Pulsed Electric Discharge Research Articles

Chemical and Physical Characteristics of Pulsed Electrical Discharge Within Gas Bubbles in Aqueous Solutions

The chemical and physical characteristics of pulsed electrical discharge within gas bubbles immersed in an aqueous solution were investigated using a reactor with long protrusion length high voltage needle electrodes. Argon gas was introduced at the base of the needle electrode causing gas bubbles to flow upwards in contact with the needle. The effects of needle protrusion length were evaluated by using 2, 4, and 6 cm length needles under a wide range of power input (3–78 W). No significant differences in chemical or electrical characteristics were found among the different protrusion lengths. H2 and H2O2 generation rates were proportional to input power and the energy yield efficiency for these species was not affected dramatically by input power. The results of discharge within bubbles in aqueous solution were also compared with those for direct liquid phase discharge and gas phase discharge above the liquid surface.

A kinetic model of a PD pulse within voids of sub-millimeter dimensions

A two-dimensional Particle-in-Cell based Monte Carlo Collision model is used to study the dynamics of a spark-type electric discharge pulse within narrow dielectric cavities of submillimeter dimensions. The gas within the cavity is taken to be air at atmospheric pressure. The development of an avalanche through primary and secondary ionization processes, is followed till extinction. Secondary processes including photo-emission and ion-emission from the cathode are considered. The model is seen to successfully simulate the evolution of the discharge and yield useful information about the build-up of space charge within the gaseous channel, consequent modification of the electric field, ionic and electronic currents, and charge accumulation on the electrodes at end of discharge pulse. A significant contribution of this work is that the simulated discharge within the cavity is coupled through the electrodes, with an external circuit comprising of a voltage source. The effect of different electrode configurations viz. metallic-metallic, dielectric-metallic and dielectricdielectric, as might occur at pd initiation sites, is studied. This is seen to significantly affect many of the parameters studied, especially the charge deposition at discharge extinction. The magnitude of the discharge pulse and its rise-time are also seen to be affected. The phase-space scatter plots for electrons, positive and negative ions are obtained, which help to understand the manner in which the discharge progresses over time.

Effects of Electrode Protrusion Length, Pre‐Existing Bubbles, Solution Conductivity and Temperature, on Liquid Phase Pulsed Electrical Discharge

AbstractThe effects of high voltage electrode needle protrusion length and the presence of low density pre‐existing bubbles on liquid phase pulsed electrical discharge were investigated. Liquid phase pulsed corona discharge was operated with two different protrusion length needle electrodes (short – 2 mm and long – 20 mm) with different bulk solution conductivities (5 µS · cm−1 and 150 µS · cm−1) at room temperature (25 °C) and near boiling (95 °C). Chemical reactions formed in the discharge were also investigated by measuring the generation rates of hydrogen (H2), oxygen (O2) and hydrogen peroxide (H2O2).magnified image

General Nature of Luminous Body Transition Produced by Pulsed Discharge on an Electrolyte Solution in the Atmosphere

AbstractA luminous body (LB) was produced by a pulsed electric discharge that initiated at the tip of the cathode and widely propagated on the surface of an electrolyte in the atmosphere. Entire images of the LB transition taken by a high‐speed camera are visually demonstrated for the first time. It is indicated that the entire phenomenon of the LB transition can be classified into three sequential processes, regardless of the experimental conditions. It is estimated that the bright and octopus‐like discharge, which may act as a source of high‐energy ions and atoms, plays an essential role to make the mechanism of LB phenomena clear. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivities. I. Expansion mechanism

Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10−6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton) at atmospheric pressure at a distance of ∼1.2–2.5 cm from the discharge boundary. It was shown that the structure of such discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity.

Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivities. II. Energy balance and equation

Based on the mechanism of pulsed electric discharge expansion in dense gas (at atmospheric pressure and above), an equation for the discharge channel radius was derived from the discharge energy balance, taking into account expenditures for ionization of gas involved in the discharge, Joule heating of plasma, and the discharge work against the ambient gas pressure. For the initial stage of the development of such discharge, a solution to this equation was obtained, which is in agreement with experimental data within the measurement error.

Some considerations on concerning the electrical discharge threading

The electrical discharge machining (EDM) is a machining process based on pulsed electrical discharge effects, which appear between the electrode tool and the workpiece. One may say that the electrical discharge machining is one of the most frequently used nonconventional processes, allowing the obtaining of surfaces which cannot be otherwise achieved through classical machining methods. The electrical discharge machining is also used in order to manufacture hard and extra-hard materials; this process is used to obtain pieces with complex shapes, which would otherwise be difficult or even impossible to obtain, by the use of classical machining methods. The profiled surfaces can be classified according to the final service role. In this respect one may mention threaded, spherical, conical or polygonal surfaces as profiled surfaces. The threaded surfaces could be obtained by classical methods and nonconventional machining methods, among which cutting machining and plastic deformation as classical machining methods are worth mentioning.

Pulsed electrical discharges in water for removal of organic pollutants: a comparative study

In this study, the efficiency of different types of pulsed electrical discharges for the removal of organic pollutants from wastewater has been determined. Three discharge types, either in the water volume or in close proximity to the water surface are studied. The production of hydrogen peroxide in pure water, and the degradation of two typical pollutants (4-chlorophenol and 4-nitrophenol) is measured together with the amount of electrical energy dissipated in discharges. It is shown that the energy yield for the degradation of organic pollutants, expressed in terms of degraded moles per Joule, strongly depends on the discharge type. The highest efficiency is obtained with pulsed corona discharges in humid air above the water surface. A lower efficiency is found with spark discharges in water, and the less efficient process is constituted by streamer discharges in water. The influence of ferrous ions added to solutions is also very different according to the discharge type. This helps to get a better understanding of the degradation processes involved with the different discharge types.

Decomposition of Energetic Materials by Pulsed Electrical Discharges in Gas-Bubbled Aqueous Solutions

The application of high-voltage pulsed electrical discharges in bubbled water (PDBWs) for the remediation of solutions containing energetic compounds such as RDX, HMX, and TNT was investigated. Using low-energy pulses ( ~ 300 mJ/pulse), it was found that the PDBW was highly selective toward the type of energetic compound. The effects of a catalyst and of the pH value of the solution on the degradation of energetic compounds were also studied. HMX decomposition is most effective when the PDBW is used at low pH under Fenton reaction conditions. The degradation efficiency was higher for oxygen (O2) than for argon (Ar) as the bubbled gas.

Pure rotational spectra of the CCCF radical

Pure rotational transitions of a new carbon-chain radical CCCF in a supersonic jet have been observed for the first time using a Fourier-transform microwave spectrometer with a pulsed-discharge nozzle. The radical was produced by a pulsed electric discharge in a C(2)H(2) and CF(4) mixture diluted to 0.1% and 0.1% with Ne, respectively. Rotational transitions with spin and hyperfine splittings have been observed in the region from 9.1 GHz for N(K(a)K(c)) = 1(01)-0(00) to 27.3 GHz for N(K(a)K(c)) = 3(03)-2(02). The rotational constant, the spin-rotation interaction constant, and the hyperfine coupling constants due to the F nucleus have been precisely determined from the least-squares analysis, yielding B = 4555.8043(44), gamma(eff) = -7.105(16), b(F,eff) = 368(19), and c(eff) = -284.832(61) MHz. The determined molecular constants were compared with those obtained from high-level ab initio calculations and concluded that the CCCF radical has a bent ground state X(2)A(').

Influence of pH on inactivation of aquatic microorganism with a gas–liquid pulsed electrical discharge

Inactivation of Escherichia coli in water was experimentally studied, with pulsed electrical discharges in a hybrid gas–liquid reactor. The pH was dramatically decreased from 7 to ∼3 within 60 min, accompanying with a 6-log reduction. To evaluate the contribution of pH on inactivation, a set of experiments were designed and tested. Results indicate that the contribution of low pH to the inactivation could be neglected compared to that of electrical discharges. On the other hand, the decrease of pH could be eased as carbonate or phosphate buffer was added to the treated water. However, the inactivation efficiency was greatly reduced because the buffers could deplete the active species formed in electrical discharges. Besides, a new finding is addressed in this paper that the water after plasma treatment still owns a certain extent of inactivation ability, functioning like the free chlorine residual. The environmental adaptation ability of E. coli to electrical discharges was also investigated.

Fourier-transform microwave spectroscopy of the CCCCl radical

Pure rotational spectra of the CCCCl radical in a supersonic jet have been observed for the first time by Fourier-transform microwave spectroscopy. The radical was produced by a pulsed electric discharge in a C(2)H(2) and CCl(4) mixture diluted to 0.3% and 0.2% with Ne, respectively. Transitions with spin and hyperfine splittings were observed for two isotopologs, CCC(35)Cl and CCC(37)Cl, in the region from 11.4 GHz for N=2-1 to 34.2 GHz for N=6-5. The molecular constants including the hyperfine coupling constants due to the Cl nucleus have been determined precisely. From the rotational analyses and high-level ab initio calculations, the molecular structure of the CCCCl radical is concluded to be bent in the ground electronic state.

Electrically Assisted Extraction of Soluble Matter from Chardonnay Grape Skins for Polyphenol Recovery

The objective of this study was to investigate the effects of pulsed electric field (PEF) and high-voltage electrical discharges (HVED) application on the efficiency of aqueous extraction of total soluble matter and polyphenols from grape skins ( Vitis vinifera L.) at different temperatures within 20-60 degrees C. The highest level of polyphenol concentration C was reached after about 60 min of extraction for HVED treatment: C(HVED) = 21.4 +/- 0.8 micromol of gallic acid equivalent (GAE)/g of dry matter (DM). Almost the same level of C was reached after 180 min of extraction for the PEF-treated skins. These levels exceeded the value C = 19.1 +/- 0.5 micromol of GAE/g of DM for the untreated samples. The difference between degrees Brix values for HVED-treated and untreated systems decreased with temperature increase (from 40 to 60 degrees C), but a large difference in the total amount of polyphenols was observed for HVED-treated and untreated systems. The activation energies were W(u) = 31.3 +/- 3.7 kJ/mol and W(PEF) = 28.9 +/- 5.5 kJ/mol for untreated and PEF-treated systems, respectively.

Mechanism of pulse discharge production of iodine atoms from CF3I molecules for a chemical oxygen–iodine laser

The pulsed chemical oxygen–iodine laser (COIL) development is aimed at many new applications. Pulsed electric discharge is most effective in turning COIL operation into the pulse mode by instant production of iodine atoms. A numerical model is developed for simulations of the pulsed COIL initiated by an electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is re-calculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions, second-kind collisions and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. It is concluded that there is satisfactory agreement between theory and the experiment. The prevailing mechanism of iodine atom formation from the CF3I donor in a very complex kinetic system of the COIL medium under pulse discharge conditions, based on their detailed numerical modelling and by comparing these results both with experimental results of other authors and their own experiments, is established. The dominant iodine atom production mechanism for conditions under study is the electron-impact dissociation of CF3I molecules. It was proved that in the conditions of the experiment the secondary chemical reactions with O atoms play an insignificant role.

Stages of an electric discharge gliding on a water surface

Three stages of a pulse electric discharge were revealed. The discharge occurred in the atmosphere along a free water surface between a tip placed at some distance from the water surface and a distant electrode immersed in the water.

Application of pulsed electrical discharge lamps for bactericidal treatment

A bactericidal treatment analytical analysis of the potentialities of pulsed UV lamps has been carried out. A comparison of traditional low- and high-pressure mercury lamps has been performed. Devices with pulsed xenon lamps are characterized by higher power consumption, lower resources, and higher exploitation expenditures than low-pressure mercury lamps. Xenon lamps may be used in equipment or under conditions in which the mercury presence is barred.

On mechanisms of interaction in electrosurgery

Electrosurgery is broadly used in a wide variety of surgical procedures, yet its underlying mechanisms of interaction are poorly characterized. Fundamentals of electrosurgery have not changed much since the 1930s—cutting is still performed using continuous RF waveforms, leaving a collateral damage zone of hundreds of micrometers in depth. Pulsed waveforms with variable duty cycle are used mostly for tissue coagulation. Recently, we have demonstrated that electrosurgery with microsecond bursts applied via microelectrodes can provide cellular precision in soft tissue dissection. This paper examines dynamics of pulsed electrical discharges in conductive medium, and accompanying phenomena, such as vaporization, cavitation and ionization. It is demonstrated that ionization of the vapor cavity around the electrode is essential for energy delivery beyond the vaporization threshold. It is also shown that the ionization threshold voltage and resistance of the plasma-mediated discharge are much lower in the negative phase of the discharge than in the positive one. Capacitive coupling of the ac waveform to the electrode compensates for this asymmetry by shifting the medium voltage on the electrode, thus increasing the positive and decreasing the negative amplitudes to achieve charge balance in the opposite phases. With planar insulated electrodes having exposed edges of 12.5 μm in width and bursts of 40 μs in duration even tough biological tissues can be dissected with cellular precision. For example, cartilage dissection is achieved with pulse energy of 2.2 mJ per millimeter of length of the blade, and leaves a thermal damage zone of only 5–20 μm in width.

Electrically-assisted extraction of bio-products using high pressure disruption of yeast cells ( Saccharomyces cerevisiae)

The efficiency of combined electrically-assisted high pressure homogenization techniques for disruption of wine yeast cells ( Saccharomyces cerevisiae bayanus, strain DV10) in an aqueous suspension (1% w/w) was studied. The pulsed electric field (PEF) and high voltage electric discharge (HVED) were applied at electric field strengths of 10 kV/cm and 40 kV/cm, respectively. The high-pressure homogenization (HPH) technique was applied within pressure range 30–200 MPa at different number of passes (1–20). Releasing of intracellular ionic content was characterized by conductivity disintegration index Z (0–1), releasing of high molecular weight content was analyzed using spectroscopy and electrophoresis methods. It was shown that releasing efficiency of ionic components, enzymes, proteins and other bio-products dramatically depended on the applied method of disruption. Extraction efficiency was rather high for ionic components and small for high molecular weight components in PEF or HVED pre-treated suspensions. However, application of the combined HVED-HPH technique resulted in material loss of integrity by yeast cell walls. Even small disintegration ( Z i = 0.15 ± 0.05) initially induced by HVED pre-treatment resulted in noticeable acceleration of HPH disruption kinetics. The proposed combined HVED-HPH technique may have a good potential in future biotechnological and food applications.

Electronic spectroscopy of the jet-cooled arsenic dicarbide (C2As) free radical

The (2)Delta(r)-X (2)Pi(r) band system of the jet-cooled arsenic dicarbide (C(2)As) free radical has been recorded by laser-induced fluorescence (LIF) techniques in the 685-588 nm region. The radical was produced in a pulsed electric discharge jet using a precursor mixture of AsCl(3) vapor and methane in high pressure argon. A series of weak bands involving all three excited state vibrations was observed for both (12)C(2)As and (13)C(2)As. High-resolution spectra of the (2)Pi(12) component of the 0(0)(0) bands of both isotopomers were rotationally analyzed, leading to the conclusion that the upper state is (2)Delta with a small spin-orbit splitting (A = 2.78 cm(-1)). Ground and excited state molecular structures of r(0)(")(CC,ab initio) = 1.2933 A, r(0)(")(CAs) = 1.734(4) A and r(0)(')(CC,ab initio) = 1.2276 A, r(0)(')(CAs) = 1.830(3) A were derived from the B values and our density functional predictions of the C-C bond lengths. Single vibronic level emission spectra were recorded for many of the LIF bands and these were used to obtain the ground state vibrational frequencies and spin-orbit splittings. These data were satisfactorily fitted to a Renner-Teller model which gave (12)C(2)As parameters of epsilon = 0.695(8), omega(1) = 1704.8(20) cm(-1), omega(2) = 161.6(8) cm(-1), omega(3) = 663.6(12) cm(-1), and a spin-orbit constant A = 857.7(11) cm(-1).

The formation of ozone and UV radiation from high-power pulsed electric discharges

High-power electric discharges with pulse energies of from 0.15 J to 4 kJ were studied. The yields of UV photons and ozone were found to be approximately equal, which led us to conclude that discharge con- ditions under which UV radiation and ozone fully destroyed each other were possible. If ozone formation was suppressed, as when a negative volume charge was created in the spark gap region, the flux of UV photons