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The two-dimensional electroconvection between two plates has been studied from the theoretical and numerical point of view. However, the stability of the finite amplitude solution is an open theoretical problem. Here we use two sets of numerical techniques to analyze this problem. On one hand, particle-in-cell techniques for simulating the charge distribution combined with finite elements for computing...
As a part of a study of electrocoalescence of water droplets in oil, the controlled generation of small drops (diameter ~ 100 mum) is considered. The technique used consists in applying a voltage pulse promoting the deformation of a meniscus at the end of a capillary tube through the action of electric forces. For pulses of short enough duration, the transient deformation can lead to the ejection...
This paper is aimed at the influence of hydrostatic pressure on the morphology and final length of creeping discharges propagating over solid / liquid insulating surfaces in a point-plane electrode arrangement submitted to lightning impulse voltages. Three types of solid insulators (namely polycarbonate, phenoplast resin (Bakelite) and glass), immersed in mineral oil are tested. It is shown that the...
The paper presents streaming current distributions measured in an overflow system in both laminar and turbulent conditions. These distributions were taken using a shifting spherical electrode connected with electrometer. For lower values of Reynolds number the profile of current is parabolic. For higher values of Reynolds number the profile is flattened. In this paper also charge density distributions...
This paper deals with the Quincke rotation of small particles. It is usual to explain this DC electorotation looking at the action of the free charges present in the liquid which under the application of an electric field accumulate at the surface of the insulating object. Then it acquires a dipole moment in the direction opposite to that of the field. In turn the particle begins to rotate in order...
In these terms we show the results of computer modeling of symmetric and non-symmetric EHD flow in symmetric wire-wire electrode system. This problem was solved in Ansys and ComsolMultyphysics programs. We develop computer modeling of EHD flow algorithm in stationary variant which helps us to solve wide area of electrohydrodynamic problems. We researched a new type of charge diffusion and saw a disruption...
An experimental investigation has been conducted to study a fundamental electrohydraulic discharge characteristics and plasma parameters in a dielectric liquid solution with Ar gas injections. HF-bipolar high voltage was supplied to the converging angle type plate electrodes with 1 mm gap distance inside dodecane with conductive salt solutions. Experiments are conducted for Ar gas flow rate from 0...
A study was conducted to assess the effectiveness of pulsed electric field (PEF) inactivation of a heterogeneous community of microbes in milk over electric field strength of 10 - 40 kV/cm and 10 to 120 pulses per millilitre. High electric field strength and pulse number decreased microbial growth but inoculum-size affected PEF effectiveness when only a few pulses were applied. The composition of...
Aging of oil-paper insulation was investigated under controlled laboratory conditions. Traditional and modern diagnostic tools and techniques are discussed. Insulation condition testing includes common chemical diagnostics such as acidity tests and several new chemical techniques such as determination of relative content of dissolved decay products by spectrophotometry, solid suspension by turbidimetry,...
This paper reports on the initiation and propagation of streamers in synthetic ester and silicon oils for power transformers. The study is carried out under dc voltage using a point-plane electrode arrangement. We especially analyze the initiation voltage of streamers as well as the associated current and light emitted by these streamers. The influence of hydrostatic pressure (PH) on these characteristic...
Homodyne detection of light scattered by a colloidal suspension is a well known method of determining the size of the colloidal particles. Heterodyne detection is achieved when the scattered beam interferes with the incident beam on the detector. Heterodyne detection can be used to measure the average velocity of the particles in the suspension. In this paper we present measurements of the electrophoretic...
In this study the effect of microorganism size and shape on the killing efficiency of pulsed electric field is investigated both experimentally and using a transient finite element program. The effect of cell size, membrane thickness, cell shape (spherical, elliptical and cylindrical) on the trans-membrane voltage is studied. It has been found that both the cell size and cell membrane thickness have...
Kinetics of transient photocurrents caused by dissociation of exciplexes, intermediate excited states, into the geminate pairs of solvent-separated radical ions A- + D+ is computed in the case that the diffusion separation time of the ion pair is comparable to the life time of exciplexes, precursors of the ions. The time dependence of the displacement current of the ion pairs A- + D+ was found from...
It is well known that an isothermal dielectric liquid can be driven by electroconvection. It has been demonstrated that two phenomena could generate space charge in isothermal dielectric liquids and then induce a fluid movement. These two electroconvective effects are bulk conduction and ion injection. In order to improve the performance of electroconvective devices, the velocity of the flows must...
This paper describes the experimental results on the creeping streamer progressing the surface of a bakelite board immersed in transformer oil under the application of a standard lightning impulse voltage with peak values of plusmn100~350 kV. The growth of streamers is significantly affected by the thickness of bakelite board and the streamers are extended longer exponentially for the applied voltage...
The valuable information about the nature and strength of interactions in liquid solutions, over a range of mole fractions, can be obtained using dielectric studies. A large amount of investigation has been carried out in recent years on the dielectric measurements of polar solutions with various molecular structure and different functional groups, in order to understand and provide further information...
Pulsed arc electrohydraulic discharge process (PAED) has been studied for the removal of some of organic pollutants. Firstly, the destruction of para-chlorophenol by PAED system was studied under some different experimental conditions (ionic strength, pH, conductivity and organic initial concentration) in a 5.6-L reactor with the following configuration: 2.9 kV of potential, 140 muF of capacitors...
Dielectric response of oil impregnated kraft paper has been measured in the frequency range 8 Hz to 2 MHz in a custom designed test cell. Temperature was varied between -17 and 60degC, allowing master curves for 20degC condition to be established for the frequency range 10 mHz to 10 MHz. Paper types and moisture was varied. The dielectric response showed losses in the low frequency region dominated...
We have developed a new vegetable based insulating oil for transformers called PFAE (palm fatty acid ester). PFAE has 0.6 times less viscosity and a 1.3 times higher dielectric constant compared to mineral oil. This means that a PFAE-immersed transformer has better cooling efficiency and better insulation characteristics in paper-and-oil composite insulation systems, resulting in size reduction in...
The time domain reflectometry is a relatively recent technique which in general allows impedance measurement of a coaxial air line portion filled with the device under test (DUT). Basically the system is a closed circuit RADAR implying an incidental step pulse and its feedback that is a time reflected signal. When the studied material is dielectric matter, most of its electric properties are contained...
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