Showing papers on "Electric discharge published in 2006"

A finite element model of EDM based on the Joule effect

Abstract: A thermal–electrical model was developed for sparks generated by electrical discharge in a liquid media. A cylindrical shape has been used for the discharge channel created between the electrodes. The discharge channel being an electrical conductor will dissipate heat, which can be explained by the Joule heating effect. The amount of heat dissipated varies with the thermal–physical properties of the conductor; as a result, the maximum temperature reached is different. In the present model, the radii value of the conductor is a function of the current intensity and pulse duration. The thermal–physical values used in the model are the average of both the ambient and melting value. Copper and iron are the materials used for anode and cathode, respectively. The Finite Element Analysis (FEA) results were compared with the experimental values of the table of AGIE SIT used by other researchers [D.D. DiBitonto, P.T. Eubank, M.R. Patel, M.A. Barrufet, Theoretical models of the electrical discharge machining process—I: a simple cathode erosion model, Journal of Applied Physics, 66(9) (1989) 4095–4103; M.R. Patel, M.A. Barrufet, P.T. Eubank, D.D. DiBitonto, Theoretical models of the electrical discharge machining process—II: the anode erosion model, Journal of Applied Physics, 66(9) (1989) 4104–4111; P.T. Eubank, M.R. Patel, M.A. Barrufet, B. Bozkurt, Theoretical models of the electrical discharge machining process—III: the variable mass, cylindrical plasma model, Journal of Applied Physics, 73(11) (1993) 7900–7909]. In order to show the universality of the model it was obtained results for all current intensity values of the table. The Tool Wear Ratio (TWR) and Material Removal Rate (MRR) as well as surface roughness results agree reasonably well with the researcher's values found for that table and itself.

Development of subsonic electrical discharges in water and measurements of the associated pressure waves

Abstract: This paper first presents an experimental electrical and optical study of the development of an electrical discharge in water. The point–plane water gap is subjected to a 0.02 µs/350 µs impulse voltage. A Schlieren device associated with an image converter or a photomultiplier demonstrates that the discharge phenomenon requires heating of the water located around the extremity of the point. This thermal process leads to the formation of gas bubbles in which an electrical discharge propagates. In the experimental conditions a threshold value of 80 J is necessary to create bubbles. No UV or IR light emission is recorded before the presence of bubbles is detected. When the energy conditions are sufficient (≥200 J), the volume of bubbles grows until the whole inter-electrode space is filled; then a breakdown of the gap occurs. When this happens, a high amplitude pressure shock wave is generated. In the second phase of this work the shock wave created by the gap breakdown was studied for energy levels up to 100 kJ. It is clearly pointed out that the pressure shock wave peak value depends on the energy remaining at breakdown time. For a constant remaining energy, the peak pressure value increases with increasing gap length.

Plasma-Assisted Combustion of Gaseous Fuel in Supersonic Duct

Abstract: The field of plasma-induced ignition and plasma-assisted combustion in high-speed flow is under consideration. Nonequilibrium, unsteady, and nonuniform modes are analyzed as the most promising in reducing a required extra power. Numerical simulations of uniform, nonequilibrium, continuous, and pulse discharge effect on the premixed hydrogen and ethylene-air mixtures in supersonic flow demonstrate an advantage of such a technique over heating. At the same time, the energetic price occurs rather large to be scheme practical. A reduction of the required power deposition and mixing intensification in nonpremixed flow could be achieved by nonuniform electrical discharges. Experimental results on multielectrode discharge maintenance behind wallstep and in the cavity of supersonic flow are presented. The model test on hydrogen and ethylene ignition is demonstrated at direct fuel injection

Vacuum arc deposition devices

Abstract: The vacuum arc is a high-current, low-voltage electrical discharge which produces a plasma consisting of vaporized and ionized electrode material. In the most common cathodic arc deposition systems, the arc concentrates at minute cathode spots on the cathode surface and the plasma is emitted as a hypersonic jet, with some degree of contamination by molten droplets [known as macroparticles (MPs)] of the cathode material. In vacuum arc deposition systems, the location and motion of the cathode spots are confined to desired surfaces by an applied magnetic field and shields around undesired surfaces. Substrates are mounted on a holder so that they intercept some portion of the plasma jet. The substrate often provides for negative bias to control the energy of depositing ions and heating or cooling to control the substrate temperature. In some systems, a magnetic field is used to guide the plasma around an obstacle which blocks the MPs. These elements are integrated with a deposition chamber, cooling, vacuum gauges and pumps, and power supplies to produce a vacuum arc deposition system.

A semi-empirical approach for residual stresses in electric discharge machining (EDM)

Abstract: High residual stresses are developed on the surfaces of electric discharge machined parts. In this study, layer removal method is used to measure the residual stress profile as a function of depth beneath the surface caused by die sinking type EDM. Cracking and its consequences on residual stresses are also studied on samples machined at long pulse durations. A modified empirical equation is developed for scaling residual stresses in machined surfaces with respect to operating conditions. In this model, a unit amplitude shape function representing change in curvature with respect to removal depth is proposed. The proposed form is found to be a special form of a Gauss Distribution. It is the sum of two Gaussian peaks, with the same amplitude and pulse width but opposite center location. The form can be represented by three constant coefficients. These coefficients depend on the released energy by a power function.

Efficiency of the shock wave generation caused by underwater electrical wire explosion

Abstract: Shearing interferometry, together with shadowgraph and Schlieren photography techniques, has been applied for the visualization of the cylindrical water flow behind the shock wave generated by high-power 6 GW nanosecond time-scale underwater electrical discharge. The flow was visualized during the first microsecond of the wire explosion process in the region between the expanding exploding wire discharge channel and the shock wave. The optical methods, combined with the hydrodynamic calculation, enable an accurate estimation of the energy transferred from the discharge to the water flow. The estimated efficiency of the transformation of the electrical dissipated energy to the mechanical energy of the generated compressed water flow is ∼15%.

Continuous wave operation of a non-self-sustained electric discharge pumped oxygen-iodine laser

Abstract: This letter discusses operation of an electric discharge excited oxygen-iodine laser using a high-pressure, non-self-sustained pulser-sustainer discharge. Small signal gain on the 1315 nm iodine atom transition and the laser output power are measured in the M = 3 supersonic cavity downstream of the discharge section. In a 15% O 2 – 85 % He mixture, at a discharge pressure of 60 torr and discharge power of 1.5 kW , the highest gain measured in the M = 3 cavity is 0.022 % ∕ cm , at the flow temperature of T = 100 ± 10 K . At these conditions, the laser output power is 0.28 W .

Comparison of atmospheric-pressure helium and argon plasmas generated by capacitively coupled radio-frequency discharge

Abstract: In this paper, the electrical discharge characteristics of plasmas generated in coaxial cylindrical electrodes capacitively powered by a radio-frequency power supply at atmospheric pressure are investigated with respect to helium and argon gases. The electrical discharge parameters, voltage (V), current (I), and power (P), are measured for both helium and argon plasmas, and the electron temperatures and electron densities for them are evaluated by means of the equivalent circuit model and the power balance equation. By comparison of the discharge characteristics of the helium and argon plasmas, it is found that the discrepant macroscopic characteristics of helium and argon plasma, viz., current and voltage characteristics and current and power characteristics, are owed to their own intrinsic microscopic parameters of the helium and argon atoms, such as the first excited energy, the ionization energy, the total cross section, and the atom mass. Furthermore, the influences of the additive gas, oxygen gas, on the electrical discharge characteristics are also investigated in the helium and argon plasmas, which are closely related to the electron temperature of plasmas.

Study on Expansion Process of EDM Arc Plasma

Abstract: In order to understand the phenomena of electrical discharge machining (EDM), the characteristics of transition arc plasma in EDM were investigated. The arc plasma was directly observed with a high speed video camera. In addition, to learn more about arc plasma expansion, plasma temperature was measured by spectroscopy. The arc plasma temperature was obtained by measuring the radiant fluxes of two different wavelengths from the arc plasma and applying the line pair method. Furthermore, a new expansion model for EDM arc plasma was proposed based on the observations, and validated by comparing experimental and computed results of the discharge crater.

The Effects of Reaction Conditions on Liquid‐Phase Hydroxyl Radical Production in Gas‐Liquid Pulsed‐Electrical‐Discharge Reactors

Abstract: High-voltage gas-, liquid- and gas-liquid-phase pulsed electrical discharges are an emerging technique in environmental pollutant degradation, which that are char terized by the production of hydroxyl radicals as the primary degradation species. The initiation and propagation of the electrical discharges depends on several physical, chemical and electrical parameters. These parameters also influence the physical asd chemical characteristics of the discharges, including the production of reactive species such as OH*, and H 2 O 2 . This paper focuses on quantification of hydroxyl radicals using chemical probes (DMSO and NaTA) in three different reactor configurations: reference (purely liquid-phase discharge), hybrid-series (combined gas-liquid discharge), and hybrid-parallel (combined gas-liquid discharge) for a wide range of operating conditions. The operating conditions that are evaluated are: input power, initial condufttwty of solution, temperature of solution, presence of radical scawagers and additives in sehttica.

Generation of Active Oxidant Species by Pulsed Dielectric Barrier Discharge in Water-Air Mixtures

Abstract: Experimental research into the electrical and optical parameters of pulsed dielectric barrier discharge (PDBD) was undertaken. PDBD was applied to humid air containing water droplets as a means of water oxidative treatment with short-living species generated in the discharge zone. In spectral analysis of PDBD, only small concentrations of nitric oxides were detected at the resulting electric field strength and electron mean energy sufficient for generation of OH-radicals. The water droplets served as electric field strength concentrators: PDBD was ignited close to the water droplets' surface.

Atmospheric pressure glow discharge plasma and its applications in textile

Abstract: Plasma, a partially-ionized gas generated by an electrical discharge or h igh temperature, i s of d ifferent types and can be classified based on pressure, temperature, source of energy and type of gases. Cold plasma is generated by electric d ischarge at near-ambient temperatures and can be used for surface modification of text i le substrates. This paper reports a brief review of the various plasma and their applications for text i le modifications. For textile modifications, atmospheric pressure glow discharge cold plasma is more suitable because it can be designed for continuous treatment of texti le. However. the main challenge in atmospheric plasma i s to obtain a stable glow ( fi lament-free) discharge over a large surface area suitable for the safe treatment of textile. At l IT-Delhi . uniform glow discharge plasma at the atmospheric pressure over large surface area has been developed by opt imizing reactor design and process parameters. Using this plasma. polyester (PET) and nylon fabrics were treated for 1 0-60 s under different gasses. The treatment significantly enhanced the water absorbency and surface energy of both the nylon and PET fabrics. In nylon-6, the properties imparted by plasma treatment did not change even after 25 days. However. in PET, the absorbency and surface energy were found to reduce slowly with t ime of storage. The samples did not degrade during plasma treatment and showed insignificant change in mechanical properties. The atmospheric pressure glow di scharge plasma can effectively and safely be used to modify surfaces of texti le substrates at reduced process and env i ronment cost.

System, method, and apparatus for an intense ultraviolet radiation source

Abstract: An intense ultraviolet radiation source is disclosed that may be operated in substantially any arbitrary gas environment, without regard to a containment envelope for the ultraviolet radiation source. The intense ultraviolet radiation source can be generated by applying a pulsed or continuous electrical discharge to a partially ionized combustion flame via two electrodes. The combustion flame and electrical discharge can be focused, contained, or confined by gas pressure, electric fields, and/or magnetic fields. Optionally, the thermal energy in the flame and the electrical discharge power input may be augmented with an electromagnetic radiation source, such as a radio-frequency induction heater, a laser, or a microwave generator. Impurities may be placed in contact with or added to the fuel and/or the oxidizer to further alter the emitted ultraviolet radiation spectral brightness as needed. The ultraviolet source may be applied to the molecular dissociation of pollutants in exhaust gas streams of combustion systems. The efficient dissociation of such pollutants requires UV in the wavelength ranges of the vacuum ultraviolet band (100 nm-180 nm) and the UV-C band (180 nm-280 nm).

Comparison of different methods of measurement of pressure of underwater shock waves generated by electrical discharge

Abstract: Different methods for measurement of strong underwater shock waves pressure pulses with peak pressures of up to 200 MPa and rise time of tens to hundreds of nanoseconds are described and compared. The experimental techniques include direct methods of pressure measurement using various electromechanical gauges such as quartz, carbon-based, and commercially available PCB gauges, and nondirect methods based on measurement of the velocity of the shock wave such as time-of-flight and fast-streak photography. Advantages and disadvantages of the used gauges and methods are discussed. The shock waves were produced by underwater electrical discharge (discharge current amplitude ≤100 kA, pulse duration ≤5 μs) initiated by an exploding wire. A good correspondence between the pressure amplitudes measured by the various gauges and methods was observed. The obtained dependence of the shock wave pressure on the distance from the discharge channel was found to be best fitted by a r −0.7 law. It is also shown that none of these methods can be used to determine the time evolution of the pressure behind the front of the shock wave.

Effects of Platinum Electrode on Hydrogen, Oxygen, and Hydrogen Peroxide Formation in Aqueous Phase Pulsed Corona Electrical Discharge

Abstract: Platinum, when used as the high-voltage needle electrode in pulsed corona electrical discharge in water, reduces the production rates of molecular hydrogen, hydrogen peroxide, and molecular oxygen by the discharge, in comparison to the production rates of those species when a nickel−chromium electrode is used. Reactions between hydrogen and oxygen and hydrogen and hydrogen peroxide are proposed to explain this result. It is proposed that these reactions occur on the surfaces of particles sputtered from the discharge electrode.

Pulsed dielectric surface flashover in nitrogen at atmospheric conditions

Abstract: Dielectric flashover along insulators in vacuum has been comprehensively researched in the past. Less studied, but of similar importance, is surface flashover at atmospheric pressures and the impact of an atypical electrode geometry, humidity, and ultraviolet (UV) illumination. Previous research has shown distinct discharge behavior in air and nitrogen environments for an electrode geometry in which the applied electric field lines curve above the dielectric surface. It was concluded that the discharge development path, whether along the electric field lines or the surface of the dielectric, is related to the oxygen content in the atmospheric background. It is believed that this dependence is due to the discharge's production of UV radiation in an oxygen rich environment. Thus, experiments were conducted in a nitrogen environment employing UV surface illumination in order to observe the affects on the flashover spark behavior. From the experimental data, it can be ascertained that UV illumination and intensity play a significant role in the discharge development path. Based on these results an explanation of the physical mechanisms primarily involved in unipolar surface flashover will be presented. Additional experiments regarding the effects of humidity on the discharge behavior will be discussed as well

The Electrical Insulation Characteristics for a HTS Cable Termination

Abstract: A research on several characteristics such as volume breakdown and surface discharge of insulators for a termination of power transmission class high temperature superconducting (HTS) cable was performed. In this paper, we investigated the surface discharge of glass fiber reinforced plastic (GFRP) in the air, nitrogen gas (GN2) and cryogenic nitrogen gas (CGN2) media. The breakdown characteristics of these media were also studied. Experimental results revealed that flashover voltage greatly depends on pressure, temperature, the kinds of insulating media and voltages. However, it is shallowly affected by shape and material of electrode. The breakdown voltage of liquid nitrogen (LN2), GN2 and CGN2 deeply depends on the shape and dimension of electrode, kinds of voltages and pressure. Moreover, the breakdown voltage of CGN 2 and flashover voltage of GFRP in the CGN2 is also influenced by temperature and vapor-mist density of the gas

Numerical study on the dynamics of an electrical discharge generated bubble in EDM

Abstract: In this paper, the influence of hydrodynamic behaviour of dielectric liquid media around a rapidly growing small spherical bubble in the process of electrical discharge machining (EDM) between the tool and the workpiece on material removal from the workpiece is investigated. The tool and the workpiece are assumed as two parallel rigid boundaries with dielectric liquid between them. The boundary integral equation method is applied for numerical solution of the problem. Results illustrate the time dependent shapes of the bubble generated between the two parallel rigid boundaries due to the electrical discharge. Results also indicate that continuous growth of the gas bubble leads to a sharp drop of pressure within the bubble which results in the sharp pressure drop over the surfaces of the tool and the workpiece. This pressure drop over the surfaces of the tool and the workpiece causes expelling of the gas dissolved in the molten metal and helps the molten material to escape.

Continuous-wave laser oscillation in subsonic flow on the 1315nm atomic iodine transition pumped by electric discharge produced O2(aΔ1)

Abstract: Herein the authors report on the demonstration of a continuous-wave laser in subsonic flow on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited electric discharge. The electric discharge was sustained in an O2–He–NO gas mixture. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow to shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 540mW in a stable cavity with two 99.993% reflective mirrors.

Laboratory investigation of positive streamer discharges from simulated ice hydrometeors

Abstract: Positive streamer discharges have been observed from ice crystals grown from the vapour under controlled temperature and air pressure corresponding to the standard atmosphere and also constant air pressure of 850 hPa. Crystals of size comparable to larger precipitation crystals were grown in a vapour diffusion chamber at various temperatures and pressures, and were subject to electric fields using an in situ electrode assembly. Results show that individual positive streamer discharges can occur at temperatures from near freezing down to at least −38°C when subject to electric fields on the order of 500kV m−1, in contrast to previous reports of continuous positive streamer discharges occurring only at temperatures warmer than −18°C for pure ice crystals. These results suggest that positive streamer discharges can occur on frozen precipitation particles at high altitudes in thunderclouds, given a sufficiently strong electric field. Such discharges may be a necessary element of the lightning-initiation process. Copyright © 2006 Royal Meteorological Society

Measurement of sparkover voltage and time lag characteristics in CF3I–N2 and CF3I– air gas mixtures by using steep-front square voltage

Abstract: A square pulse voltage is useful for studying electrical discharge physics or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V– t) characteristics of CF3I gas, which has very low environmental effects and high dielectric strength, and its mixtures with nitrogen gas or air in a very short time range below a microsecond. They are measured by using a steep-front square voltage with a rise time of 16 ns and a peak value of 200 kV. Pure CF3I gas has 20% higher dielectric strength than SF6 gas. The V– t characteristics of CF3I–N2 or CF3I– air gas mixtures, which contain 60% CF3I gas, are equivalent to those of pure SF6 gas at the same total pressure. A quantitative evaluation of V– t characteristics by the equal-area criterion is also performed. The equal-area parameter which is obtained by applying a voltage high enough to make the formative time lag dominant should be chosen. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 1–7, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20325

On the Performance of Ozone Generators Working with Dielectric Barrier Discharges

Abstract: The parameters, which determine the performance of ozone generators, are efficiency and maximum ozone concentration. The efficiency from oxygen has been found to be nearly independent on the kind of barrier discharge arrangement (volume, surface, coplanar), while the ozone concentration saturation level depends on the specific design of the generator. These phenomena are explained with features of the discharge process and the properties of chemical reactions, respectively. The importance of a limit in the energy density of the discharge is highlighted.

Diagnostics of PDP micro-discharges

Abstract: Plasma display panel emission measurements are correlated with panel efficacy trends, and directions for the improvement of the discharge efficiency are derived. An increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared indicates an increased Xe excitation efficiency. Also, the time dependence and the spatial distribution of the Xe emission are important discharge characteristics. Experiments reveal that a high panel efficacy is obtained, especially for design and driving conditions that govern a fast and spatially distributed discharge development. A high sustain voltage V>200 V causes a "high efficiency discharge mode." It is proposed that in this mode, the cathode sheath is not, or is incompletely, formed during the rise of the discharge current. Then the electric field in the discharge cell is dominated not by the space charges, but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe-excitation. Under the fast discharge buildup conditions also the electron-heating efficiency increases due to a decrease of the ion heating losses in the cathode sheath. A high sustain voltage combines well with a high Xe content gas mixture, that further increases the discharge efficiency. Changes in the phosphor to Xe- and Ne-emission ratio show that for higher Xe content, a lower electron temperature accounts for a more efficient Xe excitation. Further, the use of a TiO/sub 2/-layer underneath the phosphor causes an increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared, i.e., an increased Xe excitation efficiency. As a result, a high efficacy of 5 lm/W and a high luminance of 5000 cd/m/sup 2/ have been realized in a 4-in color plasma display test panel design with a 50% Xe in Ne gas mixture, a TiO/sub 2/-layer underneath the phosphor, and a high sustain voltage 260-290 V.

Measurement of the electric field radiated by electrostatic discharges

Abstract: The aim of this work is the investigation of the transient electric field radiated by two different commercial generators of electrostatic discharges for various charging voltages. Measurements of the electric field generated by contact electrostatic discharges have been conducted a few centimetres away from the discharge point. In this paper the current transducer, which is used for the measurement of the discharge current, is mounted on a grounded metal plane. It is the first time that measurements of the electric field have been conducted along three different directions in relation to the electrostatic discharge generator. Measurements prove that each generator produces a different transient electric field, which affects the equipment that is tested in a different way. Also, each generator produces a different electric field depending on the orientation of the generator. Finally, comparisons of the electric field for both generators and useful conclusions for the decrease of the electric field are presented.

Mixing effects in postdischarge modeling of electric discharge oxygen-iodine laser experiments

Abstract: In an electric discharge oxygen-iodine laser, laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is obtained by a near resonant energy transfer from O2(aΔ1) which is produced using a low-pressure electric discharge. The discharge production of atomic oxygen, ozone, and other excited species adds higher levels of complexity to the postdischarge kinetics which are not encountered in a classic purely chemical O2(aΔ1) generation system. Mixing effects are also present. In this paper we present postdischarge modeling results obtained using a modified version of the BLAZE-II gas laser code. A 28 species, 105 reaction chemical kinetic reaction set for the postdischarge kinetics is presented. Calculations were performed to ascertain the impact of a two stream mixing mechanism on the numerical model and to study gain as a function of reactant mass flow rates. The calculations were compared with experimental data. Agreement with experimental data was improved with the addition of new kineti...

Numerical modeling of ozone production in direct current corona discharge

Abstract: Ozone has many industrial uses, including treatment of municipal water, wastewater, cooling towers, industrial process water, effluent water treatment, food processing, through to water fit for consumption and marine life. In this paper, we study the ozone production by negative electric corona discharge, witch involves passing the feed of gas, air rich, through an electrical discharge. This is done by applying a high voltage between two electrodes separated. The electrical charge between two surfaces creates a sequence of dissociation and subsequent collisions of oxygen with electrons creating ozone. So to describe this phenomenon we use (1D) numerical model for the charged particles. The electron number density and electric field are determined from solution of the one-dimensional coupled continuity equations of charge carriers and Poisson’s equation. Simulation result show the variation of the electrical field, charged particles density, and ozone (O3) particle density. 2006 Elsevier B.V. All rights reserved.

Control of combustion by generation of singlet oxygen molecules in electrical discharge

Abstract: The possibility of the combustion enhancement in a supersonic flow of H2-O2 mixture by activation of molecular oxygen in electrical discharge is analyzed. It is demonstrated that abundance of excited oxygen molecules O2(a 1Δg) and O2(b 1‑ g + ) in the oxygen plasma is responsible for accelerating chain-branching reactions and allows one to arrange the stable combustion in a low temperature supersonic flow at a small discharge energy deposited to the gas.

High-Speed Inlet Customization by Surface Electrical Discharge

Abstract: Experimental and analytical study of near-surface transversal quasi-DC discharge effect on high-speed flow structure has been carried out for a model of supersonic inlet. Two main topics are discussed: the different discharge modes characteristics and the discharge influence on extrusive layer configuration downstream of the power deposition zone. The discharge properties control by external magnetic field has been demonstrated experimentally. Vibrationally non-equilibrium plasma effect on shock structure has been demonstrated by experimental data comparison for air (long relaxation time), carbon dioxide (short relaxation time), and argon (no vibrational excitation).