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。     

Drop-charge correlations for polydisperse electrostatically atomized liquid sprays

In many applications liquid sprays are atomized using electrostatic methods, and typically these spray plumes containing drops that have a range of diameters. To understand and predict the dynamics of polydisperse electrically charged spray plumes, knowledge of how the electrical charge is distributed amongst the drops is required. This has been achieved by post-processing phase Doppler anemometry data for two electrostatically atomized liquid sprays and fitting the drop diameter-charge correlation to an assumed relationship of form q=AD/sup n/, Here q and D are drop charge and diameter and n and A are empirical constants that describe the correlation. Values of n and A were calculated to be 2.1 to 2.9 and 5.8 /spl times/10/sup -5/ for a spray of specific charge 1.8 C/m/sup 3/ and 2.1 to 3.2 and its value of A is 2.5/spl times/10/sup -4/for a spray of specific charge 1.2 C/m/sup 6/. It was found that the mean drop charge, for all drop diameters, for both data-sets, was almost always less than the drop Rayleigh limit. This latter fact gives confidence in the procedure used since no restriction was placed on this parameter during the processing. We also estimate the distribution of drop charge about the mean value and as a function of diameter and suggest that small drops possess higher rms charge levels.     

Reducing Water-borne Paint Contamination in Electrostatic Rotary Atomizers

The electrostatic rotary atomizer has the highest paint efficiency in all kind of atomizers. The usage of an electrostatic rotary atomizer, therefore, has contributed to reduce the waste of paint and volatile organic compounds (VOCs). Concurrently, water-borne painting processes which use water-soluble paint have been introduced to reduce the amount of VOCs emissions. With the water-borne painting, the atomizer body is easily contaminated by the paint mists. The contamination has been an important problem to be solved in factories. In this report, the causes of water-borne paint contamination was considered and the experimental results of the contamination proof system were presented. The atomizer is surrounded by the repelling film that is charged and repels the incoming paint droplets which otherwise contaminate the atomizer. From the experimental results, following electrical properties are found to be important for the repelling film such as low capacitance and high insulation property to keep high surface potential. These features were also checked by the space charge measurements inside the repelling film. In addition, safety against incendiary sparking was investigated. The ground electrode of sphere, needle or blush-shape was approached to contact to the charged film. Energy of the discharge was calculated from the measured discharge current and the surface potential of the film. The discharge energy of all measured electrodes was below the minimum ignition energy of 0.24 mJ used in the painting industries. At the meantime, the results indicate that shape of the electrode is an important parameter to affect the discharge energy.     

用电子束辐照注入电荷包研究低密度聚乙烯中的电荷迁移率

通过研究外加电场强度50k V/mm以下低密度聚乙烯中的空间电荷包行为,使用一种多层结构的受辐照的双面粘贴聚氟乙烯薄膜低密度聚乙烯样品,通过电子束辐照在样品内部形成"波包"分布,在外加电场强度较低时形成电荷包,使用激光压力波法监测电荷包迁移。结果表明,以电荷包峰值位置为参考点,在样品内实际电场下电荷包平均迁移率分布范围为(0.17~3.01)×10?15m2/(V·s)。通过对不同外加电场强度下的空间电荷包行为的研究得到,电荷包迁移速率与电场强度关系符合负微分迁移率假设模型,从而证明了在较低的电场强度下负微分迁移率模型的正确性。     

Measurement of particle size and electrostatic charge distributionson toners using E-SPART analyzer

Performance characteristics of a laser-based instrument called the electrical-single particle aerodynamic relaxation time (E-SPART) analyzer for measuring aerodynamic size and electrostatic charge distribution of particles in real time and on a single-particle basis are described. Applications of this analyzer along with experimental data of the characterization of different toners for their size and charge distributions are presented, including operational principles and methods of data acquisition. Size distribution ranged from 2.0 to 20.0 μm in aerodynamic diameter, and the charge-to-mass distribution ranged from 0 to ±20 μC/g. The method is noncontact and provides both magnitude and polarity of electrostatic charge on an individual particle basis. The aerodynamic diameter and charge are measured simultaneously at an average count rate of approximately 100 particles/s     

Temperature effect on space charge dynamics in XLPE insulation

This paper reports on space charge evolution in crosslinked polyethylene (XLPE) planar samples approximately 1.20 mm thick subjected to electric stress level of 30 kV_dc/mm at four temperatures 25, 50, 70 and 90 degC for 24 h. Space charge profiles in both as-received and degassed samples were measured using the laser induced pressure pulse (LIPP) technique. The DC threshold stresses at which space charge initiates are greatly affected by testing temperatures. The results suggest that testing temperature has numerous effects on space charge dynamics such as enhancement of ionic dissociation of polar crosslinked by-products, charge injection, charge mobility and electrical conductivity. Space charge distributions of very different nature were seen at lower temperatures when comparing the results of as-received samples with degassed samples. However at higher temperature, the space charge distribution took the same form, although of lower concentration in degassed samples. Space charge distributions are dominated by positive charge when tested at high temperatures regardless of sample treatment and positive charge propagation enhances as testing temperature increases. This can be a major cause of concern as positive charge propagation has been reported to be related to insulation breakdown     

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。     

Charging and discharging of insulating particles on the surface of a grounded electrode

The aim of the present paper is to analyze the corona charging of millimeter-size insulating disks, as well as their discharging when they are no longer exposed to the action of an external electric field. The experiments were carried out on a roll-type electrostatic laboratory separator, equipped with a wire-type corona electrode, simulating the actual charging/discharging conditions in an industrial unit. Disks of various sizes were charged on the surface of the roll electrode, then the high voltage supplied to the corona electrode was turned off and the particles were collected in a Faraday pail, connected to an electrometer. The charge measurements were performed at various time intervals from high-voltage turn-off. In this way, the charge decay could be recorded and the discharge process fully characterized. The measured data show that the discharge process depends on the nature, size, and shape of the particles, as well as on the contact conditions between the particles and the grounded roll electrode. These data could guide the design of the electrostatic separation experiments that precede any new industrial application of this technology.     

Space charge behavior in low-density polyethylene

The space charge distribution in low-density polyethylene (LDPE) was measured with the pulsed electroacoustic (PEA) method. We used three types of LDPE: LDPE-L and LDPE-H were prepared by the high pressure process, and m-LDPE was polymerized with a metallocene catalyst. Space charge in LDPE strongly depended upon the electrode material. Semiconductive electrodes enhanced carrier injection into LDPE and, as a result, space charge. The density, polymerization process, applied field, temperature and so on also affected the space charge behavior. This space charge behavior was compared with the results of dc current measurements     

Effect of Charge Injection Due to ESD on the Operation of MEMS

The relative effect of charge injection due to human-body model electrostatic discharge (ESD) on the operation of capacitive microelectromechanical systems (MEMS) structures is studied. The influence on the operating characteristics as a function of feature size is analyzed; for small gaps (< 5 mum), the modified Paschen's law applies. A force factor is introduced to compare forces due to the control voltage and trapped charge due to ESD or triboelectrification and assess possible failure due to stiction. The results show that the relative effect of injected charge due to ESD increases inversely as the square of the gap separation for floating targets and inversely as the square of the plate area for grounded targets. For comparison purposes, the relative effect of charge injection due to triboelectrification is shown to be independent of device scaling. An electric-field model for the air gap and dielectric layer is introduced to assess the reliability of MEMS due to trapped charge in the dielectric.     

Laser tissue welding: laser spot size and beam profile studies

Evaluates the effect of laser spot diameter and beam profile on the shape of the thermal denaturation zone produced during laser tissue welding, 2-cm-long full thickness incisions were made on the epilated backs of guinea pigs in vivo. India ink was used as an absorber and clamps were used to appose the incision edges. Welding was performed using continuous-wave 1.06-μm, Nd:YAG laser radiation scanned over the incisions to produce ~100-ms pulses. Laser spot diameters of 1, 2, 4, and 6 mm were studied, with powers of 1, 4, 16, and 36 W, respectively. The irradiance remained constant at 127 W/cm². Monte Carlo simulations were also conducted to examine the effect of laser spot size and beam profile on the distribution of photons absorbed in the tissue. The laser spot diameter was varied from 1 to 6 mm, Gaussian, flat-top, dual Gaussian, and dual flat-top beam profiles were studied. The experimental results showed that 1-, 2-, 4-, and 6 mm-diameter spots produced thermal denaturation to an average depth of 570, 970, 1470, and 1900 μm, respectively. Monte Carlo simulations demonstrated that the most uniform distribution of photon absorption is achieved using large diameter dual flat-top beams     

Electrostatic deposition of CVD particles for fabrication ofultrafine ceramic filter

A novel method for forming a ceramic membrane was devised. Ultrafine particles of silicon nitride synthesized by thermally activated chemical vapor deposition (CVD) were deposited on an outer wall surface of a porous ceramic tube (substrate) by electrostatic force and sintered in an inert gas atmosphere. The ceramic-made electrode assembly using surface discharge was used for charging ultrafine particles at an elevated temperature. Special ceramic membranes with a three-dimensional network for use as a fiber filter were obtained by this method. The effective pore size was around 0.2-1.0 μm in diameter, and its porosity was extremely large. This structure has the advantage of allowing microfiltration with a very low pressure drop     

Direct observation of time-dependent space charge profiles in XLPEcable under high electric fields

Space charge distribution was measured, applying an electric field of >1 MV/cm to 3 mm thick XLPE cable insulation. Improving the conventional pulse electro-acoustic method, a new method was developed to measure space charge when applying HV to cables. Under high field, hetero charges were formed soon after voltage application, followed by an injection from the cathode. Then intermittent injections of charge packets from the anode took place. The space charge distribution kept changing without becoming stabilized. A simulation was done assuming hysteresis of the injection characteristics. The observed intermittent injection near the anode was qualitatively reproduced using computer simulation     

Characterization of tribocharging properties of powder paint

The charge-to-mass ratio (q/m) of individual particles plays a vital role in the powder coating process. Simultaneous measurements of particle size and electrostatic charge were performed on triboelectrically charged powder paint and other powders in the particle size range 1.0 to 65.0 μm in diameter. An electrical single particle aerodynamic relaxation time (ESPART) analyzer was used to measure electrostatic charge (q) and aerodynamic size (d_a) distributions on a single particle basis and in a noninvasive manner. The powders were triboelectrically charged against nonconducting surfaces. Experimental data show that (1) the magnitude of the charge increases linearly with the surface area of the particle and consequently, the charge-to-mass ratio of the particles decreases inversely with respect to d_a in the entire size range, and (2) twenty to sixty percent of the particles were charged with opposite polarity. The average charge attained by particles larger than 4.0 μm in diameter was less than the Gaussian limit of saturation charge. The charge-to-mass ratio of the bulk powder sample depends upon the range of particle size in the sample. The mass median aerodynamic diameter of the sample studied was 30.0 μm with the geometric standard deviation of 2.0     

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)     

Adhesion of charged powders to a metal surface in the powdercoating process

Substrate-particle adhesion of electrostatically charged, nonconducting particles deposited on electrically grounded substrates is discussed. Glass microspheres of diameters ranging from 25.5-74.1 μm, charged by corona and tribe-charging, were deposited in a monolayer on conducting stannic-oxide coated surfaces of glass plates (NESA). The total force of adhesion due to electrostatic, van der Waals, and gravitational forces was measured by observing the removal of particles by applying a known electric field between the particle coated surface and a clean surface of a second NESA glass, placed parallel to it at a distance of 0.013 m. The adhesive force was measured as a function of particle size and charge. The net average charge on the particles was measured using a Faraday cup. The experimental values agree well with the calculated force of adhesion for a single layer deposition. The charge decay of the particles was studied using a noncontact electrostatic voltmeter. The charge relaxation time of the deposited powder was found to increase with time. A physical model of the adhesion of charged powder paints deposited on a grounded metal substrate is presented. The role of the forces acting on a spherical polymer particle deposited on the surface of a uniform coating of powder paint is investigated as a function of particle diameter and charge. The particles are assumed to be unipolarly charged and deposited uniformly on the substrate. The relative magnitudes of the electrostatic attractive and repulsive forces are analyzed as functions of powder film thickness and particle size     

固定翼飞机静电分布及着陆泄放研究

为了研究固定翼飞机静电分布特性及着陆时静电泄放,在论述了固定翼飞机空中飞行时的静电产生机理、飞机静电的消散形式后用矩量法分别求取了飞机空中飞行、停靠地面时的电荷分布;获得了飞机着陆时的放电时间常数及某型飞机2种不同状态下的飞机电容:空中飞行时400pF,停靠地面时1.3nF。电荷分布计算结果与理论分析吻合,电容值与美军标Mil-Std-464给定数值一致,说明计算正确。最后根据静电放电的脉冲特性,建立了着陆时的静电放电的传输线电路模型,通过分析模型,给出了着陆时高阻的安全放置位置。     

Applications of electrostatic stretch-and-positioning of DNA

The authors have previously reported that the electrostatic orientation and the dielectrophoresis (DEP) of DNA occur under ≈1 MHz, >1×10⁶ V/m field, by which DNA strands are stretched straight along field lines and positioned onto electrode edges. This paper presents some application of this stretch-and-positioning method to genetic engineering. It is shown that the DNA size distribution, as well as the activities of nuclease, can be determined by the measurement of the apparent length of stretched DNA. Several methods are developed to immobilize stretched DNA onto a substrate, including: (1) immobilization onto a conducting substrate for observations with the scanning tunneling microscopy, (2) anchoring onto a substrate only at both ends of the DNA using special electrode configuration, and/or molecular binding between avidin and biotin. The DNA can be held without contact to the substrate in the latter method, so that it does not cause steric hindrances to the DNA-binding enzymes. A novel fluid integrated circuit (FIC) device is proposed in which stretched DNA is cut by laser beam for the successive sequencing. A method to obtain unidirectionally oriented DNA is developed. The spatial resolution, and the small number of molecules required, are the advantages of the assays and measurements using electrostatic DNA manipulations over conventional biochemical methods. It is hoped that the methods may open a way to a novel category of “molecular biochemistry with spatial resolution.”     

Charging characteristics on dielectric surface by differentcharging processes in vacuum

This paper describes charging characteristics on a dielectric surface in vacuum by electron irradiation and field emission by a triple junction under negative and positive DC HV applications. The authors measured the 2-D distribution of electrostatic charging on a dielectric surface in situ. Experimental results revealed that the negative charge distribution caused by the electron beam had a conical shape over the whole surface. On the other hand, for a triple junction, it was an acute distribution around the triple junction. Moreover, they quantitatively investigated the difference of the 2-D charging distribution, using certain shape parameters, between the two charging processes mentioned above. In addition, they examined the time decay characteristics of the surface potential on the dielectric in vacuum