Back Discharge Research Articles

Numerical simulation of back discharge ignition

Back discharge refers to any discharges initiated at or near a dielectric layer covering a passive electrode (Czech et al 2011 Eur. Phys. J. D 65 459–74). Back discharge activity is commonly observed in electrostatic precipitators. This study aims to contribute to increasing the fundamental understanding of back discharge phenomena by using a plasma fluid model. The modelling strategy only considers the region of back discharge development as a first approach, and the numerical simulation is complemented by an experimental study. Back discharge ignition is studied with a pinhole of radius 100 µm set in a dielectric layer. First, we have considered the criterion for back discharge ignition from an electrostatic point of view, and the numerical results confirm the major role of the surface charge density deposited on the dielectric layer. Then the dynamics of back discharge in the ‘onset-streamer’ regime (Masuda and Mizuno 1977/1978 J. Electrostat. 2 375–96) is described: the discharge ignites inside the pinhole, develops outside as a cathode-directed ionizing wave, before stopping. This regime is characterized by a current pulse and the corresponding optical emission. Results obtained in experiments and simulations are in good agreement. Furthermore, this discharge regime is independent of the pinhole radius (ranging from 75 to 150 µm) despite a change in the discharge shape. Finally, an increase in the initial negative ion density or Laplacian electric field is found to be responsible for the transition from ‘onset-streamer’ to ‘space streamer’ regime, which corresponds well with experimental observations.

The Effect of Non-Return Nalve on Micro Injection Molding Machine

The micro injection molding machine (MIMM) is used to produce precision plastic products. The non-return valve (NRV) on the screw head of injection machine plays the role of preventing the melt back discharge during injection process. The sensitivity of non-return valves opening and closing affects the quality of the product. In this paper, numerical simulation of three-dimensional flow field is generalized by the Newtonian isothermal fluid method. Then, five kinds of different structural parameters of NRV are designed, and the pressure field, the pressure difference is simulated by the Polyflow software. At last, the pressure field, and the pressure difference on both side of NRV are analyzed and compared. The best structure parameter of NRV is decided. The simulation results are useful for the NRV design.

Studies of corona and back discharges in carbon dioxide

Results of spectroscopic investigations and current-voltage characteristics of corona and back discharges generated in point-plane electrode geometry in CO2 at atmospheric pressure for positive and negative polarity of the discharge electrode are presented in the paper. Three forms of back discharge, for both polarities, were investigated: glow, streamer and low-current back-arc. To generate the back-discharges for the conditions similar to electrostatic precipitator, the plate electrode was covered with fly ash layer. In order to characterize back discharge processes, the emission spectra were measured and compared with those obtained for normal discharge, generated in the same electrode configuration but without the fly ash layer on the plate electrode. The measurements have shown that optical emission spectral lines of atoms and molecules, excited or ionised in back discharge, depend on the forms of the discharge, the discharge current, and are different in the zones close to needle electrode and fly ash layer. From the comparison of spectral lines of back and normal discharges, an effect of fly ash layer on discharge characteristics and morphology has been determined. In normal corona, the emission spectra are mainly predetermined by the working gas components, but in the case of back discharge, the atomic and molecular lines, resulting from chemical composition of fly ash, are also identified. Differences in the spectra of back discharge for positive and negative polarities of the needle electrode have been explained by considering the kind of ions generated in the crater in fly ash layer. For back arc, the emission of spectral lines of atoms and molecules from fly ash layer can be recorded in the crater zone, but in the needle zone, only the emission lines of CO2 and its decomposition products (CO and C2) can be noticed. The studies of back discharge in CO2, as one of the main components of flue gases, were undertaken because this type of discharge, after unwanted inception, decreases the energy and collection efficiencies of electrostatic precipitator. The second reason behind these studies is that CO2 is the main component of flue gas leaving oxyfuel boiler that re-circulates in the combustion-precipitation cycle. It was shown that discharges in CO2 lead to contamination of discharge electrode with carbonaceous products that can cause severe maintenance problems of electrostatic precipitator. The recognition of the characteristics of electrostatic precipitator operating in the oxyfuel system is, therefore, of crucial importance for exhaust gas cleaning in modern combustion systems.

Non-thermal plasma generation by using back corona discharge on catalyst

This paper discusses a novel plasma catalysis generation method based on back-corona discharge along porous catalyst bed reactor. The reactor consists of a high-voltage needle electrode, one floated mesh electrode, one catalyst bed and one grounded mesh electrode. Typical plasma current density is 11.88 μA/cm 2 . It can be used for ozone generation and volatile organic compounds decomposition. By using a home-made AgMnO x /Al 2 O 3 -1 catalyst, 90% of toluene is removed at the specific plasma energy density of 123 J/L. At the same time, aerosol byproducts are collected and then decomposed on the catalyst bed. Moreover, the catalyst is regenerated because of the back-corona discharge.

Corona and back discharges in flue-gas simulating mixture

Abstract Results of spectroscopic investigations and current–voltage characteristics of electrical discharges between a needle and plate electrodes in a gas mixture simulating flue gases from coal fired power plants at atmospheric pressure are presented in the paper. In these investigations, back discharge was generated at the plate electrode covered with fly ash layer in order to simulate the conditions similar to those in electrostatic precipitators. To characterize the physical processes in back discharges, the emission spectra were measured and compared with those obtained for normal corona discharge generated in the same electrode configuration but with fly ash removed from the electrode. The emission spectra provide information on elemental and molecular composition of the layer. It was also shown that discharge characteristics in flue gas are quite different from those occurring in ambient air.

Initiation mechanism of a positive streamer in pressurized carbon dioxide up to liquid and supercritical phases with nanosecond pulsed voltages

In this work, the initiation process of an electrical discharge in pressurized carbon dioxide up to the liquid and supercritical phases was investigated using Schlieren and photomultiplier techniques. A pulsed positive voltage with a rise time of about 40 ns and half-width of 150 ns was applied to a point-to-plane gap. The experimental results showed that the discharge started with a primary streamer consisting of a burst primary streamer and a successive primary streamer, and a back discharge followed them. It was predicted from an analysis of the experimental results that the initiation criterion of a burst primary streamer was electron multiplication on the order of 108 independent of the medium conditions. That is, a direct ionization process without bubble formation is supported as an initiation mechanism of nanosecond positive discharges in pressurized carbon dioxide. The medium state in the burst primary streamer channel was a gas or pseudo-gas of 50–200 kg m−3 density.

Optical emission spectroscopy of point-plane corona and back-corona discharges in air

Results of spectroscopic investigations and current-voltage characteristics of corona discharge and back discharge on fly-ash layer, generated in point-plane electrode geometry in air at atmospheric pressure are presented in the paper. The characteristics of both discharges are similar but differ in the current and voltage ranges of all the discharge forms distinguished during the experiments. Three forms of back discharge, for positive and negative polarity, were investigated: glow, streamer and low-current back-arc. In order to characterize ionisation and excitation processes in back discharge, the emission spectra were measured and compared with those obtained for normal corona discharge generated in the same electrode configuration but with fly ash layer removed. The emission spectra were measured in two discharge zones: near the tip of needle electrode and near the plate. Visual forms of the discharge were recorded with digital camera and referred to current-voltage characteristics and emission spectra. The measurements have shown that spectral lines emitted by back discharge depend on the form of discharge and the discharge current. From the comparison of the spectral lines of back and normal discharges an effect of fly ash layer on the discharge morphology can be determined. The recorded emission spectra formed by ionised gas and plasma near the needle electrode and fly ash layer are different. It should be noted that in back arc emission, spectral lines of fly ash layer components can be distinguished. On the other hand, in needle zone, the emission of high intensity N2 second positive system and NO γ lines can be noticed. Regardless of these gaseous lines, also atomic lines of dust layer were present in the spectrum. The differences in spectra of back discharge for positive and negative polarities of the needle electrode have been explained by considering the kind of ions generated in the crater in fly ash layer. The aim of these studies is to better understand the discharge processes encountered in electrostatic precipitators.

Back-Corona Discharge Phenomenon in the Nonthermal Plasma System

So far, there have been many types of nonthermal plasma systems (as plasma reactors) presented. The main problems in construction of the plasma reactors are relatively low discharge intensity and relatively high pressure drop between their inlets and outlets for proceeding gas. These drawbacks can be eliminated using back-corona discharge phenomenon in the discharge system. Back discharges could be successfully applied in the plasma reactors because of higher discharge (plasma) density and similar pressure drop in comparison to corona discharge systems. Images of plasma from corona discharge and back discharges for a point-to-plane electrode system in the air are presented.

Development of Pulsed Discharge Inside Bubble in Water

The development of pulsed discharges inside a stationary air bubble in water was observed using an intensified charge-coupled device camera with high-speed gate. The discharges were ignited from a tungsten wire inserted into a glass tube, which was immersed in the purified water. The pulsed high voltage was applied to the wire by an inductive energy storage system pulsed-power generator. The streamer discharge was propagated into the bubble from the wire tip with a propagation velocity of 0.5 mm/ns. A back discharge was observed due to a charge accumulation on the water surface and the glass tube.

Observation of Surface Discharge in Nitrogen Based on Pockels Effect

Surface discharge phenomena on dielectric materials in nitrogen are investigated by Pockels effect technique. A needle-plate electrode system is adopted, and one single cycle of 20-Hz sinusoidal HVac is applied with an amplitude of 5 kV. It is found that positive discharges have two distinct regions, i.e., surface charges appear uniformly in a core region, and then, they develop into streamer pattern away from the core. Negative charge distribution always extends uniformly, and when negative voltage returns to zero, back discharge phenomena can be seen clearly. Within pressure decreases from 101 to 21 kPa, the scale of discharge area, the branch width, and the numbers of streamers increase, but charge densities reduce. It is interesting that the products of core region's radius of positive discharges and corresponding pressure are all around 80 torr ×cm.

Non-thermal plasma reactor with back corona discharge electrode

The new design of plasma reactor with back discharge electrode is presented and characterized. The laboratory scale plasma reactor was constructed in a plane parallel geometry with a gas permeable low-field electrode system. The low-field electrode was covered with a dielectric layer enabling the appearance of back corona discharges. The total volume of the reactor is equal to 2 dm3.The discharge properties of the reactor operating at dc voltage in air under normal conditions are given. The results of optimizing the electrical properties are also presented. The influence of back discharges on the discharge current is discussed. The maximum discharge current density obtained during the experiment was equal to about 25 μA/cm2.

Electric field and charge distribution in back discharge in point-plane geometry

The paper presents experimental and theoretical investigations of electric field and charge distribution on the fly-ash layer covering the plate electrode in the back discharge in point-plane geometry. Two kinds of dielectric layer were used in the experiments: highly resistive fly-ash from an electrostatic precipitator and a dielectric plate (PET) with a small pinhole.

Turning polymer foams or polymer-film systems into ferroelectrets: dielectric barrier discharges in voids

Polymer foams and void-containing polymer-film systems with internally charged voids combine large piezoelectricity with mechanical flexibility and elastic compliance. This new class of soft materials (often called ferro- or piezoelectrets) has attracted considerable attention from science and industry. It has been found that the voids can be internally charged by means of dielectric barrier discharges (DBDs) under high electric fields. The charged voids can be considered as man-made macroscopic dipoles. Depending on the ferroelectret structure and the pressure of the internal gas, the voids may be highly compressible. Consequently, very large dipole-moment changes can be induced by mechanical or electrical stresses, leading to large piezoelectricity. DBD charging of the voids is a critical process for rendering polymer foams piezoelectric. Thus a comprehensive exploration of DBD charging is essential for the understanding and the optimization of piezoelectricity in ferroelectrets. Recent studies show that DBDs in the voids are triggered when the internal electric field reaches a threshold value according to Townsend's model of Paschen breakdown. During the DBDs, charges of opposite polarity are generated and trapped at the top and bottom internal surfaces of the gas-filled voids, respectively. The deposited charges induce an electric field opposite to the externally applied one and thus extinguish the DBDs. Back discharges may eventually be triggered when the external voltage is reduced or turned off. In order to optimize the efficiency of DBD charging, the geometry (in particular the height) of the voids, the type of gas and its pressure inside the voids are essential factors to be considered and to be optimized. In addition, the influence of the plasma treatment on the internal void surfaces during the DBDs should be taken into consideration.

Influence of Particle Size, Structure, and Layer Thickness on the Back Discharge in Electrostatic Precipitators

Influence of Particle Size, Structure, and Layer Thickness on the Back Discharge in Electrostatic Precipitators

Laboratory investigations of back discharge in multipoint–plane geometry in flue gases

The paper presents investigations of back discharge occurring in air and flue gases produced by the process of burning of LPG (Liquefied Petroleum Gas) or charcoal at temperature ranging from 20 to 120 °C. The discharge was generated between a charge-emitting multipoint electrode and a plate covered with fly-ash layer. Current–temperature characteristics were determined for this system. The aim of this work was to determine an effect of back discharge on morphology of fly-ash layer and gas composition. It was noticed that flue gases leaving the back-discharge zone contains increased amount of NO x and CO compounds.

Back discharge in multipoint-plane geometry in flue gases

The paper presents investigations of back discharge occurring in air and flue gases produced by the process of burning of liquefied petroleum gas or charcoal. The discharge was generated between a multineedle electrode and plate covered with fly ash layer. The aim of this work was to determine the effects of back discharge in multineedle-to-plate electrode configuration on the fly ash layer covering the plate electrode. Level of NOx and CO emission was also measured. It was found that the chemical composition of flue gas can be changed in the domains where the back discharge occurs, for example, additional amounts of nitrogen oxides (NO and NO2) are produced and also carbon oxide (CO) was produced at higher discharge current.

Spectroscopic investigations of back-corona discharge on fly-ash layer

Results of spectroscopic investigations of back discharge generated in point-plane electrode geometry in ambient air at atmospheric pressure are presented in the paper. The back discharge was generated for the plate electrode covered with fly ash layer. To characterize the discharge process, the emission spectra were measured for the back discharges and compared with those obtained for corona discharge generated in the same electrode configuration but with dielectric layer removed. The measurements have shown that spectral lines emitted by the back discharge depend on the forms of discharge and the discharge current. From comparison of spectral lines of back and normal discharges an effect of the dust layer on discharge morphology can be determined. In normal conditions, the emission spectra are dominated by atmospheric components (molecular nitrogen, atomic oxygen and nitrogen) but for back-discharges, additional lines due to elements and compounds in fly ash were also identified. The studies of back discharge were undertaken because this type of discharge decreases the collection efficiency in electrostatic precipitators.

Corona Discharge and Electrostatic Precipitation in Carbon Dioxide Under Reduced Pressure Simulating Mars Atmosphere

In this paper, the possibility of using electrostatic precipitation (ESP) to clean the gas above solar panels of modules on the surface of planet Mars is investigated. Results are presented on corona discharge in carbon dioxide gas under reduced pressure ranging from 5 to 10 mbar with different electrode configurations. The corona-discharge inception voltage and the threshold of back discharge have been measured for three electrode configurations. The charging of suspended particles of micrometer size in the gas by unipolar ions is examined. Under the considered reduced pressure, diffusion charging very likely dominates over field charging. The drift velocity of charged particles is then estimated and is found to be not drastically lower than in industrial precipitators for fine particles despite the much lower electric field which can be applied under reduced pressure. Finally, the results of a laboratory experiment examining the dust deposit onto photovoltaic cells are presented. It appears that ESP reduces the rate of a Mars analog dust deposit and might be used in order to increase the lifetime of solar panels during Mars missions.

Dust particles motion in back discharge

The back discharge is a type of discharge that takes place in the electrostatics precipitation process, especially in coal-fired power plants for coal of low content of sulfur. This type of discharge takes place in the presence of corona discharge and occurs on an electrode covered with a high resistivity dust layer. The breakdown of dielectric layer causes an increase in the discharge current and re-entrainment of dust particle from collection electrode into the flowing gas. The investigations of the motion of dust particle emitted from the collection electrode are presented in this paper. Additionally, acrylic powder layer placed between a mica plate with a small pinhole and the plate electrode were also used in the experiments in order to generate repeatable back discharge. An effect of back discharge on the collection efficiency in the electrodes system was also presented.

Investigations of DC corona and back discharge characteristics in various gases

The paper presents investigations of forward and back discharges occurring in air, carbon dioxide, and nitrogen, with plate electrode covered with fly ash. For the glow discharge, the back corona current is lower than for normal corona discharge, but for back-arc discharge, both currents are nearly the same. A dielectric layer covering the plate electrode causes that the arc discharge can start at higher voltages. In the arc discharge, the elements present in fly ash can volatilise due to electron bombardment of the layer.