Negative Corona Research Articles

Design, Fabrication and Mass-spectrometric Studies of a Micro Ion Source for High-Field Asymmetric Waveform Ion Mobility Spectrometry.

A needle-to-cylinder electrode, adopted as an ion source for high-field asymmetric ion mobility spectrometry (FAIMS), is designed and fabricated by lithographie, galvanoformung and abformung (LIGA) technology. The needle, with a tip diameter of 20 μm and thickness of 20 μm, and a cylinder, with a diameter of 400 μm, were connected to the negative high voltage and ground, respectively. A negative corona and glow discharge were realized. For acetone with a density of 99.7 ppm, ethanol with a density of 300 ppm, and acetic ether with a density of 99.3 ppm, the sample gas was ionized by the needle-to-cylinder chip and the ions were detected by an LTQ XL™ (Thermo Scientific Corp.) mass spectrometer. The mass spectra show that the ions are mainly the protonated monomer, the proton bound dimer, and an ion-H2O molecule cluster. In tandem with a FAIMS system, the FAIMS spectra show that the resolving power increases with an increase in the RF voltage. The obtained experimental results showed that the micro needle-to-cylinder chip may serve as a miniature, low cost and non-radioactive ion source for FAIMS.

Closed SDBD-driven two-stage electrostatic precipitator

Recently, the so-called two-stage electrostatic precipitators (ESPs) have again become an object of interest due to their usefulness in efficient collection of PM2.5 particles (of size < 2.5 μm) from polluted air. A two-stage ESP consists of two sections: an air ionisation and particle charging section (called a charging section) and a collecting section for precipitating the charged particles. The ESP has to be equipped with a means for forcing the polluted air to pass through both sections. Various forms of the corona discharges (DC, AC, pulsed) have been used for the air ionisation and particle charging in the first section, while the particle collecting section has usually been electrically supplied with a DC voltage of an amplitude insufficient for the corona discharge onset in this section. In this paper, we propose and present the use of the so-called surface dielectric barrier discharge (SDBD) in the form of an electrohydrodynamic (EHD) actuator as an alternative discharge source in the two-phase fluid (air + particles) of the two-stage ESP, instead of the commonly used corona discharge. Although different in terms of the electrical arrangement, discharge characteristics and morphology, the SDBD can play a similar role as the corona discharge plays in the two-stage ESPs. First, in the two-phase fluid (air + particle) of two-stage ESP the SDBD would be capable of generating bipolar (positive and negative) ions in air, which in turn would charge bipolarly the particles suspended in it. The bipolarly charged particles would agglomerate into larger charged particles, the collection of which is more efficient when subjected to the electrostatic force in the collecting section. Second, the SBDB would induce a unidirectional EHD flow in the two-phase fluid. The EHD flow can either enhance the primary flow of the two-phase fluid or act as a sole flow actuator (rather in relatively small ESPs). The suitability of SDBD for the two-stage ESP systems have been tested in the experiment performed by us using a laboratory-scale closed-volume SDBD-driven two-stage ESP. The experiment comprised measurements of the SDBD discharge characteristics, PTV (Particle Tracking Velocimetry) indirect detecting the production of bipolarly charged particles by the SDBD and then monitoring their trajectories in the collecting section of the SDBD-driven ESP, and qualitative and quantitative studies of the particle removal (or collection) efficiency of the closed SDBD-driven ESP. The PTV monitoring of the particle trajectories was aimed at visualization of the collecting section operation. The experimental results showed that the lab-scale SDBD-driven ESP has proved successful in collecting the particles suspended in air in a closed volume. However, it turned out that the presented lab-scale SDBD-driven ESP was not optimally designed. Despite this, it exhibited the particle removal efficiency similar to that of the single needle-to-plate negative DC corona one-stage ESP, considered as the basic unit for forming larger ESPs. After optimizing the design of lab-scale SDBD-driven ESP unit, we intend to study its performance in flow system, i.e. for the removal of particles from a particle-polluted air stream.

Study on the discharge mechanism and EM radiation characteristics of Trichel pulse discharge in air

The Trichel pulse stage is an unstable stage of negative corona discharge that can also involve electromagnetic (EM) radiation signals. In this paper, the discharge mechanism and radiation characteristics of the Trichel pulse are studied in the needle-plate electrode configuration. The Trichel pulse current and its EM radiation signals are measured at different applied voltages. The results show that Trichel pulse discharge changes from the random pulse stage to the continuous pulse stage as the applied voltage increases. During these different stages, the normalized shape of the Trichel pulses remains unchanged, while the frequency of the EM radiation generated by the discharge remains unchanged. The discharge mechanism and EM radiation characteristics of the Trichel pulse are theoretically analyzed in the different stages. Both the positive ion sheath and the negative ion cloud play key roles in the formation of the Trichel pulse. The EM radiation signal is generated by the rapidly changing Trichel pulse current, and the Trichel pulse current waveform determines the characteristics of the EM radiation signal.

Electret and Dielectric Properties of Lyophilized Polymer Films

Polymer electrets are one of the most important types of electrets, which are widely used both in academic research and industrial applications. The effect of trapped charges on dielectric properties of the polymer electrets is crucial for more intelligent utilization of these materials. The aim of the present paper is to investigate the lyophilization effect on electret and dielectric properties of polymer films. The properties of one synthetic polymer (polystyrene – PS) and two biopolymers (polylactic acid – PDLA and poly-ε-caprolactone – PεC) were investigated and compared. The samples were analyzed by means of dielectric relaxation spectroscopy in the range of 20 Hz – 1 MHz using QuadTech 1910 Inductance Analyzer. The frequency dependences of the impedance magnitude and the phase angle were measured. Regarding the electret properties, the samples were charged in a conventional three-electrode corona system. Positive and negative 5 kV voltage was applied to the corona electrode and 600 V voltage with the same polarity was applied to the grid as to the corona electrode. The results showed that the lyophilization increases time relaxation of the trapped charges. It was established that the samples charged in a positive corona are more stable than those charged in a negative corona.

Mobility of non thermal electrons and ions in very high density and purified nitrogen corona discharge

The mobility of nonthermal electrons and ions have been determined in very high and purified nitrogen corona discharge. Corona discharge was generated by plasma generator system with point-to-plane electrodes geometry configuration. Charateristic I-V has been done by using stabilized DC high voltage generator high up to 20 kV. Graph current of saturation corona unipolar for variation voltage and the distance between electrodes is curved with the semi-parabolic equation. We used I-V characteristic to determine charge patricles mobilities. In this research high purified and slighly purified nitrogen gas. For negative corona, we found that the mobility of charged particles is greater than negative ions and smaller than thermal electron mobility. Particles engaging and moving in the corona with high purification the gas are nonthermal electrons, positive ions for positive corona. From the current-voltage characteristic, we can conclude that the regime of our discharge in very pure gases (N2) corresponds to the current regime limited by space charge. By analogy with what has been observed in a “discharge tube” this regime is similar to an abnormal glow discharge regime. We have seen previously that the variation with the density of the ionic mobility is in good agreement with the direct measurements by the time of flight method.

Kinetics and Products of Air Plasma Induced Oxidation in Water of Imidacloprid and Thiamethoxam Treated Individually and in Mixture

Imidacloprid (I) and thiamethoxam (T) are widely used neonicotinoid insecticides with high persistence in the environment and thus included in the watch list of substances for European Union-wide monitoring reported in the Decision 2015/495/EU. In this work aqueous solutions of I, T and I + T were subjected to advanced oxidation by air plasma produced by negative DC corona discharges above the liquid surface. The oxidative degradation of each pollutant was investigated by monitoring the rate and the products of its decay when treated alone and in the presence of variable amounts of the other compound. The results show that both I and T are readily degraded and that mineralization can be achieved in this process, as proven by the measurement of the residual organic carbon and by the quantitative conversion of chlorine and sulfur into inorganic chloride and sulfate, respectively. The major organic intermediates formed during the complex stepwise oxidation of I and T were identified and monitored by HPLC–MS/MS analysis. The results of kinetic studies show that both for I and T the reaction rate depends inversely on the insecticide initial concentration, that I and T have similar reactivities and that they do not interfere reciprocally in any specific way when treated in mixture at a total concentration of ca 1 × 10−4 M. Based on literature data and on previous results with the same reactor, it is reasonable to propose that the oxidation of I and T is initiated by the reaction with OH radicals.

Effect of gas composition on nitric oxide removal from simulated flue gas with DBD-NPC method

Abstract A new method for nitric oxide (NO) removal was developed by combining dielectric barrier discharge (DBD) and negative pulse corona (NPC). The effects of gas composition (O2, CO2, and H2O) on NO removal were investigated with this method, and the effect of alcohols (methanol and ethanol) addition on NO removal was also investigated as well as the reaction mechanisms to enhance the NO removal efficiency. The experimental results showed that O2, CO2, and H2O had obvious inhibition effects on NO removal, and the negative effects were in the following order: O2 > CO2 > H2O. The addition of methanol or ethanol in the reaction system could mitigate the negative effects of O2, CO2, and H2O on NO removal, and also eliminated the production of NO2. The positive effect of alcohols addition with DBD-NPC denitration method was also validated in the simulated flue gas, in which the NOx (NO, NO2) was mainly converted into N2.

Nitric oxide removal from flue gas using dielectric barrier discharge coupled with negative pulse corona

To optimize the efficiency of nitric oxide (NO) removal, a new catalyst-free method at room temperature was developed by combining dielectric barrier discharge (DBD) and negative pulse corona (NPC). With this method, the effects of applied current, initial NO concentration, gas flow rate, O2 concentration, methanol addition, and the selection of applied current and gas flow rate on NO removal were investigated respectively. Results showed that increasing current not only promoted the NO removal but also reduced NO2 and N2O formation. The NO removal efficiency had a negative dependence on initial NO concentration and gas flow rate. A negative effect of O2 on NO removal was observed, and it also promoted the formation of NO2. However, adding methanol was able to mitigate the negative effects and eliminate NO2 exhaust. The addition of 0.5 vol% methanol raised NO removal efficiency from 30.9% to 98.6% under the condition of 1.67 A, 500 ppm NO, 0.625 L/min with 8 vol% O2 in the flue gas. The reaction path of NO removal process was strongly altered as methanol added into DBD-NPC processing. NOX (NO, NO2) can be reduced to N2 with CH3OH as a reductant. A simple combined denitration method (DBD-NPC) without the assistance of selective catalytic reduction (SCR), additional heating and pressure was developed and evaluated, which may provide potential applications for denitration industry.

Comparison of positive and negative DC discharge under coal pyrolysis gas media at high temperatures

To study the characteristics of positive and negative DC discharge under coal pyrolysis gas media at 20 °C–600 °C, the IV characteristics and the current composition are analyzed under different conditions. Due to the difference of ionization mechanism, the corona onset voltage of negative corona is lower than that of positive corona under air gas medium. Under non-electronegative gas media, no corona occurs during negative discharge. However, during positive discharge, with the increase of output voltage, three types of discharge are successively observed, namely corona, glow and arc. Under N2 gas media and at 400 °C, the maximum collection efficiency of positive electrostatic precipitator is 98%, while that of negative electrostatic precipitator is 82%. When the collection efficiency is 70%, the energy consumption index of negative electrostatic precipitator is about 200 times higher than that of positive electrostatic precipitator. A linear relationship between I/V and V is observed and the ionic mobility can be calculated through the slope. At 350 °C, the ionic mobility under H2 gas medium is 5.25 cm2/(V*s) while the ionic mobility under N2 gas medium is 0.1 cm2/(V*s). The ionic mobility is proportional to the absolute temperature according to the discharge experimental data at 350 °C–600 °C. The factor βi, which is only related to gas media, is 0.0001653 cm2/(V*s*T) for N2 and 0.0087308 cm2/(V*s*T) for H2. These results assist in understanding the property of ESP at high temperatures.

Numerical Simulation of the Trichel-Pulse in SF6 at Atmospheric Pressure

The dynamics of the Trichel current pulses in a dc negative corona in SF6 at atmospheric pressure in a coaxial electrode configuration has been simulated using a self-consistent 1-D model. The aim of this paper was to clarify the role of the plasma charged particles on the ignition and development of the corona Trichel current pulses during the rise time of the applied voltage. The results showed that, during this time, the corona current consists of three sequential pulses with different amplitudes and the first pulse amplitude is larger than the others. It is found that, during the time of the first current pulse, the accumulation of the positive ions near the negative electrode has a main influence on the behavior of the radial electric field distribution and hence on the slow motion of the negative ions toward the ground electrode. This slow motion of the negative ions could play the key role on the next current pulse appearing.

Characteristics of Negative Corona Discharge in Air at Various Gaps

The length of the air gap in a negative corona discharge, which affects many corresponding parameters in the discharge process, is of vital importance for the physical investigations. A hydrodynamic drift-diffusion approximation model considering photoionization utilizing the finite-element method has been used in needle-to-plane air gaps. Trichel pulses, pulse frequency, electron, and electric field distribution, and surface current density distribution on the anode plate were presented to study the effect of the gap length. An approximate exponential relationship was found to exist between the corona current and the gap length, and also a linear function was found between the pulse frequency and the gap length. The analysis shows that the characteristics of the Trichel pulse are strongly dominated by the length of the air gap.

The Effect of Environmental Temperature on Negative Corona Discharge Under the Action of Photoionization

The properties of corona discharge in practical applications are strongly influenced by the variation of environmental parameters. A 2-D axisymmetric hydrodynamic drift-diffusion model coupled with Poisson's equation and three Helmholtz differential equations is established to investigate the effect of environmental temperature on negative corona discharge under the action of photoionization. This numerical model is performed by a traditional needle-to-plane configuration in dry air at atmospheric pressure. The characteristics of Trichel pulses, negative ion density, electric field, and electron density are discussed in this paper. It is found that the magnitude of Trichel pulses, first pulse duration, and pulse frequency increase with increasing the ambient temperature. Moreover, the effect of photoionization under these conditions is also investigated by simulations intensively.

Disinfection by HO2 Radicals Generated by Negative Corona Discharge on Acidic Solution

An oxygen-supplied negative direct current (dc) corona discharge on acidic solution is studied to reduce the odor associated with conventional disinfectants, such as ClO - , HClO, O 3 , and ClO 2 . The discharge system provided an odorless bactericide of hydroperoxyl (HO2) radicals, generated from the reaction of discharge-generated O 2 - with H + in the acidic solution. A 2.5-log reduction of Escherichia coli (E. coli) was observed under the conditions of pH 2.8, dc -4.8-kV dc, and -17 μA, where the concentration of ozone and hydrogen peroxide was too low to inactivate the E. coli. At a pH of 5.6 or by adding a superoxide dismutase, which is a scavenger of HO 2 , negligible inactivation was observed.

Comparison of discharge mechanism of negative corona between hyperboloid and hemispherical electrodes

Electrostatic precipitators based on corona discharge are a research hotspot in recent years. It is of great significance to investigate the characteristics of corona discharge under different system parameters for improving the dust removal efficiency. In this manuscript, the continuity equations coupled with Poisson’s equation are solved by the finite element method (FEM) to explore the different mechanisms of the generation of Trichel pulses when hyperboloid and hemispherical electrodes are used in negative corona discharges for a needle-plate configuration under atmospheric pressure. The fitting curve of the Trichel pulse frequency versus systematic macro parameters, including the applied voltage, the needle tip radius and the needle-plate distance, are given and their mechanisms are analyzed. Subsequently, the features of the Trichel pulses of the hyperboloid electrode and the hemispherical electrode at similar power are compared. From precipitation point of view, the hemispherical electrode is obviously better than hyperboloid electrode.

Experimental Study on Influence of Gas Flow on Trichel Pulse Discharge

Negative corona discharge is the basis of electrostatic precipitator(ESP) which has been widely used in various production fields due to its significant advantages. The characteristics of negative corona discharge have an important impact on dust removel efficiency of ESP. In this paper, the influence of airflow on negative corona discharge has been studied experimentally based on needle-net discharge model which is simplified of ESP discharge electrodes. Using statistical method, the influence of airflow on the parameters of Trichel pulse was analyzed. According to the simulation results of the negative ion desity distribution in the discharge zone by COMSOL software, the reasonable explanation for the experimental results is given.

Pulse Current of Multi-Needle Negative Corona Discharge and Its Electromagnetic Radiation Characteristics

Negative corona discharge occurs widely in high voltage transmission lines and other “high voltage” uses, which can cause strong electromagnetic interference (EMI). In this research, the pulse current of multi-needle negative corona discharge and its electromagnetic (EM) radiation characteristics were studied and compared with that of single-needle negative corona discharge. A dipole radiation model was established to analyze the EM radiation characteristics of the negative corona discharge. The results show that the Trichel pulse discharge process of one discharge needle in multi-needle discharge structure will inhibit the discharge of the other discharge needles. It is only when the voltage reaches a certain threshold will the current and EM radiation fields of multi-needle discharge structure with a significant increasing of amolitude. The frequency of EM radiation of negative corona discharge is not affected by the number of needles, but is only related to ambient air pressure. This research provides a basis for detecting corona discharge sources in different conditions.

Numerical modeling of negative needle‐to‐plane corona in air under various environmental parameters

In this work, an axisymmetric finite element model and a corona discharge measurement system are used to investigate the negative corona discharge process in air under different environmental conditions. The Trichel pulse train, distribution of electron density and electric field, and the electron generation rate are shown. Pulse frequency, critical electric field, and critical electron generation rate are studied at different values of temperature, relative humidity, and air pressure. The results show that the pulse frequency has a strong relationship with the critical electric field and critical electron generation rate. The pulse frequency increases linearly with the ambient temperature and the relative humidity, while it decreases with the air pressure. This numerical model is helpful in better understanding the mechanisms of negative corona discharge under various environmental parameters. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

High Frequency Feature of Pinhole-to-Plate Sinusoidal micro-DBD

The high (∼ GHz range) frequency features of the sinusoidal axi-symmetrical micro-DBD discharge are studied with 2Dt numerical model. It was found that both in the negative and positive driving electrode polarities the electrode current reveals the rather regular “pulse” mode similar to the well-known Trichet pulse structure typically observed in the negative corona discharges in air. The preliminary analyses shown the reason of that is probably the strong nonlinear drift-diffusion-ionization interaction near the electrode surface.

Numerical simulation of negative point-plane corona discharge mechanism in SF6 gas

This paper presents the results of the numerical simulation of negative corona discharge in SF6 at 0.4 Mpa for a point-plane configuration. A 2D axisymmetric model considering three charged species has been investigated with an applied voltage equal to −25 kV. Three drift-diffusion equations coupled with Poisson’s equation were solved simultaneously to obtain the temporal and spatial properties of Trichel pulses. The distributions of charged species at different instants of time and the time-dependent total number of charged species have been determined. The characteristics of current pulses with voltages varying from −24 kV to −27 kV were compared and it has been found that the characteristics of the current magnitude and frequency are similar to those in air. The effects of the model coefficients—the ionization coefficient, the attachment coefficient, the mobility of charged species and the secondary emission coefficient—on the characteristics of current pulses have also been studied to investigate the sensitivities of the pulse parameters to these coefficients.

Comparative Study of AC and Positive and Negative DC Visual Corona for Sphere-Plane Gaps in Atmospheric Air

Due to the expansion of high-voltage direct current (HVDC) power systems, manufacturers of high-voltage (HV) hardware for alternating current (ac) applications are focusing their efforts towards the HVDC market. Because of the historical preponderance of ac power systems, such manufacturers have a strong background in ac corona but they need to acquire more knowledge about direct current (dc) corona. Due to the complex nature of corona, experimental data is required to describe its behavior. This work performs an experimental comparative analysis between the inception of ac corona and positive and negative dc corona. First, the sphere-plane air gap is analyzed from experimental data, and the corona inception voltages for different geometries are measured in a high-voltage laboratory. Next, the surface electric field strength is determined from finite element method simulations, since it provides valuable information about corona inception conditions. The experimental data obtained are fitted to an equation based on Peek’s law, which allows determining the equivalence between the visual corona surface electric field strength for ac and dc supply. Finally, additional experimental results performed on substation connectors are presented to further validate the previous results by means of commercial high-voltage hardware. The results presented in this paper could be especially valuable for high-voltage hardware manufacturers, since they allow determining the dc voltage and electric field values at which their ac products can withstand free of corona when operating in dc grids.