Corona Discharge In Gas Research Articles

Mass and Mobility of Ions Produced by Radioactive Sources and Corona Discharges.

Positive and negative ions produced by radioactive sources and corona discharges in gases find a number of applications, including charging aerosol particles prior to their measurement by electrical and/or electrical mobility techniques. The degree to which these ions can charge aerosol particles depends on their mobility and mass; properties that are strongly affected by the composition of the carrier gas and the impurities that it contains. We show that when the purity of the carrier gas is increased, the mobility of both positive and negative ions increases by more than 50%, whereas the respective masses reduce by more than 50%. In most cases, the dominant positive species is N4+, whereas NO2- and NO3- prevail for the negative polarity. Differences in ion mobility and mass resulting from the two ionization methods (i.e., radioactive source and corona discharges) remain limited. When volatile methyl siloxanes (VMS) are introduced deliberately to the gas, the mobility of the cations decreases by 39% and their mass increases by 385%, while the dominant mobility and mass peaks of the negative ions remains almost unaffected. Interestingly, introduction of VMS also leads to consistent and reproducible positive ion properties across all variations of the experiments, which can be especially relevant for charging aerosol particles in a reproducible manner. Taken together, the new measurements we report in this paper corroborate prior knowledge that the composition and purity of the carrier gas strongly influence the properties of positive and negative ions generated in aerosol neutralizers, and provide new evidence regarding their evolution in the presence of impurities.

New insight on filamentary charge‐loaded flows originated by pulsating glow‐type unipolar coronas in atmospheric air

AbstractThe diffusional process involving elastic collisions between charge carriers and neutrals has long been the predominant candidate for post‐injection momentum loss in the far wider drift region outside confined DC corona discharges in gases. A supplementary research paradigm is here put forward for the interest of a greater understanding of corona‐assisted unipolar ion flows in atmospheric air. In this respect, the auto‐pulsing mode of glow‐type coronas in air is modelled as a source of momentum whose conservation is substantially preserved across the external transfer region. The tangible prospect of charge‐bearing flows in the form of a filamentary convection, with negligible drifting component, in buffer gas is put forward in relation to spontaneous symmetry‐breaking instability. This setting bears some resemblance to the self‐organised collective behaviour of self‐propelled (active) particles. The value of this scheme gains strength precisely in relation to the strong inhomogeneity of the electric field surrounding electrodes prone to go into corona. On such a basis, it is believed that the drift of corona‐generated ions deserves to be reconsidered in view of the arguments set out in the present modelling.

Partial generalizations of the current-voltage characteristics of corona discharge in gases

Generalizations from the experimental current-voltage characteristics of corona discharge for helium and synthetic air at the positive and negative polarities of a star-shaped discharge electrode at different gas pressures are presented. Similar generalizations are performed for current-voltage characteristics obtained for dried air and a coaxial system of electrodes at various temperatures and atmospheric pressure. The generalization consists in reducing the family of the current-voltage characteristics to a single generalized equation that geometrically represents a segment bisector. Some aspects of the application of similarity methods for corona discharge are considered. Townsend’s structure of the characteristics is confirmed, and this fact can serve as a basis for its wide application.

Сто років формулі Піка для визначення початкової напруженості коронного розряду

This article is dedicated to the memory of well-known electrical engineer Frank William Peek, Junior, who estimated the corona inception electric field on the surface of electrodes with a small radius of curvature which allows for corona discharge inception and also known as the “Peek’s law”. Analyzing Peek’s first publications dated 1911–1915, we have seen that he has elaborated and summarized the laws, which describe the phenomenon of corona discharge in gas on the wires of power transmission line. In particular, Peek presented the final version of the half-empirical formula in 1915, which allows estimating the voltage under which a corona appears on high-voltage wires, as well as estimating the power loss caused by this phenomenon. Attention has been drawn to the unrenowned facts related to Peek’s discovery of the formula. It has been discovered that the scientist was using the mean-value method when working on the formula. Also, attention has been drawn to the reasons of difference in indices (coefficients) in Peek’s formula, which can be seen in literature and publications of different authors in our country, as well as other countries. Based on the results of the research of Peek’s successors, it has been shown that all new charts repeat his formula and differ from it only by the value of numeric coefficients and, sometimes, the exponent in the denominator. Three ways of using his formula have been summarized; its direct application in electric power industry has been shown.

Generalization of the Townsend current-voltage characteristics of a corona discharge

The statistical treatment of the current-voltage characteristics of a corona discharge in gases and the generalization of them on the basis of the theory of similarity is considered. The dependence of the corona discharge current on the applied voltage is assumed to be two-parametric of the Townsend type. The parameters of the current-voltage characteristics are found using the least squares method on the basis of experimental data. The calculated current-voltage characteristics are reduced to a dimensionless form and are generalized in the form of the equation of the first quadrant bisector. The criteria and conditions of similarity of corona discharges are found. By the example of a positive corona discharge in helium at different pressures, there is generalized a number of experimental current-voltage characteristics using the proposed method.

Some peculiar features of electric separation

The most characteristic features of the processes of electrical filtration of ideal and low-conducting dielectric fluids are considered. It is noted that, in liquid dielectrics in highly inhomogeneous electric fields, phenomena similar to those at corona discharge in gases with all its consequences are observed. The processes of electrical purification (separation) are interpreted in terms of a corona discharge. In particular, the electric charging of dispersed particles and their transport to the “electrode-collector” are considered. The threshold phenomena at electric separation such as the appearance and disappearance of the separation effect are treated from the standpoint of a corona discharge as well. Two concepts, namely, the screening of an external electric field by the field’s spatial electric charge and the ohmic resistance of the layer of dispersed particles deposited on the collector are discussed. Both approaches lead to identical results. To clarify the above-mentioned theoretical concepts and to work out recommendations for the modernization and efficient use of electrical separation, further studies of the experimental time-current characteristics of the process of the separation are needed.

Development of ac corona discharge modes at atmospheric pressure

Corona discharges in gases exist under several distinctive forms. In this paper, a survey study has been made of ac corona discharge modes generated in some different gases fed in a wire-duct reactor with a constant rate of flowing at atmospheric pressure. The properties of different corona modes are analyzed under some condition transitions from Trichel pulses to a steady glow. In the course of the presented experimental work, numerous apparent contradictions with earlier observations necessitated further study and are given to provide more information on the physical mechanisms of the ac corona discharges. Furthermore, we have gained insight into some new technologies and applications of the environmentally friendly corona and plasma discharges.

Simulation Model of the Decomposition Process of Phenol in Water by Direct Contact of Gas Corona Discharge in a Cylindrical Reactor

An empirical model is proposed for the decomposition process of phenol in water by direct contact of gas corona discharge in a cylindrical wetted-wall reactor. The proposed model is based on an assumption that reactive radicals in water, OH, induced by the corona discharge are the main species to decompose phenol and its derivatives. The phenol degradation characteristics calculated by this model are successfully correlated with the experimental data obtained with many varied parameters, such as the discharge current, diameter of the wire cathode, axial length of the discharge zone, radius of the cylindrical anode, and water flow rate. The calculated results can also show the effect of the ion wind. The proposed model will be useful to the design of water purification systems using the relevant method, which has lately been developed as an effective technique to decompose stable organic compounds.

Influence of dissolved inorganic additives on decomposition of phenol and acetic acid in water by direct contact of gas corona discharge

Abstract The influence of dissolved several inorganic contaminants into water was examined on the decomposition of aqueous organic compounds by direct contact of gas corona discharge. It was found that addition of 0.01 mol l −1 NaOH into water significantly improves the decomposition of aqueous phenol while the addition of HCl of the same concentration inhibits the decomposition rate. As it is known that phenol is converted to stable acetic acid during the decomposition process in the reactor, the influence of NaOH, HCl, H 3 PO 4 and NaCl was examined on the degradation of acetic acid. As a result, dissolved Cl − inhibits its decomposition efficiency. It is also found that this decomposition rate is significantly improved by raised pH which is higher than 11.

Promotion of crystal growth rate in aqueous solution by direct contact with gas corona discharge

AbstractA new technique to promote crystal growth in aqueous solution using gas plasma is proposed. In this method, short‐lived radical species produced in solution which is contacted with gas corona discharge play a role to increase chemical potential of inorganic solute. In an experimental examination, single crystal of KDP was grown in a supersaturated solution which receives oxygen ions and radicals from adjacent corona discharge in air. KDP crystal has two unique growth faces (100) and (101), and the growth rates of both faces were increased considerably by generating the corona discharge. The both growth rates with and without corona discharge were well converged by one function based on chemical potential supersaturation. This result revealed that the solution in contact with gas corona discharge has a larger capacity of chemical potential than that without the discharge. Short‐lived species induced by gas corona discharge are considered to be anti‐solvents to cause this effect. The crystal growth process proposed here is considered to be an excellent method in terms of low impurity inclusion because such short‐lived species do not remain in the final crystal products and solution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simulation of corona discharge in point–plane configuration

A numerical technique is proposed for determining the distributions of electric field and charge density in the case of a positive corona discharge in gas in the point–plane geometry. This technique is based on the boundary and finite elements methods for obtaining the harmonic and space charge components of the electric field, respectively, and on the method of characteristics to determine the charge density distribution. The numerical simulation gives the current density distribution on the ground plate, which compares favorably with the ones measured using a cylinder–cone needle with a tip of spherical shape.

Decomposition of Aqueous Phenol by Direct Contact of Gas Corona Discharge with Water: The Influence of Current Density and Applied Voltage

A cylindrical wetted-wall reactor in which high-voltage corona discharge was generated in gaseous space was applied to decompose phenol dissolved in water. It was found that the decomposition efficiency depends on current and current-density. When the current density was decreased by extending the axial corona region length at a constant current, electron efficiency decreased with the increase of corona region length in the range of relatively low discharge current, while this trend was reversed in the range of high discharge current. Experiments with varied applied voltages by the use of varied cathode diameters suggested that these reversed trends can be explained as follows. (1) The effect of increasing voltage at increasing current density, which increases the reactive radicals, becomes significant at the relatively low current condition. (2) At the high current condition, the voltage becomes excessively high so that ion-wind will disturb the uniformity of the discharge due to a waving water surface. Nevertheless, the condition with relatively low voltage by the use of long discharge region length and thin cathode diameter leads to high energetic efficiency in all discharge current ranges examined here.

Decomposition of Phenol in Water by a Cylindrical Wetted-Wall Reactor Using Direct Contact of Gas Corona Discharge

A water purification reactor using direct contact of gas corona discharge with water is developed into a cylindrical-anode wetted-wall reactor. In a modification from the previous plate anode to the present cylindrical anode, it is expected that reactive radicals produced in a plasma region around a wire cathode in a gas phase can efficiently reach the surface of a flowing-water film so that reactive species such as an OH radical can be effectively produced in water. In this study, aqueous phenol was decomposed using the modified reactor to evaluate its efficiency. As a result, the electron efficiency and energetic efficiency of the cylindrical-anode wetted-wall reactor were respectively 2−3 and 3−4 times greater than those of the plate-anode reactors. Furthermore, the activity of the radical-producing plasma in the proposed reactor was 2 orders of magnitude higher than that of the plate-anode reactor. The experiments applying varied water flow rates and discharge currents indicated that the condition tha...

Decomposition of Organic Compounds in Water by Direct Contact of Gas Corona Discharge: Influence of Discharge Conditions

Water purification experiments to decompose phenol, acetic acid, and Rhodamine B in water were conducted using a direct contact of gas corona discharge to the water surface. It was shown that O2 was important in the gas phase for the degradation process, and the negative corona showed higher degradation rates than the positive corona. It was found that the organic contaminants can effectively be decomposed by the present method without pH adjustment. The experimental results indicated that there were optimized values in the O2 concentration, the gas resident time above the water, and the cathode−anode gap. It was also indicated that the O2/CO2 mixture showed a higher degradation rate than the O2/N2 mixture for the gas phase. As the degradation mechanism, the uncharged short-lived radicals are considered to be important.

気相コロナ放電の直接照射による染料溶液の分解処理

Experiments were conducted to decompose three dyes, rhodamine B, methylene blue and erythrosine, in water using a reactor with a gas corona discharge. In this reactor, the gas corona discharge was contacted with the treated water to supply short-lived radicals and ions directly to the water surface, resulting in the production of aqueous reactive species. It was found that these dyes were degraded by this method. Total organic carbon which was not significantly decreased by ozonation without pH control was also decreased by the present method. The decomposed compounds seem to be oxidized to CO2 as final products.

Recent advances in partial discharge measurement capabilities at NIST

Three techniques for measuring the properties of partial discharges (PDs) are described. The first is concerned with an advanced, real-time PD measurement system that allows a complete characterization of the stochastic properties of PD. With this system it is possible to measure a set of conditional PD pulse-amplitude and pulse-time separation distributions from which memory effects characteristic of the discharge phenomena can be quantified and interpreted. Results for pulsating negative corona discharges in gases are shown. The second technique allows PD location in cables using time-domain reflectometry with appropriate statistical analysis. With the third technique, simultaneous measurements are made of the optical and electrical characteristics of PD in liquid dielectrics using fast photography combined with broadband. low-noise pulse current measurements. >

EHD study of the corona wind between wire and plate electrodes

The corona wind, with a velocity of several meters per second, is caused by applying high electric tension to bring about corona discharge in gases. In this paper the corona wind is experimentally and theoretically analyzed from an electrohydrod ynamical (EHD) standpoint. Experiments have been performed mainly in nitrogen by a two-dimensional electrode arrangement of a fine wire anode and a plate cathode. The voltage-current characteristics of an electrostatic probe indicate that positive ions predominate in the whole space except in an extremely narrow region close to the wire. A theoretical analysis has been conducted based on the model that positive ions produced by ionization near the wire electrode move toward the plate, introducing the bulk convective motion of neutral molecules as the result of collisions of ions and neutral molecules. The electric potential distribution in the space and pressure distribution on the plate calculated numerically agree well with the experimental data. Consequently, it is made clear that the corona wind is caused by the Coulomb force exerted on ions and collisions of ions and neutral molecules of gas.

Convective heat-transfer enhancement by electric fields

A general problem is formulated of electroconvective heat transfer and the problems of this kind are classified according to motive force types and to nonuniformity of electrophysical parameters. Typical cases of nonuniformities are considered, namely, thermal, mechanical and those due to the electric field itself. A qualitative theory is developed covering all the flow patterns which correlates experimental data on electroconvective heat transfer in homogeneous and disperse media and on corona discharge in gases. Experimental data agree with theoretical predictions.

Positive and Negative Point-to-Plane Corona in Pure and Impure Hydrogen, Nitrogen, and Argon

To extend knowledge concerning the positive and negative point-to-plane corona, studies were made of the discharge in very pure ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and A. Neither pre-onset streamers nor burst pulses were observed in pure ${\mathrm{H}}_{2}$ and ${\mathrm{N}}_{2}$, in accordance with present theories of these effects. At high fields weak streamers developed which ultimately led to breakdown. Adding traces of ${\mathrm{O}}_{2}$ to either ${\mathrm{H}}_{2}$ or ${\mathrm{N}}_{2}$ at once produced weak pre-onset streamers, and at higher concentrations produced burst pulses. Trichel pulses, which occur in properly triggered corona discharges in gases which form negative ions, are not observed in pure ${\mathrm{H}}_{2}$ and ${\mathrm{N}}_{2}$ but are immediately produced upon the addition of traces of ${\mathrm{O}}_{2}$. For these gases the potentials for negative corona were observed to be lower than for the positive corona. In the case of argon, it was found that with positive point potential the first streamer formed was intense enough to cause spark breakdown, while with the point at a negative potential a heavy arc replaced the corona. Contamination of the argon with ${\mathrm{H}}_{2}$ or ${\mathrm{N}}_{2}$ introduced streamers for the positive corona which showed all the characteristics of those formed in air. This effect is attributed to the suppression of metastable atoms in the argon due to the presence of the impurity. For the negative corona small amounts of these gases (0.1 to 0.5 percent) prevented arcing and yielded a strong corona with glow discharge characteristics but no Trichel pulses. Addition of sufficient ${\mathrm{O}}_{2}$ causes argon to act in all respects like air except that the onset potentials were much lower than in air. A clean-up of impurities in the negative corona in ${\mathrm{H}}_{2}$ is shown to be due to formation and absorption of water vapor. The etching of negative points in the discharges in pure gases appears to be related to the sputtering process.