which can register UV emission generated by corona in a day light. The experiment was conducted with various shapes of the pointed electrode and distances between the high voltage and the grounded electrode under applied direct voltage with positive and negative polarity.     

Über die Photoleitung von Anthrazen

The dependence of the photocurrent on voltage, light intensity and electrode separation and also the decay-time of the photocurrent is measured. All these measurements are largely influenced by the electrode material. The results obtained with Cu I- and Al-electrodes and also with insulating electrodes are given and the different behavior is discussed by means of a model. Hereby conclusions are made about the mean ranges and the mobility of the holes which are mainly responsible for the photocurrent.     

Corona discharge ion sources for fine particle charging

Charging of aerosol droplets and solid particles is applied in many industrial processes such as electrostatic painting, particle separation and electrostatic precipitation. In most of charging devices, electrical discharges are used as a source of ions, which are deposited onto the particles. In the present paper, the charging process by ionic current in alternating electric field was optimized experimentally. Alternating electric field charger was used as a charging device in these experiments. The current voltage characteristics of electrical discharge in this device, and the charge imparted to the particles were determined. The level of charge was measured at the outlet of the charger and was compared to the Pauthenier limit for different supply voltages, and frequencies. MgO powder was used as a source of particles in these experiments. It was noticed that higher supply voltage of the charger gives higher level of particle charge, but at the same time, the particle deposition on the charger elements was increased, decreasing the particle penetration. A compromise between these two tendencies is therefore necessary. As a result we have proposed a criterion maximizing the total charge born by the particles which is a product of relative particle charge and particle penetration.     

Sheet sticking caused by charge flow in a buried conducting layer

Electrostatic charge causes sheets to misfeed from the input stacks in inkjet and laser printers. Conductive layers within sheets that suppress discharges and reduce particulate contamination also aggravate sheet sticking. The surface potential of sheet media is a direct measure of the charge in the buried conducting layer. Our experiments find that the times characterizing the voltage transients range from 10 to 1000 s for conductive layers with sheet resistivities in the range from 10⁺⁹ to 10⁺¹¹ Ω/□. Our models predict that charge flowing in the conducting layer increases the electrostatic sticking force. Model predictions are in agreement with our experimental measurements.     

Organic dye removal from aqueous solution by pulsed discharge on the pinhole

Various active chemical species such as hydroxyl radicals, oxygen radical, hydrogen peroxide and ozone etc. can be produced by pulsed discharge. These active species can remove organic pollutants from the aqueous phase effectively. In present work pulsed discharge was formed on the pinhole of an insulating plate which was inserted between two plate electrodes. The characteristic of methyl orange decoloration by the discharge was investigated. The results of experimentation showed that peak voltage, pulsed frequency, initial solution conductivity and gas species impact the decoloration rate of the methyl orange (MO) significantly. The decoloration rate of MO solution is increased with increasing of the peak voltage, pulsed frequency, and decreasing initial solution conductivity. When the MO solution was treated with different gases bubbling, different decoloration rate was obtained and the order of decoloration rate is: oxygen > air > nitrogen.     

Non-adiabaticity in surface chemical reactions

Chemical reactions at surface may dissipate energy exciting electron-hole pairs in the metal substrate. Direct detection of the chemically induced hot charge carriers may be achieved by measuring the tunnel current in Ta–TaOx–Au tunnel junctions when the Au top electrode is exposed to an atomic hydrogen beam. A current of 1 nA cm^?2 was observed during a hydrogen exposure with a flux of 0.1 ML s^?1. The transient is related to the reaction kinetics and allows us to identify the elementary reaction steps causing the electronic excitations which are monitored by the observed current. Using Pt as top electrode material a markedly different transient is observed. Applying a bias voltage to the sensor allows spectroscopy of the electronic excitations. The experiments provide detailed insights into the non-adiabaticity of various reaction steps at a surface.     

Effect of gamma-ray irradiation on surface charge behavior of polybutylene naphthalate

Polymer insulating materials are widely used in radioactive environment. Surface charge accumulated on the material has been considered as an important factor for inducing discharge which may cause serious damage to electrical devices. Thus, from the safety point of view, it is necessary to investigate the charge behavior on polymer surface after the irradiation. In this paper, polybutylene naphthalate (PBN) was employed as test sample which was previously irradiated in air up to 100 kGy and then up to 1000 kGy with dosage rate of 10 kGy/h by using a ⁶⁰Co gamma-source. The experiment was carried out under a negative dc stress between two parallel electrodes. An electrostatic probe was designed to measure the charge density. Obtained results show that with the increase of the total dose of gamma-ray irradiation, the charge density and the storing capacity decrease. The charge accumulation depends upon the density of localized surface states, which is varied by the radiation induced cross-linking and degradation reactions of the molecule structure. The charge decay mainly relies on the recombination of surface charge with ions of opposite sign in surrounding air.     

平行板静电场法离子引出的对称收集

离子引出的研究在AVLIS工程中有重要的意义，离子引出量和引出时间直接关系到整个系统 的离子收集效率. 在静电场中，由于等离子体屏蔽效应的存在，等离子体电位要高于正、负 极板的电位，而且在靠近正、负极板的两侧均存在鞘层. 理论模拟表明在正极板一边也可以 引出离子. 选取铯（Cs）作为实验对象，研究静电场对Cs等离子体的离子引出，使用安装在 两个极板上的法拉第筒收集离子引出信号. 实验结果表明，正极板确实可以引出离子，随着 外加电压的升高，从正极板一边引出离子的比率降低. 关键词： AVLIS 离子引出 等离子体