感应荷电喷雾静电场与荷电特性分析

感应荷电喷雾静电场的特性是感应荷电喷雾流场与静电场耦合计算的基础,也是荷电喷雾技术基础理论研究的关键之一。为了了解喷雾静电场中环状电极的感应静电场分布特性,在感应荷电机理分析和静电场物理模型建立的基础上,通过将商用FLUENT计算功能的扩展,对感应荷电喷雾中喷嘴与环状电极静电场进行数值模拟,并对静电场分布特性进行分析,结合感应荷电机理,明确感应静电场分布对喷雾液滴荷电效果的影响,从而可以通过改变静电场的分布特性改善液滴荷电质量。计算结果表明:随着充电电压的增加或电极间距的减小,电极处电场强度增强,尤其是喷嘴电极处增幅明显;电场强度沿轴向衰减迅速,故拥有高场强的电极及其附近区域是液滴感应荷电的关键,研究结论与有关试验结果相符合。因此,较高充电电压或较小电极间距(10mm以下)情况下的喷嘴与环形电极的静电场分布有利于获得较好的荷电效果和喷雾质量。     

高压静电聚结破乳技术

为提高原油的电脱水效率,控制乳状液破乳程度,根据电破乳机理推导出液滴在交流电场中碰撞聚结及变形破裂的规律并分析了影响液滴运动特性的因素。研究中用设计的紧凑型静电聚结管道,对油包水乳化物施加50 Hz高压交流电,通过调节聚结管道电极板间所加电压及极板间乳化物流量qV观察液滴大小的变化规律,并计算乳化物通过聚结器前后的时间对液滴颗粒粒径的影响。结果表明,场强升高可增大液滴直径提高液滴聚结效果;但增大到一定程度时会发生电分散影响脱水效果,故应控制场强在一定范围内使得液滴聚结以提高脱水效率;同时液滴在电场中的停留时间也对聚结效果有明显的影响。     

基于圆锥管状电极的高压静电场对雾滴荷电的影响

静电喷头电极产生的高压静电场对雾滴荷电及沉积效果有重要影响,为此,根据航空静电喷雾的特点改进原有圆柱管状电极型式为圆锥管状电极。借助Ansoft Maxwell软件和试验测试方法对锥形管状电极的空间电场强度进行分析。建立了基于圆锥管状电极静电喷头的雾滴荷电效果测试系统,开展了模拟飞行条件下的充电电压对雾滴荷质比及沉积分布的影响效果试验研究。结果显示:电极空间电场模拟结果与测试计算结果基本符合,确定靠近锥形电极20~70 mm范围为最佳荷电区域。雾滴荷质比随着充电电压的增加有增加的趋势,与距离喷头的轴向位置关系不大,当电压达到10 kV时雾滴荷电饱和,并获得了最大荷质比2.13 mC/kg。相比0 kV条件,10 kV电压条件下的雾滴在中性靶标侧面、下面和背面的沉积量有明显提高,分别平均提高了18、19、18 cm-2;雾滴在正极靶标的沉积量明显多于负极和中性靶标,在正极靶标背面上的平均沉积量相比其正面和侧面增加的更多,达到86%。     

高压静电雾化雾滴粒径双峰分布概率密度模型

为预测毛细管—环电极配置的高压静电雾化系统下水静电雾化雾滴粒径的分布规律,采用颗粒动态分析仪测试了该系统的雾化雾滴粒径。当环电极电压在15~25 kV之间时,静电雾化模式为泰勒锥射流模式,雾滴粒径呈显著双峰分布规律,对此利用一种可双峰分布的概率密度函数建立了预测该模式下粒径分布规律的统计学模型,并与试验数据对比进行了误差分析,讨论了误差原因。结果表明:随着电压的增加,电场力耦合因素的影响将导致误差增大;在每个电压工况下最大误差均出现在双峰之间的谷值附近,但均<15%,总体上该模型能较好地与试验数据相符。     

农用高压荷电雾滴形态特征与沉降运动分析

针对农用高压静电喷雾器械在雾化性能检测方面存在的不足,基于药液雾化场的实验数据,提出了利用激光粒子图像技术获取雾滴特征参数,再结合数字图像处理技术对雾滴运动情况进行分析的检测统计方法.以EES温室高压静电喷雾场中雾滴沉降区的雾滴形态特征及其运动为研究对象.运用Oxford激光粒子图像分析测试系统(PDIA)对图像中的雾滴直径、周长、形心位置、圆形度等特征参数进行计算与统计.同时,利用标记点跟踪和雾滴邻域匹配慨率方法对雾滴的运动轨迹进行拟合与分析.实验结果表明,该方法实现了对静电喷雾场中雾滴形态特征的快速准确检测,为进一步分析荷电雾滴的沉降及漂移运动提供了有效方法.     

Electrostatic Beneficiation of Coal Using a Cyclone-Tribocharger

A preliminary study is presented on a new method of separation of mineral inclusion from coal. The separation process involves triboelectrical charging of pulverized coal by a cyclone-tribocharger and electrostatic differential deflection of the coal. The separation tests for a pulverized Australian coal with 18.5 percent ash content using this separator yielded the following results: a cyclone with a copper wall gives the best separation performance; the percentage ash contents of particles collected on the anode and cathode of the separator are 26 percent and 11 percent, respectively; a coarse pulverized coal with 74-150 pm diameters showed a beneficiation rate better than that for a fine pulverized coal with diameters below 44 pim. In order to understand these results, the authors experimentally examined charging behavior of pure mineral particles fed to the cyclone-tribocharger with either copper or teflon walls and to a fluidization-charger. Avoidance of particle-to- particle collision and choice of cyclone wall material are important in raising the separation performance. On the basis of microscopic observation, the authors confirmed liberation of most mineral inclusion from coal crashed to particles of less than 70-?m diameters.     

Bipolar Structure of a Back-Discharge Field in an Electrostatic Precipitator

The current densities of positive and negative ions i+ and i- in the back-discharge field of an electrostatic precipitator (ESP) are measured with a bipolar current probe. The ratio i+/i- rises with increasing total current density i (= i+ + i-) in the streamer-mode back discharge, but it remains almost constant (10-20 percent) in the glow-mode back discharge. The probe-measured values of the back-discharge-starting current density are slightly higher in pulse charging than in dc charging. In addition, the pulse charging does not cause back discharge at a resistivity below 1013 ?cm. However, beyond 1014 ?cm the back discharge can hardly be avoided, even by pulse charging. The probe diagnosis of i+/i- in an ESP enables an approximate estimation of the charge-to-mass ratio of dust and the collection performance when i+/i-, averaged in space, is used.     

High-Voltage Monitoring in Electrostatic Separators

High voltage is known to be one of the main control variables in any electrostatic-separation process. From this perspective, the aim of this paper is twofold: to develop an effective high-voltage monitoring system and to demonstrate that it can be a useful tool for controlling the overall operating conditions of an electrostatic-separator system. A custom-designed virtual instrument was employed for processing the experimental data provided by a high-voltage probe, the output of which was connected to an electrometer. In several experiments, the output of the high-voltage probe was also connected to a digital oscilloscope, in order to obtain a better understanding of the variation of the electrode potential after a spark discharge. The laps of time without corona discharge and/or with low electric field intensities could thus be accurately determined, and the impact of the spark discharges on the outcome of the separation process evaluated. The dispersion of high-voltage measured values was found to increase in the presence of the material. The statistical analysis of the data revealed a significant correlation between the standard deviation of the high-voltage and the concentration of metal in the processed material. The results of this paper could be helpful for those seeking the optimization of the operating conditions for the electrostatic separation applications, in which the metal content in the feed materials exhibits substantial fluctuation with time     

Conducting Spheres in Electrostatic Fields

The problem of finding the resulting electrostatic potential outside a conducting sphere when the sphere is introduced into a known field is usually attacked by placing suitable image charges and dipoles at specially chosen points within the sphere. Thus, for example, to determine the field due to a point charge e outside an earthed conducting sphere, the standard procedure is to place a point charge é at the corresponding inverse point and to determine é by making the surface potential of the sphere zero. To the student, this method seems very indirect and not very obvious, and it has the additional disadvantage of depending on special geometrical properties of inverse points in a sphere.     

固定间隙的空气式静电放电

为更好地研究空气式静电放电,利用新型ESD模拟测试系统研究了固定间隙的空气式静电放电特性。在较宽范围的电压电平下,用数字存储示波器测量放电电流的上升时间、峰值、自制金属半圆环上的耦合电压峰-峰值,并记录了放电电流和耦合电压的波形。分析测量结果及其与放电电压和放电间隙之间的变化关系,可知在一定的间隙间距上,放电电流随着放电电压的增大而增大,高压放电也能产生上升沿比较陡的电流脉冲;在一定的放电电压下,存在着一个放电间隙间距使得放电电流峰值最大或耦合电压最大;不同电压下的频谱分布和能量分布不一样。     

化工生产中的防静电接地

化工生产的特点是在生产过程中经常接触酸、碱、有毒有害、易燃易爆的危险品。在生产过程中由于工艺、装置、人员的因素会产生静电。有时由于静电得不到有效的控制就有可能酿成重大事故。因此,在化工生产中要充分重视静电的危害性,制定出切实可行的消除措施。防止静电的措施(1)     

The Effect of Back Corona in a Laboratory Scale Electrostatic Precipitator

The results are presented of a study on the influence of back corona on the performance of a laboratory scale wire-plate precipitator, with the plate to plate spacing as a parameter. Back corona is introduced into the precipitator by increasing the ash resistivity, attained by increasing the ash-laden gas temperature from 21 ° C (a no back discharge condition) to 104 ° C. Performance is evaluated in terms of the Deutsch migration velocity and using the particle concentration measurements made at the inlet and outlet of the precipitator with an optical counter. Results for the four different plate spacings with no back discharge show a time-independent migration velocity and current density, with higher migration velocities for the wider plate spacings. Results with back discharge show an initially rapid decrease in migration velocity with time, accompanied by a rapid increase in the current density, with greater decreases for the wider plate spacings. The behavior of the precipitator with and without back discharge is consistent with the space charge model interpretation of the wide-plate spacing precipitator.     

Increasing Pile Density in Electrostatic Flocking by Introducing a Guiding Electrode

The physical performance of flocked fabrics increases greatly as the number of fibers flocked per unit area increases. With current electrostatic flocking techniques, the greatest pile density that has been achieved contains only about 23 percent of the maximum theoretically possible in a random impingement process. By inserting a third electrode, the strength of the electric field in the lower part of the flocking zone can be increased without causing a corona discharge. As a result the added electrode directs the fibers more effectively onto the substrate so as to increase the flocking density. In the experiments reported here, the flock density was increased by an average of 18.6 percent, ranging from 7.1 percent to 38 percent.     

Droplet charge-to-mass ratio measurement in an EHD liquid-liquidextraction system

The application of a high voltage electric field to enhance the rate of mass transfer in liquid-liquid extraction has been an active subject of investigation in recent years. The electrohydrodynamic (EHD) forces generated by electric fields at a liquid-liquid interface have a potential application in chemical processing industry solvent extraction processes. In this work, the charge-to-mass ratio of droplets formed in an EHD liquid-liquid extraction system has been investigated experimentally and theoretically. The results reported from the present investigation, extending from the single discrete droplet regime (at low applied voltages) to the dispersed multi-droplet regime (at high applied voltages), indicate that the modified Rayleigh instability model and Vonnegut and Neubauer model can explain maximum droplet charge acquired in liquid-liquid systems, especially the modified Vonnegut and Neubauer model which can predict most of the experimental results when the applied electric field is high enough and EHD forces become dominant     

Harmonic Effects in Electrostatic Induction Motors

Abstract

Electrostatic Induction motors are closely connected in theory to the familiar Tesla induction machine. In practice, designs are constrained by dielectric breakdown. Stator and rotor electrodes must be positioned to avoid breakdown rather than to provide sinusoidal distributions. The result is that Space and time harmonics are important in electrostatic machines. A cylindrical and in experimental electrostatic Induction motor is described. The electric field the air gap is used to compute theoretical torque, which is less than 4 mN · m under most conditions. Experimental operation with balanced three-phase excitation and bearing friction as the only load agrees with the theory more closely than in previous work.     

Numerical Simulation of the Electrohydrodynamic Flow in a Single Wire-Plate Electrostatic Precipitator

In this paper, the electrohydrodynamic (EHD) flow in a single wire-plate electrostatic precipitator has been analyzed numerically by employing a hybrid Finite-Element Method-Method of Characteristics numerical algorithm and the commercial computational fluid dynamic software FLUENT6.2. Parameters defining both the electric and the flow fields were predicted. The interaction between the electric and the flow fields has been discussed by adopting the proposed two-way coupling algorithm. With the help of the dimensionless analysis, an entire flow regime map has been developed for different Reynolds (Re) and EHD numbers. It was found that, at very low Re (15) and high EHD (2000) (based on the corona wire) numbers, the EHD flow dominates in the channel; as Re increases, the significance of the EHD wakes gradually decreases; at a higher Re (50) or a lower EHD (500) numbers, the EHD flow becomes the near-corona-wire phenomena, and the main flow dominates the channel. The possible influence of the EHD flow on the particle-collection efficiency was also discussed.     

Electrostatic discharge issues in electric vehicles

Electrostatic discharge (ESD) is an important issue in any motor vehicle. Anecdotal reports abound of cars with spark ignition hazards because of fuel tank designs, and even toll collectors reluctant to collect money by hand from certain late model cars. As electric vehicles move from the laboratory and test track to the production floor and showroom, ESD concerns take on a new context and become more critical. In this paper, the attributes of electric vehicles that give rise to concerns about ESD are introduced. When the concerns are taken into account, certain basic design constraints become evident. A candidate design is analyzed for its ESD properties. Some common design practices, especially the practice of isolating the battery bus, can create reliability problems because of ESD     

Electrostatic properties of ultra-thin polyimide Langmuir-Blodgettfilms biased in a needle-plane electrode system

Surface potentials of polyimide (PI) Langmuir-Blodgett (LB) films on metal (Al, Ag and Au) electrodes, charged at various voltages, were examined under a needle-plane electrode system. It was found that PI LB films were negatively charged when the biasing voltage applied to the needle-electrode increased. The surface potentials saturated when the number of deposited layers was 20 to 30, and they were dependent on the nature of the metal electrodes. The temperature dependence of the surface potential also was examined, and it was concluded that the tendency to accept electrons increases as the temperature increases. These results suggest that the presence of interfacial electrostatic space charges in as-deposited PI LB films at the metal/film interface made a significant contribution to the creation of the additional electrostatic potential when the films were biased under a needle-plane electrode system     

燃气轮机进气静电除尘系统

多年来燃气轮机进气清洁研究一直未取得重大进展。通常，燃气轮机是采用纤维过滤器滤除空气中的杂质，但这种方式存在许多不足。目前，有一种基于静电除尘技术的新方法，它与传统的纤维过滤器相比具有结渣少、空气预热量需求小、压降小及无需更换过滤器等许多重要的优点。     

Numerical and Experimental Study of a Continuous Electrostatic Smoking Process

The smoking process is a batch one with long duration processing (some hours). Deposition of smoke particles can be enhanced by electrostatic precipitation. However, a better knowledge of the fundamental physics is needed to optimize the process. We carried out experimental and numerical studies to obtain essential information on the smoke flow. First, experiments physically characterized the wood smoke. These measures lead us to study the turbulent two-phase flow using an algebraic slip model. The main coupling with electrical forces is taken into account through the slip velocity. Various assumptions were tested concerning the coupled phenomena in order to build an algorithm that is able to simulate these phenomena. Numerical resolutions are compared with data from the literature on a simple electrostatic precipitator (three wires between two plates). Simultaneously, experiments were performed on a simplified scaled-down model of the smoking process (wires and one plate). The results of particle image velocimetry show clearly that the electrostatic precipitation phenomenon is effective above a threshold voltage and is significantly influenced by geometry of electrodes. Experiments and numerical resolutions underwent a validation phase. A small-size industrial demonstrator, of which the promising results will not be discussed in this paper, was conceived by exploiting the presented works.