Electrostatic atomization of conducting liquids using ACsuperimposed on DC fields

The objective of this study is to investigate the possibility of using electrostatic atomization to produce fine ceramic particles starting from highly conducting ceramic precursor solutions. The work was directed towards carrying out experimental investigation for the production of uniform droplets formed by the breakup of a permanent jet extending from the capillary nozzle. To control the atomization process an AC field (sine wave) was superimposed on a DC field. For given parameters of electrostatic field, capillary diameters, resistivity of liquids, and flowrate, the jet formation and breakup process was investigated. Several regimes were observed to be in synchronization with the applied potentials and frequencies. In these regimes uniform droplets were produced. Optical techniques were employed to study the breakup process     

Production of oil/water type uniformly sized droplets using aconvergent AC electric field

The authors proposed a new method to produce uniformly sized insulating liquid droplets (such as kerosene or plastic monomer) in immiscible liquid media (distilled water) by means of an applied convergent electric field generated using AC or pulsed voltage. The disintegration mechanism of the liquid column was observed precisely using video images and still photographs. Kerosene droplets with an essentially uniform diameter ranging from 100 to 250 μm were produced synchronously with the applied AC frequency using a nozzle diameter of 100 μm. When the flow rate of the co-flowing liquid surrounding the oil-phase liquid jet was increased, the synchronous frequency became higher and the size of the resulting droplets was decreased due to the elongation of the liquid jet. The disintegration mechanism is most likely the forced oscillation of the liquid jet stimulated by each cycle change of the applied voltage. The droplet size can be widely controlled by varying the AC frequency, nozzle diameter, liquid flow rate and velocity ratio between the oil-phase and co-flowing water     

Dielectric Liquid-in-Liquid Dispersion by Applying Pulsed Voltage

Liquid-in-liquid dispersion, such as organic liquid in water or water in organic liquid, has been performed using dc or ac voltage applied between nozzle and ground electrode. In the present study, pulsed high voltage was applied to produce droplets with controlled diameter in wide range. The high voltage pulse source was capacitor discharge type with 20 - 50 Hz and ranged from 0 to several kV. Water glass was atomized in alcohol solution into diameters ranging from several mum to sub-mm, depending on applied voltage. The atomized water glass droplets were solidified by removing water molecules from the water glass. Synchronized droplet formation with pulse frequency was possible by controlling pulse voltage, width and frequency, which produced uniform sized droplets successively. When the pulse voltage was raised, the droplet formation mode changed from the synchronized formation to dispersion mode through transient mode. In the dispersion mode, droplets of several mum diameter having high uniformity were produced. Utilization of high voltage and high-speed pulse to liquid-liquid dispersion could make it possible to atomize in a conductive liquid without electrolysis.     

Understanding discharges initiated by water droplet on epoxy nanocomposites under DC voltages adopting UHF technique

Corona inception voltage due to a water droplet on epoxy resin in an electrode gap is high under DC voltage compared to AC voltage. It is observed that, as the contact angle of the epoxy nanocomposite material becomes higher, the corona discharge inception voltage increases. The droplet movement is observed, using a high‐speed camera, on application of the voltage. It is seen that a droplet moves toward the ground electrode under an AC or a negative DC voltage, whereas it moves toward the high‐voltage electrode under a positive DC voltage. It is also observed that carbonization occurs near the ground electrode under AC and negative DC voltages, and near the high‐voltage electrode under a positive DC voltage. During the evaporation of the water droplet (during arcing) on the surface of the insulating material under AC and DC voltages, carbonization of material occurs and is high both in pure epoxy resin and in nanocomposites with 5 wt% epoxy clay. The magnitude of the arcing current is nearly the same irrespective of the percentage of clay in the epoxy nanocomposites. The magnitude of discharge current flow is high under negative DC voltage compared to positive DC/AC voltages. The rise time of injected current pulses, at the time of corona inception and during arcing, under AC/DC voltages, is a few nanoseconds. Ultrahigh‐frequency signals were emitted as a result of the corona discharge from the water droplet on epoxy nanocomposites and at the time of arcing between the droplets and the electrodes, both under AC and DC voltages, with its dominant frequency in the range 1–2 GHz. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

水煤浆雾滴群荷电特性的试验研究

利用针管–环状电极配置的微喷射流静电雾化系统对水煤浆雾滴群的荷电特性进行了试验研究,以雾滴群的荷质比作为衡量其荷电效果的指标,采用网状目标法获得了高压静电场强度、水煤浆电导率以及射流流量对水煤浆雾滴群荷电特性的影响规律。试验中发现充电电极在正向加压及逆向减压的情况下,水煤浆雾滴群表现出两种不同的荷电规律, 除起止电压之外,雾滴群在正向加压过程的荷质比均不同程度略小于同等条件下逆向减压过程的荷质比。研究还表明：环状充电电极加载25 kV以内的电压已经能使水煤浆射流在静电场以感应荷电方式有效充电,达到静电雾化的条件;相对高的感应场强、液体电导率以及较低的射流量能够使雾滴群获得较高的荷质比。     

Production of Nano-silica Particles in Liquid-liquid System by Pulsed Voltage Application

Electrostatic atomization in liquid-in-liquid media has been performed to produce fine droplets with narrow size distribution. The droplet diameter was controlled from mm to mum with applying dc voltage. When ac superimposed on dc voltage was applied, uniformly-sized droplets were produced. The high frequency pulsed voltage was effective to disperse liquid into nm-sized droplets. Water glass aqueous solution was dispersed in alcohol solution, and then they were solidified into solid particles by dehydration. The diameter of the dispersed particles was measured with a laser scattering particle analyzer. Particle diameter was depended on the applied pulse frequency and voltage, flow rate of the water glass, and water glass concentration. With increasing applied pulse frequency, the particle diameter and size distribution were decreased. Particles with 200 nm average diameter were produced at 1 kHz and 5.3 kV of applied pulse.     

Breakup of large water droplets by electric fields

The results are presented of an experimental study of the processes that lead to the breakup of a large water droplet doped with alcohol to approach the density of oil and immersed in an oil dielectric medium to which a strong electric field is applied. The study, which was carried out by means of photography, showed that the deformation of the droplets prior to breakup involves distinct characteristic stages of importance to the induction charging and to the ultimate charge separation phenomena. The experimental results show the conditions and the phenomena that lead to the breakup of an initially uncharged water droplet when subjected to an electric field that is not perfectly uniform and in a gravity field     

憎水性表面水珠的电场计算及放电研究

用ANSYS有限元分析软件对不均匀电场(针-板电极)中憎水性表面分离水珠的电场进行了计算,比较了无水珠、单个水珠以及多个水珠存在时憎水性表面沿面电场分布的变化情况,计算出水珠存在引起固、液、气三重介质连接点处的畸变,且水珠的存在对强场区电场的畸变作用更显著。同时在实验室中进行了模拟试验,用10000帧/s的高速数字摄影仪对整个放电过程进行了全程捕捉。结果表明,人工布液方式下憎水性表面分离水珠的放电是存在明显熄灭重燃现象并由两端向中间发展并沿水珠顶部贯通的细小电弧连接所致。     

Characterization of an electrodynamic balance for suspendingcharged droplets

The electrical characteristics of an electrodynamic balance used for suspending charged droplets were determined by constructing a computer model based on the charge simulation technique. This device is traditionally constructed with hyperbolically shaped endcaps and ring electrodes since an analytical solution exists for the electric field in this geometry. Using the charge simulation technique, other electrode shapes (some with observation portals) were evaluated for their effectiveness in suspending and stabilizing droplets. In this stability study, the motion of a droplet within the electrodynamic balance was evaluated using a numerical solution of the equations of motion for a droplet in the calculated electrodynamic force field. Four shape attributes were considered: electrode curvature; chamber size and geometry; and electrode extension. Three end cap curvatures were examined: flat, hyperbolic, and more steeply curved. Two principal findings are: (1) viewing ports should be embedded within an axially symmetric groove, in which case they do not affect the function of the balance; and (2) the voltage needed to balance a particle against gravity is a strong function of the chamber geometry     

Emulsification and Demulsification Processes in Liquid–Liquid System by Electrostatic Atomization Technique

A new electrical emulsification and demulsification apparatus using an electrostatic atomization technique was developed, and the investigation of both processes in a liquid–liquid system was conducted. First, fine water droplets were generated in silicone oil using a nozzle electrode with ac high voltage, and then, a stable water-in-oil (W/O) emulsion was produced without surfactants. The mode of electrostatic atomization and the trajectory of the fine droplets' flow were observed. The diameter of fine droplets and their distributions were measured as a function of the applied voltage and its frequency. Experiments indicated that electrohydrodynamic (EHD) induced liquid flow with water droplets played an important role in the formation of the emulsion. Next, the demulsification of W/O emulsion was carried out by two injections of oppositely charged water droplets, using the method of electrostatic atomization. The test liquid, which was prepared by the electrostatic atomization technique, was maintained in a state of emulsion for a longer time if no electric field was applied. When the positive- and negative-charged droplets were injected into the test liquid, the emulsion, with a dull color, gradually became transparent as time elapsed. The aggregated droplets fell down due to gravity and the EHD flow effect, resulting in the separation of water and oil. It was found that two injections of oppositely charged water droplets were effective for resolving the emulsion.      

高压脉冲负电晕荷电喷雾试验研究

为减少化学农药带来的污染,采用了荷电喷雾新技术。首先对负高压脉冲电晕荷电机理进行了理论分析,再用网状目标法通过调节电压、极距、电极直径、电极数目等参数进行电晕荷电试验,比较各因素对电晕放电伏-安特性影响及荷电后雾化效果;测量不同电压下雾滴的索太尔直径;并用高速摄影拍摄雾滴带电射流破碎时的状态,得到射流破碎时的雾滴形状。理论分析和试验结果表明,电压越高,雾滴谱较窄,雾滴粒径变细,均匀度越高;揭示了不同影响因素下的雾滴荷电特性,为负高压脉冲电晕荷电喷雾技术的应用和设计提供了理论基础和试验数据。     

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。     

Electric field and energy computation on wet insulating surfaces

The paper presents the results of electric field and energy computation on insulating surfaces covered by water in the form ranging from small discrete droplets to large wet patches. The goal of this study was to understand the differences in the flash-over performance of outdoor insulators, in particular nonceramic insulators, under contaminated conditions as a function of surface wettability. The computational algorithm is based on the charge simulation method. A decrease in the maximum electric field at the water droplet tip is obtained as the droplet size increases, however, the electrostatic potential energy increases with the size of the water droplet, which might increase the surface discharge intensity. The role of the coalescence of small water droplets into larger droplets and filaments on the electric field and energy has been investigated. The location of such larger water bodies with respect to the electrodes has been examined. These computations shed some light not only on the role of hydrophobic surfaces but also on the location of hydrophobic surfaces along the insulator on the flashover performance of outdoor insulators. It has been shown that these computations provide quantitative data that compliments information obtained from simpler techniques such as visual observation and surface resistance measurements, for the purpose of assessing the performance of insulators in service     

Electrostatic Generation of Fine Paint Droplets

Small vibrating capillaries have been used with good success to generate uniform liquid droplets as small as 20 ?m in diameter. However, this technique has not been successful for viscous highly pigmented fluids such as paints. Since paint tends to clog fine capillaries, the smallest droplet that can be reproducibly obtained with conventional methods is about 400 ?m. A method is described for electrostatically generating paint droplets down to 30 ?m. A 250 ?m diameter paint jet is vibrated by an electromechanical transducer at a frequency of 2200 Hz in the presence of an electric field. Fine ligaments are formed between the large drops. Under the action of the electric field the ligaments break up into small highly charged droplets which can be spatially segregated according to size. Calculations of droplet charge based on the equations of motion for the system indicate that the charge on the finer droplets approaches the Rayleigh limit.     

Electrostatic Droplet Growth in a Neutrally Buoyant Emulsion

Droplet growth is examined in a water-in-oil type emulsion where the droplets are subjected exclusively to viscous and dielectrophoretic forces. The latter are produced by the interaction of the droplets with an otherwise uniformly imposed electric field. Theoretical considerations are presented as a basis for understanding and interpreting the experiments. An emulsion consisting of deionized water droplets in a silicone oil of specific gravity I is subjected to a uniform 60 Hz, ac electrostatic field. Initially, the droplets are fairly monodisperse with mean diameters of approximately 25 , sm. The changes in droplet size distributions with time are examined with a laser diffraction system for water volume fractions ranging from 0.001 to 0.1 and applied fields ranging from 52 to 520 kVm-1. The average droplet size increases exponentially with time; we examine the exponent's dependence on average field strength and droplet volume fraction.     

Electrostatic actuation of liquid droplets for micro-reactorapplications

A device for the electrostatic transport and manipulation of liquid droplets on a solid surface is described. Arrays of microelectrodes are fabricated on a substrate, which is covered by a hydrophobic layer. Water droplets, typically a microliter in volume, take spherical shape on the surface and are caused to move by switching the voltage applied to the electrode array. The transport of droplets, deflection of a droplet in either of the bifurcating paths, and the mixing of two droplets by coalescence are experimentally demonstrated. The device can be used for microchemical reactors where transport, sorting and mixing of reagents constitute basic unit operation     

雨天交流输电线路电晕放电判据

电磁环境是制约特高压输电线路结构设计与导线选型的关键因素,通过高速摄像机和放电脉冲的同步观测,研究了水滴下落、附着和离开导线时的放电特征;利用有限元软件分析了水滴和导线之间的电场分布;基于有效电离积分分析了水滴位置、大小、导线电压对水滴滴落放电的影响,提出了水滴滴落放电的起始判据。研究发现,雨滴与导线之间的间隙放电产生的放电电流脉冲远高于雨滴附着在导线表面时产生的电晕放电,是造成雨天交流线路电磁环境问题的主要原因;伴随水滴的滴落过程,有效电离积分经历了一个先升高后降低的过程;有效电离积分的极值随电压的升高而显著上升,随水滴半径的增加而小幅增加。     

Formation of uniformly sized liquid droplets using spinning diskunder applied electrostatic field

A rotating multinozzle system that utilizes an applied AC potential combined with a DC bias to produce a large number of uniformly sized droplets synchronously with the applied AC frequency is proposed. A three-step experimental investigation is reported. The operational parameters were determined using a stationary single nozzle. Finally, using a rotating multinozzle system with 100 nozzles, a large number of uniform droplets was produced, and the uniformity was checked with a particle analyzer using the immersion sampling method. It was found that the synchronous region of the stationary single nozzle coincided with that of the rotating single nozzle (both nozzles had the same diameter and length). Therefore, one can predict the correct operational parameters for the rotating nozzle system from the results obtained in the stationary nozzle experiment (which are much easier to obtain). Uniformly sized droplets can be produced synchronously with an applied AC frequency using rotating nozzles. The operational parameters for the rotating single and multinozzles are almost the same     

Resonance phenomena of a single water droplet located on a hydrophobic sheet under AC electric field

Resonance vibration of a water droplet located on the surface of a hydrophobic sheet under an AC electric field was investigated experimentally. In order to confirm the effect of the surface property of hydrophobic materials on the resonance phenomena of a water droplet, three kinds of hydrophobic materials, silicone rubber (SR), polytetrafluoroethylene (PTFE), and polydimethylsiloxane-grafted fluoropolymer (PGF) sheet were used. A single water droplet with a volume ranging from 3 to 30 /spl mu/L was placed between parallel electrodes, where a tangential electric field was formed along the surface of the hydrophobic sheet. A water droplet under the AC field vibrates strongly only at a particular frequency range. The resonance frequency, when the water droplet vibrates, decreases with increasing the volume of the water droplet. The resonance frequency on the SR sheet is lower than that on the PTFE and the PGF sheet. The resonance frequency and the magnitude of the deformation of the water droplet depend on the surface properties of the hydrophobic material.     

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.