Corona Discharge In Air Research Articles

Charging of Polymeric Surfaces by Positive Impulse Corona

This paper focuses on analysis of charging of polymeric surfaces by means of impulse corona discharges in air. Internal (space charge densities and electric fields) as well as external (circuit current) characteristics of corona in a point-plane electrode configuration are investigated by means of computer simulations. Two types of onset positive corona modes, namely positive glow corona and burst pulse corona are identified. The developed and verified computer model is further used to study corona charging of a 2 mm thick polymeric material sample. Both the mechanism of charge deposition and distribution of deposited charges on the surface are dependent on the mode of the corona discharge used. In the case of glow corona, charge generation is limited to the anode region and the generated charges move towards the sample surface under applied electric field. Thereafter the deposited charge cloud expands radially along a portion of the surface with fairly constant concentration. In the case of burst pulse corona, series of positive charge clouds start from the anode and move towards the sample surface in a wave-like manner. Each burst contributes to the deposited charge, which spreads over the surface less extensively than that observed during glow corona charging.

Implementation of Fuchs' model of ion diffusion charging of nanoparticles considering the electron contribution in dc-corona chargers in high charge densities

A 1D corona discharge model coupled to a 2D-axisymmetric particle charging model are proposed in this paper to simulate nanoparticle charging process within a wire-tube air corona discharge subjected to an applied positive or negative dc voltage. This 1D discharge model provides the distribution of the electric field, the air ion and free electron concentrations for the 2D charging model which in turn solves the spatial distributions of the various charged nanoparticles within the tube. This 2D charging model takes into account the effect of electrons, on the basis of Fuchs' law usually employed in the literature for modelling of ion diffusion nanoparticle charging. The current approach is valid when the concentration of nanoparticles is much lower than the concentration of ionic species in the gas. Numerical results show that the positive air ions can be assumed to be solely responsible for the charging process in a positive air corona charger, while both the negative air ions and electrons play an important role in the negative charging. At high negative charge intensities, the effect of the electrons becomes appreciable due to their high conduction velocity. In general, the numerical results obtained are in good agreement with the experimental data reported in the literature.

Experimental analysis and modelling of positive streamer in air: towards an estimation of O and N radical production

This paper is mainly devoted to the comparison between the calculation and experimental results of primary and secondary streamer development in a point-to-plane positive corona discharge in dry air at atmospheric pressure. The qualitative agreement between experimental and calculation results based on the hydrodynamics approximation shows that the O radical is mainly produced in the secondary streamer which is in good agreement with the recent literature measurements using TALIF diagnostics. However, the O radical production yield (in terms of radicals produced per energy injected) is more efficient in the primary streamer than in the secondary one. The main positive corona discharge characteristics are revisited using fast electrical and optical ICCD and streak camera measurements. The calculation shows two streamer radii of, respectively, 10 µm (associated with the radial extension of a high electron density region) and 200 µm (corresponding to the extension of the radial space charge electric field).

Absorption of Photo‐Ionizing Radiation of Corona Discharges in Air

AbstractThe absorption characteristics of photo‐ionizing VUV radiation emitted by corona discharges in the pressure range from 20 to 750 Torr in dry and humid air were measured. The experimental results are compared with data and approximation formulae obtained by others. For a wide region of pressure and absorption path length, the formula proposed by Zheleznyak et al. (Teplofiz. Vysokih Temp. 1982, 20, 423) seems to be the most reliable for approximation of our results for dry air. We propose a modification of that formula for humid air. The obtained results are suitable for modelling of discharge development in ambient air.magnified image

Molecular Delivery to Cells Facilitated by Corona Ion Deposition

A novel method of inducing the delivery of nonpermeant molecules to the cytosol of cells is presented in this paper. Corona discharge in air was utilized to produce ions that in turn were deposited onto the liquid surface of media containing cultured cells. Murine B16 melanoma cells were used to demonstrate the molecular delivery of fluorescent dye calcein, the drug bleomycin, and a nucleic acid stain SYTOX-green. None of these molecules penetrate cells with intact membranes. Following the corona treatment, cells were observed to admit significant quantities of these molecules from the culture media, relative to control samples. Further, greater than 95% viability of treated cells was observed by Trypan Blue assay. This method may provide an attractive alternative to electroporation where a physical contact between electrodes and cells is needed to deliver molecules to the cytosol.

Primary and Secondary Streamer Dynamics in Pulsed Positive Corona Discharges

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Preliminary comparisons between numerical simulation and experimental results are obtained under pulsed applied voltages in the case of positive point to plane corona discharges in dry air at atmospheric pressure. The experimental conditions correspond to 7 mm interelectrode distances with a tip radius of 20 <formula formulatype="inline"><tex>$\mu\hbox{m}$</tex></formula>. The calculations are based on a first-order 2-D electrohydrodynamic model including the main charged-particle/gas reactions occurring in dry air discharge. The development of the corona discharge is analyzed using streak camera pictures. The transition from the branching structure to the monofilamentary one is described. An interesting comparison is performed between the streak camera pictures and the spatiotemporal evolution of the calculated ionization rate. This shows a qualitative agreement in the development of both primary and secondary streamers. </para>

On the formation and fragmentation of nitrate in mixed clusters using atmospheric pressure corona discharge in air

We report on studies of NO 3 − in mixed clusters of HNO 3 and H 2O, NO 3 −(HNO 3) m (H 2O) n with m = 0–3 and n = 0–300. The ions were formed in a corona discharge in ambient air in the point to plane configuration and investigated in a sector type mass spectrometer. The yields of individual ions depend strongly on the shape of the needle and the needle voltage. An STM needle with a tip radius of around 20 nm, resulted in clusters with m = 2 and 3 and n around 100. After collision-induced dissociation (CID) at 50 keV with Ne gas both positive and negative fragment ions were recorded and unambiguous information about the cluster composition was obtained. Density functional theory (DFT) calculations have been employed to shed light on the experimental findings.

Wyladowania koronowe w powietrzu jako metoda modyfikowania warstwy wierzchniej materialow polimerowych

Wyladowania koronowe w powietrzu jako metoda modyfikowania warstwy wierzchniej materialow polimerowych

Mass spectrometric study of negative ions extracted from point to plane negative corona discharge in ambient air at atmospheric pressure

In this paper, we report the detection and mass analysis of negative ions formed in a negative corona discharge using ambient air at atmospheric pressure. Using a mass spectrometer capable of operating at atmospheric pressure with high sensitivity and excellent mass resolution we have detected many anions that were not observable in earlier studies. Practically all the ions detected were in the form of clusters, mostly containing water, although some clusters containing HNO 3 molecules were observed. In contrast to previous reports a relatively high abundance of O 2 −·(H 2O) n clusters was observed especially when the gap between the two electrodes is small. At larger separations CO 3 −·(H 2O) n , O 3 −·(H 2O) n , NO 3 −·(H 2O) n and HCO 3 −·(H 2O) n cluster were detected with yields between 2 and 10%. Previous work has reported negative ion signal with an amu of 125. In contrast to previous suggestions that this represents OH −·(H 2O) 6 we show that it is a cluster of NO 3 −·HNO 3. Such results demonstrate conclusively that in any atmospheric pressure discharge most of the ion chemistry involves clusters and therefore models and simulation using unimolecular ions in the description of such discharges are liable to serious misinterpretation.

Ozone production by a dc corona discharge in air contaminated by n-heptane

Beneficial purposes of ozone such as elimination of odours, harmful bacteria and mildew can be used for transportation of food, fruits and vegetables with the aim to extend their storage life. To date the main technique used for this purpose in the transportation of these commodities, e.g. by trucks, was cooling. Here a combination of cooling together with the supply of ozone into containers with these commodities is considered. For these purposes we studied the effect of air contamination by n-heptane (part of automotive fuels) and humidity on ozone production by a dc hollow needle to mesh corona discharge.We found that, for both polarities of the needle electrode, addition of n-heptane to air (a) decreases ozone production; (b) causes discharge poisoning to occur at lower current than for air; (c) does not substantially influence the current for which the ozone production reaches the maximum. Finally the maximum ozone production for the discharge in air occurs for the same current as the maximum ozone production for the discharge contaminated by n-heptane. We also found that humidity decreases ozone production from air contaminated by n-heptane irrespective of the polarity of the coronating needle electrode. This dependence is stronger for the discharge with the needle biased positively.

Enhancing the mechanical efficiency of electric wind in corona discharges

This paper deals with experimental measurements of the electric wind velocity induced by corona discharges in air at atmospheric pressure. DC coronas are established inside a tube of a few cm in diameter, between a HV needle and a grounded electrode (grid and ring), in order to produce an electric wind for airflow applications or EHD gas pumps. The goal here is to optimize the corona properties to increase its mechanical efficiency, such as electric wind velocity. The influence of the following parameters is investigated: electrode polarity, collecting electrode geometry, electrode gap and tube diameter. Measurements of time-averaged velocity profiles at the tube outlet have allowed us to compute flow rate, induced mechanical power and efficiency of each configuration. This has shown that: (1) the maximum velocity is higher in the case of positive coronas than in the case of negative ones, (2) this is certainly due to the presence of streamers in the case of positive coronas, (3) mesh size plays a fundamental role and using a grid as a collecting electrode is more efficient than a ring, and (4) the most efficient configuration allowed us to produce a 10 m/s electrical wind, a flow rate of about one l/s, a mechanical power of a few mW with an efficiency of about one percent.

Effect of oxidation on the wettability of poly(dimethylsiloxane) surfaces

The wetting of amorphous poly(dimethylsiloxane) (PDMS) surfaces by water has been studied using molecular dynamics simulations. PDMS surfaces were generated by compressing a long PDMS chain between two elastic boundaries at atmospheric pressure. Oxidation of the PDMS surface, achieved in real systems by exposure to air plasma or corona discharge, was modeled by replacing methyl groups on the PDMS chain with hydroxyl groups. Three surfaces of varying degrees of oxidation were characterized by measuring the water contact angle and the roughness. The dependence of the microscopic contact angle on drop size was measured from time averaged density profiles. The macroscopic contact angle was measured directly using a cylindrical drop of infinite length with zero contact line curvature. The measured macroscopic contact angle ranged from approximately 125 degrees on the untreated surface to 75 degrees on the most oxidized surface studied. The line tension was found to increase with increasing degree of oxidation, from a negligible value on the untreated surface to approximately 5x10(-11) J m(-1) on the most heavily oxidized surface.

Electrical analysis of positive corona discharge in air and N2, O2, and CO2 mixtures

This paper presents an experimental analysis of the electrical behavior of positive point-plane corona discharges. The corona current, streamer velocity, mean discharge frequency, and current-voltage characteristic are studied, firstly in synthetic air as a function of experimental parameters such as gap distance and tip radius. Different electrical diagnostics are used in order to better understand the streamer development as well as the dependence of its characteristics on the previous listed parameters. Then the influence of gas mixture (several proportions of N2 and O2 with or without CO2) is analyzed. When the gas concentration is varied the shape and amplitude of the corona current are significantly affected due to the variation of the gas electronegativity following its composition and concentration. The ionization and attachment coefficients are calculated from the electron energy distribution function in the case of these different gas mixtures in order to quantify the critical electric field value enabling the streamer development for a given gas mixture.

Observation of VUV Emission Spectra from DC Positive Corona Discharge

It has been reported that the experimental investigations on the synchronization probabilities of the two surface streamers in atmospheric air by the authors. This synchronization phenomenon is interpreted by following processes. When an impulse voltage is applied to the parallel connected electrodes, a prior streamer occurs and the propagating streamer emits light. This light passes through the air and reaches the other electrode area. In this area, the initial electrons are supplied by the light and the initial electrons trigger the second streamer. The wavelength region of the light effective for the synchronization was confirmed experimentally. The region was shorter than 250 nm but the detailed wavelength cannot be specified by the experiments. Accordingly, as the first step to specify the effective wavelength, VUV emission spectra from DC positive corona discharges in air are observed together with nitrogen and oxygen gases. Several strong line spectra emitted from the discharges in air are recognized. They are identified that the emission lines of 174 nm, 149 nm and 118 nm are radiated from atomic nitrogen. On the other hand, the emission lines of 120 nm and 130 nm are originated from atomic oxygen. The preliminary experimental results show that these lights are absorbed immediately in air, so on-site photoabsorption measurements were carried out in air. The absorption coefficients of the air are estimated in this study. Even if the wavelength of the light is in the region of VUV, the light can pass through in the air. The facts suggest that the VUV light can pass through long distance in air and the light is effective for the propagation and the synchronization of streamer discharges through the photoelectron emission.

Finite-element analysis of positive and negative corona discharge in wire-to-plane system

This paper deals with positive and negative corona discharge in atmospheric air using a wire-to-plane system. The Poisson's equation is solved numerically using the finite-element method and the current continuity equation. The space charge density is updated using the simplified method of characteristics, where the ion diffusion is neglected. The numerical model takes into account the avalanche length of the corona discharge and the potential corresponding to the minimum ionisation field is directly introduced in the method on the border of the ionisation region. The end geometry of the linear biased probe without wraparound bias plates has been adapted to a wire-to-plane system for use in DC corona discharge. The current density and the electric field are measured; their spatial distributions are given and compared with the computed values. The agreement between the calculated values and those obtained experimentally is satisfactory. The per unit electric field and current density are also represented by a unique function.

A comparative assessment of two optical fibre techniques for measuring the speed of the electric wind in a negative polarity, atmospheric corona discharge**This paper was presented at the 13th International Conference on Sensors and their Applications, held in Chatham, Kent, on 6–7 September 2005.

Two optical fibre anemometers, one based on a Mach–Zehnder interferometer (OFIA) and another a novel laser-optical fibre Bragg grating sensor (FBGA) have been constructed to measure the speed of the convective air flow generated in the point-plane gap of a negative corona discharge in atmospheric air. In both configurations the sensing section of the optical fibre anemometers is subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localized heating and convective cooling by the corona wind results in an optical signal that is directly calibrated to the speed of the wind. Both the OFIA and FBGA successfully measured the speed of the corona wind in the discharge gap, with wind speeds ranging from 0 to 0.7 m s−1 observed at different locations in the discharge gap. However, the FBGA, due primarily to the ability to average sensor response over many measurements, exhibited an order of magnitude higher sensitivity than the OFIA (Δv ≈ 4 × 10−3 m s−1 compared to 3 × 10−2 m s−1). Both sensors yielded measurements of wind speed that were an order of magnitude lower than similar measurements using laser Doppler anemometry (LDA), indicating that the seed particles introduced as part of the LDA system are providing false reading of wind speed due to acceleration by the gap electric field.

Laser-optical fiber Bragg grating anemometer for measuring gas flows: application to measuring the electric wind

A novel laser-optical fiber Bragg grating anemometer (FBGA) has been devised for measuring the speed of a moving gas in the range 0-1.5 m s(-1). As a test, the FBGA was applied to measuring the speed of the electric wind generated in the particularly harsh, high-voltage environment of a dc, negative-polarity, partial (corona) discharge in atmospheric air. The instrument proved more stable and yielded an order-of-magnitude improvement in sensitivity (deltav approximately 4 x 10(-3) ms(-1)) compared with other optical-fiber-based anemometers. On-axis wind speeds ranging from zero to 1.1 m s(-1) were measured in the vicinity of the corona discharge.

Electrohydrodynamic Enhancement of Heat Transfer for Developing Air Flow in Square Ducts

Corona discharge in air was used to generate a secondary flow that significantly improved the convective heat transfer coefficient in the developing region of a square duct. A wire electrode, charged with a high voltage, was placed at the center of the duct. The electrode ionized the air and created a corona current, which was measured experimentally and used in the computations. The conservation differential equations for flow, energy, and electric field were considered for the 3D flow in the developing region of the duct, and they were solved numerically. The computational results indicated that the secondary flow gradually evolves into a fully-developed eight-cell vortical structure that creates flow mixing and turbulence and enhances the heat transfer coefficient. In this study, the ranges of Reynolds number and applied voltage were 500–10,000 and 0–11.7 kV, respectively. The normalized Nusselt number, Nu/Nuo, ranged from 1.06 (Re = 10,000 and 8.1 kV) to 13.58 (Re = 2000 and 11.7 kV), but the pressure drop penalty was relatively low. The normalized friction factor, f/fo, ranged from 1.01 (Re = 10,000 and 8.1 kV) to 7.28 (Re = 2000 and 11.7 kV). The computations were verified by comparison with the published literature.

Measurement of the electro-optic coefficient of polymer thin films with better spatial resolution

A method for measuring the electro-optic coefficient of polymer films on the basis of an asymmetry Fabry–Perot cavity is introduced. The sample layer is located between two aluminium layers, which are deposited on glass substrates by thermal evaporation. This layer structure is objected to a laser beam, and a variable voltage is applied to the aluminium films resulting in a modulation of the transmitted laser power. The electro-optic coefficient γ 13 of the poled polymer film can be calculated by evaluating the Fabry–Perot equation. The spatial resolution is tested with a polymer film that was poled by a needle corona discharge in air through a metal grating with a period of 120 μm. By scanning the sample plate in the direction perpendicular to the grating lines, the spatial resolution is also demonstrated according to the spacing of the poled structure.

Development of a short pulsed corona discharge ionization source for ion mobility spectrometry

The development of a pulsed corona discharge ionization source and its use in ion mobility spectrometry (IMS) is presented. In a point-plane electrode geometry, an electrical pulse up to 12 kV, 150 ns rise time and 500 ns pulse width was used to generate a corona discharge in air. A single positive high voltage pulse was able to generate about 1.6×1010 ions at energy consumption of 22μJ. Since the temporal distribution of ions is in a pulsed form, the possibility of removal the ion gate has been investigated. By purposely arranging the interface between discharge field and drift field, nearly 107 positive ions were drawn into the drift region with absence of the ion gate after every single discharge. The positive spectrum of acetone dimer (working at room temperature) was obtained with a resolving power of 20 by using this configuration. The advantages of this new scheme are the low power consumption compared with the dc method as well as the simplicity of the IMS cell structure.