Corona Discharge In Air Research Articles

Conditions for inception of positive corona discharges in air

Conditions for inception of dc corona discharges in air near spherical and cylindrical anodes are considered. The parameter K (ionization integral) in the standard discharge inception criterion is evaluated for a wide range of electrode radii and air densities.

Negative corona, glow and spark discharges in ambient air and transitions between them

Obtaining new information about different forms of self-sustained dc discharges that can be realized in pin-to-plane electrode geometry in ambient air is the goal of this paper. Experimental and numerical calculation data uncovering the physics of the temporal and spatial evolution of the negative corona and glow discharge (GD), with increase in current up to the transition to the spark, are presented. Special attention is paid to the properties of diffusive GD at atmospheric pressure, which is a necessary stage (steady-state or transient) preceding the spark and determining the threshold conditions of sparking.

On line pd measurements and diagnosis on power transformers

On line partial discharge (PD) measurements provide information on the dielectric integrity of the high voltage insulation of oil insulated power transformers during service. These PD measurements are performed using a broadband antenna on an oil valve and UHF detection of PD signals. The sensitivity of this new detection technique is high and immunity for electromagnetic (EM) interference and corona discharges in air outside the transformer is very good. Dielectric faults can be detected in this way in an early stage of development and are classified in four categories. Automatic pattern recognition techniques of phase resolved pulse sequence (PRPS) data are very useful in risk assessment of dielectric faults.

The Formation, Role and Removal of No3-N During Corona Discharge in Air for Phenol Removal

Pulsed corona discharge carried out in the gas phase has been shown to be a low cost solution for wastewater treatment. In this study, the results show that the nitrogen dissociated during corona discharge in the gas phase formed nitric acid in solution, which resulted in a drop in solution pH. The phenol removal could be described in accordance with a first-order reaction in a basic buffer solution, but not in initial neutral and basic non-buffered solutions. This indicates that basic conditions facilitate phenol removal, whilst the formation of nitric acid in solution resulted in decrease in the phenol removal rate. This study also shows that most of the oxidants used for phenol removal came mainly from the dissociation of water molecules at the surface of the liquid phase and / or the gas phase very close to the liquid surface in discharging conditions, not from the gas dissociation in the bulk gas phase, and therefore, it is more effective to keep the solution basic than to change the component of gas in the reactor when removing phenol from water using corona discharge.

Diagnosis of OH Radical by Optical Emission Spectroscopy in Atmospheric Pressure Unsaturated Humid Air Corona Discharge and its Implication to Desulphurization of Flue Gas

OH radical in the corona discharge with pipe–nozzle–plate electrode has been diagnosed by optical emission spectroscopy. Spatial variations of OH radical emission in discharge gap have been measured. Relative intensity of OH radical emission spectroscopy increases with increasing water vapor flux injected into the reactor or intensity of electric field supported. In positive pulsed corona discharge, relative intensity is higher than that in positive DC corona discharge and lower than that in negative DC corona discharge. Strongest intensity of OH radical spectrum appears within the range of 5 mm near the discharge nozzle- electrode. In addition, it is proved that the efficiency of desulphurization from flue gas by pulsed corona discharge plasma processes can be improved when OH radical is produced in the reactor.

Using an optical fibre anemometer to measure the speed of the electric wind in a negative polarity, atmospheric corona discharge

Coronas are partial discharges that occur in regions of non-uniform electric fields adjacent to conductors stressed to high voltages. Negative, Trichel-pulse coronas in air occur when a dc, negative-polarity, high voltage is applied to a conductor. Trichel pulses in atmospheric air generate significant amounts of ozone as well as electrical and acoustic noise. Under the right conditions these coronas can be a precursor to complete electrical breakdown of the air gap due to a reduction in the density of neutral molecules resulting from a combination of localised heating and convective air flow generated by the movement of negative ions. An optical fibre anemometer, based on a Mach-Zehnder interferometer has been constructed to measure the speed of the wind generated in the point-plane gap of a negative, Trichel-pulse corona discharge in atmospheric air. The sensing arm of the fibre interferometer is subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localised heating and convective cooling by the corona wind results in fringe shifts which are directly calibrated to the speed of the wind. This paper reports on the nature of the calibration process and presents some radial profiles of wind speed in the corona gap.

Electrostatic force measurements in positive unipolar wire-to-plane corona discharges in air

Measurements of electrostatic force generated in the drift region of a positive unipolar wire-to-plane corona discharge in air are compared with numerical simulations. The generated force does not depend on the ion mobilities, preventing the influence of uncertainty and variation of these parameters. A method is described to simulate the voltage and charge distribution for a wire-to-plane set-up. This method enables the determination of the transition between unipolar and bipolar discharges. In the experimental set-up breakdown electric field of air reduces with increasing discharge current.

Surface degradation and hydrophobic recovery of polyolefins treated by air corona and nitrogen atmospheric pressure glow discharge

AbstractThe surface degradation and production of low molecular weight oxidized materials (LMWOM) on biaxially oriented polypropylene (BOPP) and low‐density polyethylene (LDPE) films was investigated and compared for two different dielectric barrier discharge (DBD) treatment types, namely air corona and nitrogen atmospheric pressure glow discharge (N2 APGD). Contact angle measurements, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) analyses were performed in conjunction with rinsing the treated films in water. It is shown that N2 APGD treatments of both polyolefins result in much less surface degradation, therefore, allowing for a significantly higher degree of functionalization and better wettability. Hydrophobic recovery of the treated films has also been studied by monitoring their surface energy (γs) over a period of time extending up to several months after treatment. Following both surface modification techniques, the treated polyolefin films were both found to undergo hydrophobic recovery; however, for N2 APGD modified surfaces, γs ceases to decrease after a few days and attains a higher stable value than in the case of air corona treated films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1291–1303, 2004

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)

An analysis of mass spectrometric study of negative ions extracted from negative corona discharge in air

In this paper we report the detection and mass analysis of negative ions formed in a negative corona discharge using both dry and ‘wet’ air at pressures between 5 and 27kPa. The yield of individual ions is strongly affected by trace concentrations of ozone, nitrogen oxides and water vapour. In dry air the dominant ion is CO3−. In presence of water this is converted very efficiently to cluster ions containing one and more water molecules. If ozone and nitrogen oxides are added, or are produced in discharge in sufficient concentrations, NO3− ions and NO3− hydrated clusters are formed. Ozone concentrations greater than 25ppm are sufficient to completely suppress the appearance of O2− ions and its clusters both in dry and wet air. Such observations allow a comprehensive review of the physical and chemical processes within the discharge.

Corona discharge influences ozone concentrations near rats.

Ozone can be produced by corona discharge either in dry air or when one electrode is submerged in water. Since ozone is toxic, we examined whether ozone production by corona near laboratory animals could reach levels of concern. Male rats were exposed to a corona discharge and the concentration of ozone produced was measured. The resulting concentration of ozone ranged from ambient levels to 250 ppb when animals were located 1 cm from a 10 kV source. Similar ozone concentrations were observed when a grounded water source was present. Possible explanations for, as well as concerns regarding, ozone production under these conditions are discussed.

Inception behaviour of pulsed positive corona in several gases

The inception probability and the streamer length of pulsed positive corona discharges is determined in argon, nitrogen, oxygen and air. This study is performed in a 25 mm point-plane gap at a pressure of 1 bar. The lowest voltage at which a discharge in argon starts is 3 kV but only with an inception probability of 1%. At 5 kV the corona discharge in argon transforms into a spark with a probability close to 100%. The inception probability of corona discharges in all molecular gases used here as a function of the voltage is identical, starting with 1% at 4 kV and going up to 100% at 9 kV. The streamer lengths are quite different for these gases, nitrogen requiring the lowest voltage for streamers to cross the gap and oxygen the highest. This is probably due to electron attachment in oxygen. A remarkable result is that in air streamers bridge the gap at 8 kV, but spark breakdown occurs only above 26 kV. This property makes it relatively easy to obtain powerful pulsed corona discharges in air.

Shape of the current tube of a negative point-to-plane corona in air

Results are presented from the experimental studies of a negative point-to-plane air corona discharge with controlled geometry. It is shown that, in a certain range of parameters, the steady-state current-voltage characteristic of the corona can be fitted by a parabola. The results obtained are used to determine the time-averaged shape of the current tube of a negative corona.

Electrical study of DC positive corona discharge in dry and humid air containing carbon dioxide

As most part of the industrial effluents contain carbon dioxide and water vapour, it is interesting to study from an electric point of view ‘basic’ gas mixtures including air and various amounts of these gases, in order to precise how the corona discharge inception takes place in such mixtures. In a DC point-to-plane reactor, distinct parameters are varied, such as discharge current, partial pressure of CO2, and relative humidity. Gap voltage and streamer frequency are experimentally measured as functions of the discharge current. Current waveforms are recorded in various gas mixtures and electrical conditions. DC and impulsional current components, as well as streamer frequency are also plotted as functions of the CO2 partial pressure for dry and water saturated mixtures. For dry or wet mixtures, 5% CO2 in volume appears to be the proportion allowing the establishment of a stable corona discharge with the lowest energy cost.

Surface composition analysis of PP films treated by corona discharge

Polypropylene films (PP) surface treated by corona discharge in air was analyzed to verify the changes on surface composition. The presence of oxidized polar groups on the film surface, mainly, C=O, C-O and COH, was confirmed by infrared spectroscopy (FTIR/ATR) and atomic force microscopy (AFM) revealed a dramatic change in the morphology and provided qualitative results of the chemical composition (new structures). Contact angle (q) of the PP films decreased after corona treatment indicating an increase in the wettability due to the polar groups formed. Extended treatment results of low molecular weight oxidized material into the surfaces and a smaller additional degree of modification in the wettability is obtained.

About the significance of pd measurements in liquids

This paper presents investigations concerning the variations and significance of PD measurements in mineral oil, when detectors with different frequency response are used. Typical durations of discharge phenomena in liquids are much longer than in other media, and the measurement technique must be adapted accordingly. However, depending on the application concerned, this is not always possible. In this study, experiments and calculations are carried out to determine typical errors produced when classical RLC measurement impedances with various frequency responses are used to measure PD's in liquids. Experiments are done with corona and creeping discharges in mineral oil, and compared with corona and spark discharges in air. These examples allow us to conclude that when a calibrated high frequency PD measurement system is used, the ratio of measured to actual charge is much lower for discharges in liquids than in gases. If measurements are carried out on a practical device that may include various types of PD sources, the high frequency measurement system will strongly underestimate discharges in liquids compared to other discharge types. This discrepancy versus discharge type increases when the frequency response of the measurement system is increased.

Electric wind characterisation in negative point-to-plane corona discharges in air

In point-to-plane corona discharges in air, the collisions of charged particles with neutral particles induce a gas movement between the point to the plane called electric wind. A one-dimensional model of the neutral particle velocity along the discharge axis and between the electrodes is first developed. Laser Doppler Anemometry is used to measure the axial velocity profile of the gas between the electrodes. Discrepancies between experimental results and predictions of the on-axis velocity are discussed. Finally, the measured velocity profile compares quite well with a cos 5 θ distribution. Significant differences between measured and cos 5 θ profiles are observed near the discharge axis which could be attributed to the presence of seeding particles.

Positive and negative gas-phase ion chemistry of chlorofluorocarbons in air at atmospheric pressure.

This paper presents a report on the ionization/dissociation of some representative chlorofluorocarbons (CFCs) induced by corona discharges in air at atmospheric pressure. Both positive and negative ions formed from Freons 1,1,1-trichlorotrifluoroethane (CFC 113a), 1,1,2-trichlorotrifluoroethane (CFC 113), and 1,1,1,2-tetrachlorodifluoroethane (CFC 112a) were analyzed using an atmospheric pressure chemical ionization mass spectrometry (APCI-MS) instrument. Energy-resolved mass spectra were obtained by modulating the kinetic energy of the ions via adjustment of the sampling cone potential (V(cone)). Positive ion spectra of the CFCs (M) at low V(cone) show no signals due to either M(+)* or MH(+) but only those due to species [M - Cl](+) and CX(3)(+) (X = Cl, F), likely formed via C-Cl and C-C bond cleavages following ionization via charge exchange. Charge localization in the products of C-C bond cleavage in M(+)* is driven by the stability of the neutral fragment. At low V(cone) the hydrates [M - Cl](+)(H(2)O) are also observed. In the case of 1,1,2,-trichlorotrifluoroethane, [M - F](+) species also form as a result of ion-molecule reactions. As V(cone) is increased collision-induced dissociation of [M - Cl](+) and [M - F](+), i.e., the perhalogenated cations C(2)X(5)(+) (X = Cl, F), takes place via carbene elimination. In some cases such elimination is preceded or accompanied by rearrangements involving transfer of halogen from one carbon to the other. Evidence is also presented for the occurrence of a condensation reaction of C(2)Cl(3)F(2)(+) with water to form a C(2)Cl(2)F(2)HO(+) species via elimination of HCl. Negative ion spectra are dominated by Cl(-) and its ion-neutral complexes with M and with water. Additional components of the plasma include ion-neutral complexes O(3)(-)(M), the molecular anion M(-) (observed only with 1,1,2-trichlorotrifluoroethane), and an interesting species corresponding to [M - Cl + O](-). The origin and structure of these [M - Cl + O](-) species are discussed in terms of available thermochemical and reactivity data and current mechanistic views concerning reaction of O(2)(-) with halogenated compounds. The observation of both positive and negative ions containing oxygen is of special relevance to development of new processes for the treatment of volatile organic compounds (VOCs) based on oxidative decomposition induced by corona discharges in air at room temperature and pressure.

Theoretical and experimental investigation of a pulsed ESP

The superiority of hybrid pulsed-power/direct-voltage precipitators over conventional designs is now well accepted. In order to maximise the collection efficiency of these devices, a better knowledge of the free-ion charge density and the variation of the inter-electrode electric field is needed. This paper presents the results of an experimental investigation and a theoretical simulation of negative corona discharge in air, under the application of pulsed energisation to a bench-scale coaxial electrode configuration. The construction of the experimental apparatus developed for the present study is described. Corona space charge injection and collection are quantitatively investigated under controlled operating conditions of applied voltage magnitude and frequency. The experimental results obtained are used to verify a new corona model that provides quantitative information regarding corona space charge magnitude and collection time, and can account for the effect of electrode dimensions. The model also quantifies the interdependence of corona discharge parameters including the magnitude of direct and impulse voltage components, impulse frequency and space charge and electric field distributions. This yields the magnitude of important parameters such as the frequency of applied voltage for maximum collection, and the minimum direct voltage level required to prevent corona ions from flowing back to the corona wire.

Chemical kinetics with electrical and gas dynamics modelization forNOx removal in an air corona discharge

A non-stationary reactive gas dynamics model in a mono-dimensional geometry, including radial mass diffusion, gas temperature variation and chemical kinetics, is developed in this paper. The aim is to analyse the spatio-temporal evolution of the main neutral species involved in a corona discharge used for NO pollution control in polluted air at atmospheric pressure and ambient temperature. The present reactive gas dynamics model takes into account 16 neutral chemical species (including certain metastable species) reacting following 110 selected chemical reactions. The initial concentration of each neutral species is obtained from a 1.5D electrical discharge model. The gas temperature variations are due to direct Joule heating during the discharge phase, and also result from the delayed heating due to the relaxation of the vibrational energy into a random thermal energy during the post-discharge phase. The simulation conditions are those of an existing experimental setup (anode voltage of 10 kV in the case of a point to plane geometry with an interelectrode distance of 10 mm). The obtained results show that the diffusion phenomena and the gas temperature rise affect quite well the gas reactivity and the neutral species evolution. This allows us to better understand the different reaction processes and transport phenomena affecting the NO concentration magnitude inside the discharge channel.