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     

Dynamic electric fields computed by finite elements

The authors describe how the MSC/MAGNETIC finite-element analysis program is used to compute electrostatic and electrodynamic fields. Example calculations are described for a capacitor with multiple lossy dielectric layers and for a high voltage bushing with a resistive coating. Comparison with classical results is given for the capacitor. The results for the simple lossy capacitor agree with conventional circuit theory. The results for the conductively coated bushing appear to show correctly the influence of conductivity on AC electric fields     

Sterilization of liquid foods by pulsed electric fields

Recent advances in the field of high-voltage pulse power technology have provided scope for the development of nonthermal sterilization methods free from the disadvantages commonly encountered with existing physical, chemical, or radiation sterilization. The flexibility allowed in the application of electrical energy can make high-field sterilization economical, compact, energy efficient, and environmentally acceptable. The main thrust of present research in this field is the application of high-field electric pulse technology to kill microorganisms in a manner consistent with development of industrial scale nonthermal sterilization methods     

Inactivation of microorganisms by pulsed electric fields ofdifferent voltage waveforms

Processing foods with HV pulsed electric fields (PEF) is a new technology to inactivate microorganisms and denature enzymes with only a small increase in temperature. Introduction of this new technology will replace or complement conventional thermal processing methods. It will also provide consumers with safe, nutritious foods with fresh quality. For a given peak value of field intensity and amount of electric energy input, PEF inactivation of microorganisms is closely related to the waveform of applied pulses. Inactivation of microorganisms was studied with different waveshapes including exponential decay, oscillatory decay, square waves, and bipolar pulses. Microbial inactivation was tested in a parallel-plate static treatment chamber. Treatment field intensity ranged from 12 to 40 kV/cm while pulse length ranged from 30 to 180 μs. From the microbial test results, bipolar square-wave pulses are the most efficient in terms of microbial inactivation for commercial PEF pasteurization     

Ways to calculate electric fields in traction electric motor insulation by equivalent charge method

A procedure permitting one to calculate the electric fields in multilayer insulation based on the equivalent charge method is presented. Consideration of the new algorithm shows its fast response and proper accuracy.     

Mobility and high electric fields

Although the mobility constant of an ionic species can be easily measured at low electric potentials, at high potentials the constant often appears to be dependent on the potential or apparent electric field. Clearly, if the mobility varies with the applied potential, then the concept of a mobility constant becomes ambiguous. This paper examines the assumptions normally made to convert raw data to a mobility. The examination shows the ambiguity arises when the space-charge effect is ignored in the analysis at high potentials, Using the charge-injection equation, the result shows the mobility at high electric fields can still be considered a constant. The analysis predicts the nonlinear rise in the measured current density at high field, without the need to impose a nonconstant mobility. Conversely, the result shows the true mobility can be obtained by extrapolating the apparent mobility to zero electric field     

电蓄热水地暖系统

随着采暖费由职工单位缴纳改为单位补贴个人缴纳制度改革的深入,尤其是即将实行的集中供热采暖按量收费、节约归己、不足自补制度之后,人们对建筑节能的关注度日益提高。选用节约型的采暖方式,已渐成为建房和购房者的热点之一,故有必要对一些采暖方式作出分析与比较,以资参考。现将电蓄热水地热采暖技术简述如下。     

Rate of charging of spherical particles by monopolar ions in electric fields

This paper presents a numerical algorithm to simulate the charging dynamics of high-resistivity spherical particles by the ionic bombardment in an electric field. The algorithm is based on solving the Poisson equation, governing the electric field distribution, and the differential equation expressing the charge conservation law. The Poisson equation is solved be means of the finite-element method using the triangular discretization and the first of interpolation. The finite-volume method (in a version called the donor-cell method) is used to handle the charge conservation equation. Results of simulation are also presented and they illustrate the effect of different parameters on the charging dynamics. For high-conductivity particles, the charging rate is practically identical to that given by the Pauthernier formula. Charging of high-resistivity particles leads to more complicated solutions and is much slower.     

Intracellular DNA damage induced by non-thermal, intense narrowband electric fields

Intracellular DNA damages caused by intense burst sinusoidal electric fields (IBSEFs) were investigated by means of an alkaline comet assay method. Non-thermal, 200 ?s-long IBSEF with various frequency values (300 kHz-100MHz) and strengths (up to 200 kV/m) was applied to Chinese hamster ovary (CHO) cells in a suspending medium between 1 mm gap parallel electrodes. The comet assay suggests that 100 kV/m IBSEF with frequencies exceeding 1 MHz or 100 MHz IBSEFs with field strengths exceeding 3 kV/m induces significant DNA damage. According to the numerical calculation of the electric field over a simplified cell model under an alternating electric field, the intracellular field strength increases with increasing alternating frequency. The minimum level of the field strength that induces the DNA damage is in the range of 10-30 kV/m. This intracellular strong field might trigger biological processes leading to the DNA damage.     

Modeling of conductive particle behavior in insulating fluidsaffected by DC electric fields

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, or biological cell manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids by means of relatively high DC electric fields. This paper is aimed at characterizing the behavior of such particles by numerical modeling of two aspects: (1) particle motion under the action of electric field forces and (2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behavior are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impact with the electrodes. The conclusions regarding the behavior of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment     

Can water cause brittle fracture failures of composite non-ceramic insulators in the absence of electric fields?

It was postulated by J. Montesinos et al. (see ibid., vol.9, p.236-43, 2002), based on experimental evidence, that brittle fracture failures of composite (non-ceramic) HV insulators could be caused by water and mechanical stresses. It was also claimed therein that the brittle fracture process was more likely to happen with water than acids. This postulation could be of major importance as its ramifications might affect the entire composite insulator technology and, in particular, the usage of glass fiber polymer matrix composites in HV applications. Such an important statement should not be left without an independent verification. Therefore, attempts have been made in this research to initiate this process in unidirectional E-glass/modified polyester and E-glass/vinyl ester composites, used in non-ceramic insulators, by subjecting them to water under four-point bending conditions. This was done to independently verify the main conclusion of J. Montesinos et al. that water may be more damaging to unidirectional E-glass/polymer composites than acids. It has been clearly shown in this work that water, in the absence of electrical field, cannot cause stress corrosion cracking of unidirectional E-glass/polymer composites and thus brittle fracture of composite non-ceramic insulators. Thus the main results of J. Montesinos et al. could not be independently reproduced.     

Influence of temperature and water on the breakdown electric field strength of XLPE cables under divergent fields

The present paper introduces experimental results on treeing breakdown phenomena in actual power cables. Using a water capillary electrode, cable samples immersed in silicone oil have been tested by alternating (50 Hz) and direct voltage stresses. Examination of the needle geometrical breakdown electric field strength resulted in a detailed analysis of the influence of temperature and the presence of water on the breakdown of XLPE cables under divergent fields.     

Particle patterning using fluidics and electric fields

Electric-field manipulation of micro-particles in suspension can create patterns via a number of particle forces and fluid flows. These effects are assessed for their suitability for down-scaling to form nano-patterns such as may be incorporated into structured nano-composites. Consideration is given not only to the assembly of field-aligned chains or wires, but also to methods that can give cross-field assembly and even 2-D patterns or crystals. Dielectrophoresis is often the dominant driving force behind particle assembly, but other dipole-dipole interactions and also electrically-driven fluid flows are increasingly recognized as significant or dominant. Orientation of non-spherical particles in frequency-selectable directions is also possible. Estimates for the threshold field strengths required for using these effects to handle nano-particles are considered. Finally the use of media with modified permittivity to increase the field-induced forces or to optimize the selectivity of particle incorporation is discussed.     

Charging of one or several cylindrical particles by monopolar ions in electric fields

In many electrostatic processes (precipitation of dust, separation of granular mixtures, spraying of powders) insulating particles are subjected to unipolar charging in the presence of other bodies. The present paper addresses this problem from both a computational and an experimental point of view, with the aim to extend an original numerical method of unipolar charge computation to the case of two or more particles, relatively close to each other. The charge acquired by cylinders of various dielectric constants was evaluated with a computer program based on the boundary element method of field analysis. The experimental setup simulated the charging conditions of millimeter-size calibrated cylinders of polyvinyl chloride in a roll-type electrostatic separator, the unipolar space charge being generated by a wire-type electrode. The experimental results, which were in good agreement with the theoretical predictions, put forward that the relative spacing between the particles changes the value of the saturation charge, an effect, which is stronger for particles of higher dielectric constant. These facts should be taken into account in the design of any electrostatic technology based on the corona charging of granular matter.     

Interaction forces of dielectric cylinders in electric fields

The electric field configuration and forces in a dielectric system of two long circular cylindrical bodies is studied in detail. The cylinders are parallel to each other and situated in a uniform transverse electric field. The cylinder bodies and surrounding medium have arbitrary and different permittivities. The origin of the forces in the piecewise-homogeneous material under study is polarization in the dielectrics. The local forces on the surfaces of the cylinders are examined. It is shown that the cylinders exert forces on each other. The total forces and torques depend on the dielectric materials, the geometric parameters of the system, and the orientation of the applied electric field. Under these conditions the problem has a complete analytic solution     

Bacterial decontamination of liquids with pulsed electric fields

The effect of pulsed electric fields on the viability of microorganisms, mainly bacteria, in liquids has been studied since the 1960's. Experimental results obtained over a large range of electrical and microbiological parameters, point towards an irreversible formation of pores in the cell membrane as the mechanism for lysing. The model of membrane pore formation seems to fail only for ultrashort electrical pulses, where intracellular effects, and possibly resonant effects, might dominate. This paper presents an overview of the effect of pulsed electric fields on the viability of microorganisms in liquids, In particular, the lytic effect of variations in the electrical pulse parameters, such as pulse shape, amplitude, duration, and single shot vs. repetitive operation, is described, A major application of the pulsed electric field method is `cold' bacterial decontamination of liquid food and drinking water. The energy consumption for complete bacterial decontamination is presently 100 to 400 kJ/l. A possible reduction of the required energy by utilizing intracellular electric field interactions and resonance effects is discussed     

Biological effects of narrow band pulsed electric fields

This paper describes the process of narrow band pulsed electric fields (NPEFs) and its effect on mammalian cells. The NPEF consists of a pulse modulated sinusoidal wave (PMSW), which allows delivery of well-defined electric fields in terms of frequency, field strength and deposition energy to the biological systems. 100 mus long sinusoidal electric fields with a frequency of 0.02, 2 or 50 MHz and field strengths of up to 2 kV/cm are applied to CHO cells with variation in the DNA density in the cells investigated by means of Acridine Orange assay. The experiments indicate that 50 MHz fields cause DNA degradation without cell membrane defects, while 0.02 MHz fields lead to an increase in membrane permeability which is similar to the effect known as electroporation. The intermediate frequency of 2 MHz influences both the membrane and DNA. It is demonstrated that the MHz range narrowband electric fields with the amplitude level of 1 kV/cm cause intracellular effects in mammalian cells.     

Several effects of electric fields on liquid extraction

The effects of electric fields on dispersed liquid-phase flow behavior and mass transfer efficiency have been investigated for several liquid-liquid systems using single/multiple-nozzle extraction columns. Drop size, drop surface charge density, and drop terminal velocity were correlated with the applied field strength by typical models. Drop surface area and velocity were increased significantly by the electric fields. The end effects were separated from the overall mass transfer process by varying the plate gap. The mass transfer coefficients for drop freefall region were calculated. The overall extraction efficiencies increased 51% for heptane-furfural and 24% for the toluene-water-methanol system