Harmonic spraying of conducting liquids employing AC-DC electricfields

This paper reports the results of the work carried out to investigate the breakup process of charged conducting liquid jet under the influence of an AC field superimposed onto a DC field. The main aim of this paper is to optimize the spraying parameters and to generate uniform droplets of highly conducting liquid in a controlled fashion by varying the strength and the frequency of the applied AC field. The electric field at the tip of a blunt needle facing a ground electrode was examined using a finite-element modeling technique. Three types of ground electrode configurations were investigated. A mathematical model for the electrostatic force on the leading edge of the droplet as a function of the liquid flowrate, the applied voltage, and distance between the capillary tip and the ground electrode has been developed. The breakup and droplet formation processes were investigated using a telemicroscopic lens and charge-coupled device (CCD) camera. The video data was processed using frame grabber software installed on a PC. The digital images were then analyzed utilizing image analysis software to give information on the breakup process and the size of droplets. A frequency range was identified where the formation of the droplets was synchronized with the applied AC field frequency. The effects of liquid flowrate on the synchronous bands were examined. The experimental results showed the dependency of the droplets size and the emission frequency on the applied AC frequency     

Formation of ceramic thin films using electrospray in cone-jet mode

An electrostatic atomization technique has been developed to generate ultrafine spray droplets of ZrO₂ and SiC ceramic suspensions in a range of a few micrometers with a narrow size distribution. The aim of this paper is to deposit uniform thin films (from a few micrometers to a few tens of micrometers) of these ceramic materials on alloy substrates. Compared to some other thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma spray (PS), etc., the thin-film deposition process using electrostatic atomization is not only cheap but also capable of depositing a very thin multilayer with abrupt interfaces. CVD and PVD are expensive techniques. They require either a high vacuum, even an ultrahigh vacuum environment or complex gas handling system. Their deposition rate is also low. PS is normally used to grow thermal barrier coatings which usually have a thickness of a few tens to a few hundreds micrometers. Its application is limited by the quality of the coatings (high porosity, coarse and nonuniform microstructure). Preliminary results in this work have shown that, for low through-put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution, which is crucial to produce uniform thin films. It was found that the size of ceramic particles in ZrO₂ and SiC thin films is less than 10 μm. Microstructures of these thin films show very homogenous morphologies. These results indicate that ceramic thin films with high homogeneity can be deposited using electrostatic atomization. It was also observed that the morphology of the underlayer has some influence on the morphology of the top layer     

高压静电液体雾化技术

高压静电雾化具有雾滴粒径细小、粒径尺度单一、空间弥散程度广等优点,广泛应用于农牧林业病虫害防治、工业喷涂、燃烧、脱硫除尘及材料薄膜制备等领域。为有效提高燃油燃烧效率、烟气脱硫效率及药剂灭菌效率等,从破碎动力学、不稳定理论及雾化模式等出发对高压静电雾化理论进行了详细的阐述,测试了平口雾化喷嘴在针-环状组合电极下的喷雾特性。获得了雾化角、射程、沉积量分布及雾滴荷质比、索太尔(SMD)平均直径和PIV雾化流场图象等信息,并进行了分析。实验结果表明:高压静电减小了液体的表面张力和粘滞阻力,使液体容易破碎成更为细小的液滴,使雾滴尺寸分布更均匀。雾滴荷电后,带电雾滴在高压静电场的作用下容易发生二次雾化,进一步减小雾滴粒径;同时带电雾滴在电荷之间斥力作用下,弥散程度加大,且能在目标物感应出与本身电荷极性相反的电荷,从而在极化力、引力等作用下更容易被目标物所捕获。     

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。     

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。     

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.      

阵列式多管集成静电雾化试验分析

为了减小甚至消除多管集成静电雾化（multiplexed electrostatic atomization,MES）中相邻毛细管荷电射流间电场的相互作用,探索和优化MES雾化特性,通过设计错位毛细管阵列来扩大喷雾源间距,并在静电场中加介质来减小射流排斥作用,改善了电场均匀性。对不同介质作用下MES的雾化特性进行了试验...     

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     

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。     

背负式静电喷雾器设计与试验

为改善传统背负式施药器械的喷雾效果,运用高压静电喷雾技术,设计了背负式静电喷雾器。该喷雾器由蓄电池、隔膜泵、高压静电发生器、喷枪、直射喷头和药箱组成,采用直接充电的方式对雾滴进行充电。为考察该喷雾器的性能,用网状目标法对荷质比进行了测量,用Oxford激光粒子图像分析测试系统测试了雾滴粒径及速度,最后用纸卡法测试了雾滴覆盖度。测试结果表明:荷质比随喷嘴压力的加大基本呈线性增长,因而在保证零部件及系统可靠的前提下,设计静电喷雾器时可适当增加喷嘴压力;静电促进雾滴吸附于作物表面、使雾滴粒径细小且分布均匀、改善了雾滴的速度分布均匀性,从而使雾滴能够均匀吸附于作物表面各部位,并显著提高了雾滴的覆盖度。     

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     

感应荷电过程中液滴雾化与荷电特性的相互影响

液滴的雾化与荷电特性直接关系到荷电液滴的工业应用效果。为研究感应荷电过程中两者的相互影响关系,在喷水质量流量不变的前提下,通过调节雾化压力改变液滴雾化特性,以网状目标法和粒子动态分析仪（PDA）作为测试方法和手段,系统地进行了液滴雾化与荷电特性相互影响的对比试验,并对荷电过程中的液滴回吸现象进行了研究。结果表明,在感应...     

水射流雾滴谱试验研究

利用LSA-III型激光粒度测试仪对水射流雾化的雾滴谱随速度和空间变化特性进行了试验研究,得到了雾滴谱液滴直径随速度增加而减小,随速度的增加变得更均匀的结果。雾滴谱的索特尔平均直径从轴心向两侧边缘变小,且上侧比下侧的更小,并随速度和离开喷嘴出口距离的增大,这种变化趋势在减弱。速度为27m/s和35.3m/s时射流雾化实际上处于风生破碎阶段,并由于二次雾化破碎,液滴直径沿轴向减小;速度为93.5m/s和121.6m/s时的射流二次雾化范围很短,并由于碰撞的原因,液滴直径沿轴向增大。     

Some Effects of Fluid Jet Dynamics on Ink Jet Printing

Synchronous ink jet printing systems use a small fluid ink stream, as produced by a pressurized ink through a small orifice, to produce ink images on a recording surface. The initial stream breaks up into a uniform sequence of similar droplets as a result of velocity variations injected by the orifice assembly. As the droplets form, individual droplets receive charges by induction. The charges imparted to droplets determine their flight path through an orthogonal deflection field to the recording surface or, alternatively, to an ink dump. The mechanism of drop formation, drop charging, drop deflection, and aerodynamic interactions between drops, and how these influence an ink jet printer's performance, are discussed. In addition, since the fluid dynamics limit the range of applications for ink jet printing, some limiting factors are described.     

双流体雾化荷电特性试验

为了有效改善石灰浆喷雾烟气脱硫中的浆液雾化,提高烟气脱硫效率,在引入双流体静电喷雾技术中,建立了环形电极的感应荷电的数学模型,计算了电极诱导的电位;采用目标网状法设计了雾滴荷质比Aq的测定装置,测量了不同浆液质量分数w(slurry)、气体流量Qg、液体流量Ql、荷电电压Uq下雾滴的Aq。结果表明,Aq随着Uq的增大而增加;在同一Uq下,Ql增大则Aq变小,Qg增加则Aq增大。随着w(slurry)的增大,Aq呈现下降趋势,在w(slurry)>1.0%时,Aq变化不明显。     

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.     

Formation of ceramic thin films using electrospray in cone-jet mode

The electrospray technique has been developed to generate fine droplets of SiC and ZrO₂ ceramic suspensions and to deposit these ceramic thin films and their bilayer on alloy substrates. SEM examinations of the microstructures of these thin films show that the films are very homogenous with a uniform particle size less than 10 μm. The deposition of a very thin bilayer with an abrupt interface indicates that the electrospray process can be well controlled. The theoretical prediction of droplet size and electric current is in good agreement with experimental results, indicating that fine suspension droplets can be generated in the cone-jet mode. Therefore it can be concluded that electrospray is a promising technique for the preparation and controllable distribution of uniform ceramic thin films and coatings with the added advantage of low cost. It could find a wide range of industrial applications in the future     

Experimental investigation of droplet formation mechanisms byelectrostatic dispersion in a liquid-liquid system

Droplets having high uniformity and a widely controllable size range (from millimeters to micrometers) were obtained by means of electrostatic dispersion in an oil-in-water system, as reported previously by the authors. In liquid in-gas systems, many studies reported that the electrostatic force acting on the liquid due to the surface charge seemed to be the main factor affecting the atomization. However, using distilled water as a continuous-phase liquid causes the theoretical analysis to be very difficult, because distilled water has high conductivity and permittivity. Therefore, in the present study, experimental work is carried out on dispersion mechanisms in an oil-in-water system. The main factor affecting the atomization is considered to be electrohydrodynamic flow of continuous-phase liquid (distilled water) around the capillary nozzle tip. The amount of electric charge on the dispersed-phase liquid (kerosene) is considered to be negligible because of the very short relaxation time of the surrounding continuous-phase liquid. It is suggested that the droplet size and frequency distribution can be controlled by adjusting the operating conditions (applied voltage) and design parameters (nozzle shape)     

活化器中钙基吸着剂的增湿活化过程模拟

建立了一维活化器中吸着剂颗粒的活化效率预测模型。模型全面考察了水雾蒸发、减速、粒径分布以及液－液凝并等的影响。计算结果表明,液滴初始直径和初速度对颗粒活化效率有最大的影响,使用大粒径、窄分布和高初速度的雾化方式可强化增湿活化效果。通过对颗粒活化效率与实测脱硫效率的相关性分析,证实了活化颗粒的溶液反应是脱硫过程的主要机理     

静电喷涂中油液的电晕荷电及雾化试验研究

为了研究静电喷涂过程中油液的电晕荷电特性和雾化现象,利用静电涂油机为试验平台,分析了静电涂油机中梁板电极的电晕放电过程,得到了静电涂油机电晕放电的起晕电压;同时依据静电学原理,给出了液滴在高压静电场中的电晕荷电量和液滴破碎的理论临界场强;结合静电涂油机喷涂试验,从宏观和微观的角度分析了油液的雾化过程。研究表明,随着电压的增大,射流长度总的趋势是减小的,但在不同区域,电压对射流长度的作用不同;雾化角随电压增加而先增大到一定程度后开始减小,最后逐渐趋于稳定;电晕荷电电流随电压的增大而变大;雾滴粒径随电压的增加而减小,当电压在65kV左右时,粒径较小且分布最为均匀,此时油液达到较好的雾化效果。