High Voltage Electrical Discharges Research Articles

High-voltage electrical discharges induced by an ultrashort-pulse UV laser system

Using a femtosecond UV laser source (248.6 nm), we have conducted studies on large-gap laser-induced electrical discharges. Parameters such as pressure, lens selection, focal position and laser energy were investigated. We also present an experimental technique that allows the measurement of ionization cross-sections at atmospheric pressures. Spectroscopic analysis of the laser plasma and discharge are also presented. Prospects and conditions leading to a discharge over tens of metres, with dual UV and IR laser pulses, are discussed.

Optimization of a continuous pulsed corona reactor

Pulsed corona discharge processes utilize chemical radicals, ions, and highly reactive molecules produced from a high-voltage pulsed electrical discharge. Recently, these processes have been used for treating organic contaminants in wastewater. The chemistry induced by the pulsed streamer corona in the aqueous phase involves several reactions and is based on hydrogen peroxide. The principal objective of this work is to minimize the amount of hydrogen peroxide needed in a plug-flow reactor to degrade phenol to a prespecified level. A simplified model of the corona reactor is utilized in conjunction with dynamic optimization. Scaling analysis and quasi-steady-state assumptions are used to derive analytical expressions for calculating the optimal hydrogen peroxide concentration profile. Simulations are performed to verify the performance of this optimization strategy.

Raman Study of the Pulsed Discharge Effect on Molecular Relaxation in Aqueous Sodium Nitrate

The high-voltage pulsed electric discharge effect (HPED activation) on the Raman spectra of a saturated aqueous solution of sodium nitrate (NaNO3/H2O) in the region of the totally symmetric vibration ν1(A) of the NO-3 anion has been studied. The temperature dependences of the width and frequency of the corresponding spectral line are examined.

An electrohydraulic installation

An installation using the electrohydraulic effect is designed for investigation of physicochemical processes running in liquids under the action of high-voltage electric discharges. A control unit allows one to vary the discharge voltage (from 1 to 40 kV), current (10–150 kA) duration of the discharge pulse (from 0.3 to 2 μs), and the pulse repetition rate (from 0.1 to 10 Hz).

Preservation: past, present and future.

Foods deteriorate in quality due to a wide range of reactions including some that are physical, some that are chemical, some enzymic and some microbiological. The various forms of spoilage and food poisoning caused by micro-organisms are preventable to a large degree by a number of preservation techniques, most of which act by preventing or slowing microbial growth. These include freezing, chilling, drying, curing, conserving, vacuum packing, modified atmosphere packing, acidifying, fermenting, and adding preservatives. In contrast, a smaller number of techniques act by inactivating micro-organisms, predominantly heating (pasteurization and sterilization). Complementary techniques restrict access of micro-organisms to food products, e.g. aseptic processing and packaging. New and 'emerging' preservation techniques include more that act by inactivation. They include the application of ionizing radiation, high hydrostatic pressure, high voltage electric discharges, high intensity light, ultrasonication in combination with heat and slightly raised pressure ('manothermosonication'), and the addition to foods of bacteriolytic enzymes, bacteriocins, and other naturally-occurring antimicrobials. Major trends, reacting to consumers' needs, are towards the use of procedures that deliver food products that are less 'heavily' preserved, higher quality, more convenient, more 'natural', freer from additives, nutritionally healthier, and still with high assurance of microbiological safety.

Mathematical modeling and interpretation of reactive plasma chemistry

A problem of much recent technological interest is the analysis and interpretation of the chemistry of audiofrequency plasma enhanced chemical vapor deposition of thin films. In this process, low pressure methane gas is input into a reactor chamber and a low-current, high-voltage audiofrequency electric discharge applied. The energetic electrons thus produced bombard the methane molecules, fragmenting them, and causing radical and ion formation. These new species go on to form a range of products under various operating conditions from soot-like amorphous carbon, to diamond-like carbon. Despite the increasing experimental understanding of reactive organic plasma dynamics, the chemical kinetics of the reactions in the gas phase is still not completely understood: quite different species densities are found in different regions of the discharge system implying spatially inhomogeneous physiochemical processes. The experimental problem is first outlined, and a simple physiochemically-motivated reaction-advection-diffusion model of the reactive plasma chemistry described. Results of the kinetics models are presented and discussed in terms of the input model parameters and related to surface deposition.

Design considerations for a CCFL and its surroundings

Abstract— A TFT‐LCD module includes a backlight unit, which normally uses one or more thin cold‐cathode fluorescent lamps (CCFLs). Since a CCFL is driven at high frequency and high voltage, there is a leakage current. In recent years, TFT‐LCD modules have been getting thinner, with a wider screen size and a narrower frame; consequently, the leakage current has come to have a significant influence on the design of the LCD module and the dc/ac inverter unit that generates the high‐voltage ac to drive the CCFL. It is actually impossible to probe the inside of a working CCFL because of the high voltage, high frequency, and low electric discharge current. This fact adds to the difficulty of the analysis and the design. This paper proposes an electrical model of a CCFL and a simulation method using the model, making it possible to analyze the inside of the CCFL and to provide some important parameters that are required for the basic design of the LCD module and the dc/ac inverter, before the construction and measurement of actual samples.

Nonlinear physical characteristics of a high-voltage electric discharge in a two-phase liquid

Physical features of an electric discharge in a gas-liquid medium are investigated; a direct relationship between the entropy change and the fractal nature of the medium itself is shown. Simplified equations and laws of conservation that describe the dynamics of the electric discharge in the two-phase liquid with allowance for the thermodynamic properties of the medium as functions of its fractal structure are used.

Aqueous-phase pulsed streamer corona reactor using suspended activated carbon particles for phenol oxidation: model-data comparison

A pulsed high-voltage electrical discharge that produces streamers, or regions of non-thermal plasma, has been shown to be useful for degrading small organic species in synthetic wastewater in a bench-scale experimental system. This process is an example of an advanced oxidation technology that leads to the formation of hydroxyl radicals, hydrogen peroxide, and aqueous electrons, which in turn lead to organic contaminant removal through direct chemical reactions. Experimental results show that with activated carbon particles present, the removal of organic contaminants is increased due to the combination of direct oxidation of the organic species in the bulk fluid by pulsed corona and adsorption of the organic species to the surface of the activated carbon. There exists also the possibility of reactions occurring on the surface of the activated carbon-induced by the electrical discharge, thus continually regenerating the activated carbon. The present study develops a mathematical model incorporating multicomponent bulk and surface phase reactions coupled with mass transfer, internal particle diffusion, and adsorption to the carbon particles. Comparison of experimental results and theory using phenol as a model compound implies surface reactions occurring on the activated carbon particles.

Zirconium boride and tantalum carbide coatings sprayed by electrothermal explosion of powders

Refractory zirconium diboride and tantalum monocarbide ceramic powders were sprayed using an electrothermal explosion caused by a high-voltage electric breakdown and large-current discharge heating. This spray technique was improved using a purpose-designed powder container, which made it possible to melt the powder completely and accelerate it to impinge on substrates. The electrical energy applied to the powder was estimated to be about twice the energy theoretically needed to melt just the powder. Although the ceramics used in this work are hard-sintered materials by nature, they could be sprayed and deposited to form coatings on metal substrates without additives and sintering agents. The coatings formed exhibited no chemical decomposition in the boride, and only small amounts of decarburization in the carbide due to its nonstoichiometry. The tantalum carbide coating mixed with iron and aluminum substrates in the range of 10 μm to several tens of micrometers.

Analytic relations between the parameters of a high-voltage discharge channel plasma in a liquid and a plasma jet in an evacuated chamber

Analytic relations are derived between the parameters of a high-voltage electric discharge plasma in a liquid and the parameters of a plasma jet in an evacuated chamber. These relations can be used to calculate the plasma temperature and pressure in the axial zone of the discharge channel by using the experimentally measured temperature of the plasma jet and its geometric characteristics.

Some features of the hydrodynamic characteristics of a high-voltage electric discharge in a liquid with a two-pulse power deposition law

An analysis is made of the external hydrodynamic problem of an underwater electric discharge with a two-pulse power deposition law in the channel. As a result of an analytic solution of the problem, it is shown that the pressure function at the channel wall is a series of pulses of decaying amplitude, while the pressure function for a fixed point in the wave field is a series of increasing pulses.

Spatially Resolved NMR Spin Diffusion in Solid Polymers

Measurements of the spatial distribution of microscopic domain sizes are reported using spatially resolved1H NMR spin diffusion in solid polymers. Microscopic space encoding for spin diffusion is achieved for two classes of polymers with dynamic heterogeneities by use of the dipolar filter. Macroscopic space is resolved by phase-encoded magic-echo imaging using1H NMR. Spatial changes of the average domain sizes are detected for diblock polymer poly(styrene-b-isoprene) and poly(ethylene oxide) phantoms. As a first application of this new method, changes in microscopic domain sizes due to high-voltage electrical discharge are imaged in low-density polyethylene cable-insulator material.

Design and characterization of a shock wave generator using canalized electrical discharge: Application to lithotripsy

During recent years, much work has focused on breaking urinary and biliary stones using extracorporeal shock wave devices. Up to now, in terms of fragmentation efficacy, the ‘‘electrohydraulic’’ principle is the gold standard. In an electrohydraulic shock wave generator, a plasma is created by a high-voltage electrical discharge between two underwater electrodes. This kind of shock wave generator has a significant drawback because of the large variations of pressure pulses. Moreover, the wear of the electrodes is considerable, leading to nonconstant electrical discharge conditions all along the treatment. A new method to canalize the plasma between the electrodes, using highly conductive liquid, was investigated. Based on this principle a new spark plug was designed. This paper deals with the description and the characterization of this new type of spark plug. The electrical and geometrical parameters are presented. Measurements of the focal point pressure amplitude, of the spatial pressure distribution using different voltage settings, are reported. The acoustic energy in the focal zone is computed. We show that using this principle, the wear of the electrodes has been tremendously reduced. A comparison of in vitro results with other shock wave technologies shows that this new spark plug represents a significant breakthrough in terms of stone fragmentation efficacy. This spark plug is not only useful in the medical field, but it should also be of great interest to laboratories.

Studies on signal transduction mechanisms for adrenaline-driven lipolysis in white and brown adipocytes

White and brown rat adipocytes have been permeabilised by repeated exposure of the cells in suspension to high voltage electrical discharges. The resulting preparations were permeable to low molecular weight materials, e.g., cyclic AMP, propidium iodide, and were stable in suspension with little evidence of rapid resealing, or of gross damage to the cell membrane. Leakage of lactate dehydrogenase was not markedly enhanced except at voltages in excess of 2 kV cm −1 for brown adipocytes. Exogenously-added cyclic AMP stimulated lipolysis (measured as glycerol release) in the electropermeabilised adipocytes far more effectively than in intact adipocytes. In brown, but not in white, adipocytes this effect was enhanced by addition of millimolar ATP. The EC 50 for stimulation of glycerol release by cyclic AMP was 0.2 μM in electropermeabilised brown adipocytes, and 2 μM and 40 μM in electropermeabilised white adipocytes obtained from weanling and adult rats respectively. The effect of cyclic AMP on lipolysis was enhanced by addition of an inhibitor of cyclic AMP phosphodiesterases and was reduced by addition of 5′-AMP, adenosine or inosine (in brown adipocytes). Addition of adenosine deaminase caused a small, but significant, enhancement of cyclic AMP-driven lipolysis. Catecholamine-driven lipolysis was observed in electropermeabilised brown and white adipocytes, especially in the presence of GTP. Adrenaline-, and to a lesser extent cyclic AMP-, driven lipolysis in electropermeabilised white adipocytes was inhibited by insulin. This effect of insulin was not enhanced by addition of GTP or of a metabolically stable GTP analogue. The results obtained establish the electropermeabilised preparation as suitable for analysis of signal transduction pathways in white and brown adipocytes.

Fourier Transform Infrared Emission and Rotational Spectra of the X2Σ + States of SrH and SrD

The vibration-rotation spectrum of the 2Σ + ground state of strontium monohydride has been recorded in emission using a Fourier transform spectrometer. The rotational spectra of SrH and SrD have also been measured between 200 and 450 GHz using an absorption spectrometer. The gas-phase free radicals have been produced in a ceramic furnace by the reaction of elemental strontium with molecular hydrogen or deuterium in the presence of a high-voltage electrical discharge. The molecular constants including the rotational constant, centrifugal distortion constants, spin-rotation constants, and magnetic hyperline interaction constants have been determined from the spectra.

Formation of PAHs and C 60 as intermediates in the carbonization of liquid benzene and toluene upon the effect of electric discharges

Upon the effect of high-voltage electric discharges in benzene, toluene, and other aromatic liquids, carbonization occurs, and different PAHs and C 60 are formed as intermediates. The distribution and time profile of the PAHs depend on the initial substance and on the “inert” gas (N 2, Ar, CO 2) applied.

Effects of Repeated Exposure to High-Voltage Electric Discharges and Low-Frequency Electromagnetic Fields on Cultured Mouse P3×63Ag8 Plasmocytoma Cells

When cells of the mouse plasmocytoma P3x63Ag8 were repeatedly exposed to high-voltage electric discharges (1.34 KV/cm, 1 sec between pulses; time constant, 25 μsec), they fused into multinuclear cells. Using the same procedure, myeloma cells were induced to form heterokarions by fusion with human or mouse lymphocytes, and to internalize formaldehyde-treated erythrocytes. Under optimal conditions, cells were fused extensively without substantial loss. Exposure of the cells to low-frequency (50 Hz) sinusoidal electromagnetic fields (magnetic field amplitude of 200 μT) did not appear to perturb membrane substructures in such a way as to influence the fusogenic effect induced in high electric fields.

Bacterial genetics by electric shock

Subjecting bacteria to a high-voltage electric discharge renders the cells permeable to DNA. This powerful method allows the genetic manipulation of bacterial species that cannot easily be transformed by conventional techniques.

The study of the process of dioxydifluoride synthesis in the temperature range of 135 - 173 K

The interaction of atomic fluorine produced by fluorine molecules dissociation with high-voltage electric discharge with oxygen in all studied temperature range was accompanied with the formation of dioxydifluoride. It was found that at the given temperature, oxygen content and total gas pressure, the observed rate of dioxydifluoride formation is determined by the gas cooling time to the experimental temperature and by the intensity of fluorine atoms flow at the exit end of the discharge tube. The character of dependences of the observed rate of dioxydifluoride formation on the oxygen partial pressure and total gas pressure greatly depends on the time of gas cooling. The fraction of atomic fluorine involved in the process of dioxydifluoride synthesis is determined by the temperature and the time of gas cooling, and this fraction is increased the decrease of these parameters and equals to unity at T=77 K and T <10 s. The main role in the process of dioxydifluoride formation is played by the reaction: O2F + F + M - → O2F2 + M where M=F2, O2F, O2, F, is a wall.