Pulsed Corona Research Articles

Evaluation of pulsed streamer corona experiments to determine the O* radical yield

The production of O* radicals in air by a pulsed streamer plasma is studied by integration of a large set of precise experimental data and the chemical kinetics of ozone production. The measured data comprise ozone production, plasma energy, streamer volume, streamer length, streamer velocity, humidity and gas-flow rate. Instead of entering input parameters into a kinetic model to calculate the end products the opposite strategy is followed. Since the amount of end-products (ozone) is known from the measurements the model had to be applied in the reverse direction to determine the input parameters, i.e. the O* radical concentration.

Decomposition of Methylene Blue in Water by Corona Discharges

The decomposition of methylene blue (MB) in aqueous solution was investigated using a pulsed corona discharge. The discharge was ignited in the gas bubbled in the solution through several needle electrodes. The influence of treatment time, volume of the treated solution and initial concentration of the dye in solution on MB degradation was studied. The effect of the nature of the gas introduced was also investigated. For the same energy input, MB conversion increased in the order air < argon < oxygen. When using oxygen, the decomposition of MB exceeded 95% after ~20 min plasma treatment. Higher efficiency was obtained for higher treated volume and higher initial concentration. At 90% conversion the yield obtained with oxygen was ~5 g/kWh for an initial concentration of 150 mg/l and a treated volume of solution of 100 ml.

Optical properties and chemical behavior of Laser-dye Coumarin-500 and the influence of atmospheric corona discharges

Structure elucidation of Coumarin-500 Laser-dye in cyclohexane at room temperature has been studied by UV–Vis, Raman, and FTIR spectroscopic techniques. Optical properties and chemical behavior under the influence of atmospheric positive electric pulsed corona discharges were also examined. The effects of UV–Vis irradiation changed some optical parameters, such as decrease in optical density on the absorption spectrum and formation of photoproducts, due to the chromaticity removal. No significant optical changes were observed in the light absorption upon UV-irradiation but large changes in absorption spectrum were observed after positive electric corona discharge treatments, FTIR and Raman spectra in non-polar solvent are recorded and interpreted.

Oxygen-Free Conversion of Methane to Ethylene in a Plasma-Followed-by-Catalyst (PFC) Reactor

Oxygen-free conversion of methane to ethylene was investigated in a two-stage plasma-followed-by-catalyst (PFC) reactor. In the absence of catalyst, pulsed spark discharges and pulsed corona discharges were compared for methane conversion. The results showed that methane was mainly converted to acetylene, but pulsed spark discharges exhibited distinct advantages over the pulsed corona discharges in methane conversion. Thereby, pulsed spark discharges were employed and followed by Ag-Pd/SiO2 catalyst for achieving ethylene as a target product in the PFC reactor. Using the PFC reactor, a steady single-pass ethylene yield of 57% was obtained at a rate of methane conversion of 74%.

Influence of gas components on the oxidation of elemental mercury by positive pulsed corona discharge

This study examines the effect of flue gas components on the oxidation of gaseous elemental mercury (Hg0) to HgO and HgCl2 via pulsed corona discharge (PCD), where the reaction temperature was set to 90°C and the gas stream consisting of 3% H2O and 10% O2 in N2 was mixed with 45 μg m−3 Hg0, 108 ppm NO x , 80 ppm HCl, 200 ppm SO2 and 470 ppm NH3. It has been observed that O2 and HCl components in the gas stream act as oxidizing precursors through the generation of oxidizing species (O, O3, Cl and Cl2) in the PCD process. The presence of NO directly hampers Hg0 oxidation to HgO due to preferential reaction of NO with O and O3. In contrast, the presence of SO2 indirectly influences the oxidation of Hg0 to HgCl2 through the fast reaction of SO2 with OH radical, resulting in consuming OH radicals which are partially responsible for the formation of chlorine species, i.e. Cl and Cl2. It has been also found that NH3 component significantly hinders the oxidation of Hg0 to HgCl2 through the fast acid–base reaction...

High-Speed Visualization of Flame Reaction Zone Using a Positive Point-to-Plane Corona Discharge

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We have used a pulsed corona discharge to obtain time-resolved spectrally filtered 337.1-nm <formula formulatype="inline"><tex>$N_{2}(C \rightarrow B)$</tex></formula> emission images for the visualization of the reaction zone (flame front) of a premixed propane–air flame. The low-density region at the flame front allows one to guide the streamer along the reaction zone during the initial stages of the pulsed discharge, while the temperature-dependent electron-detachment/attachment rate allows for the increased conductivity of the plasma after the discharge has been fully established. Images with 500-shot accumulations are presented to clearly illustrate the concept, while the ability for greater time resolution is discussed as an attractive means for imaging small-scale turbulent instabilities in a flame reaction zone. </para>

Mach 3 Shock Wave Unsteadiness AlleviationUsing a Negative Corona Discharge

This paper reports experimental data obtained in ONERA M = 3 R1Ch blow-down wind tunnel. A truncated conical body with a central spike mounted on the truncated face is tested in a M = 3 airflow. Several runs have been performed, with a freestream unit Reynolds varying in the range Reu 2 [0.9 10 7 m 1 ; 2.1 10 7 m 1 ]. Depending on the spike length LS, the flow around the body is steady or unsteady. Following Kuo, 1 the model is also a pair of electrodes and is supplied with AC or DC power. Thus on-board discharges can be generated. Although different discharge regimes have been obtained on steady or unsteady flowfield, we simply report here the effect of corona discharges on an unsteady flowfield. This unsteadiness is characterized by a shock pulsation at the reduced frequency St = fc.LS/u0 = 3.10 2 . We observe a complete alleviation of the shock unsteadiness when a negative discharge is generated at the spike tip. With positive discharges, the effect is weaker. In both cases the input power is less than 1W. Discharge imaging and current measurements suggest that the negative discharge is a Trichel pulse corona discharge, whereas the positive discharge possibly involves streamers. The possible channels of interaction between the discharge and the airflow are briefly discussed.

Pulsed corona discharge for oxidation of gaseous elemental mercury

Positive pulsed corona discharge has been applied for the oxidation of gaseous elemental mercury (Hg0) from a simulated flue gas. The oxidation of Hg0 to HgO and HgCl2 can significantly enhance the mercury removal from flue gas. At a gas condition of O2 (10%), H2O (3%), and N2 (balance), Hg0 oxidation efficiency of 84% was achieved at an input energy density of 45J∕l. The presence of NO, however, hinders Hg0 oxidation due to the preferential reaction of NO with O and O3. On the contrary, SO2 shows little effect on Hg0 oxidation due to its preferential reaction with OH. It has been also observed that the HCl in gas stream can be dissociated to Cl and Cl2 and can induce additional Hg0 oxidation to HgCl2.

Ultraviolet radiation from the pulsed corona discharge in water

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (∼1–3 J pulse−1) was performed using the potassium ferrioxalate actinometry. Photon flux J190–280 and radiant energy Q190–280 of the UV light emitted from the discharge at spectral region 190–280 nm was determined in dependence on the applied voltage (17–29 kV, positive polarity) and the solution conductivity (100–500 µS cm−1). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders of magnitude within the range of solution conductivities 100–500 µS cm−1. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190–280 = 44.33 (quanta pulse−1). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

Modeling of the production of OH and O radicals in a positive pulsed corona discharge plasma

A mathematical model was applied to describe the behavior of OH and O radicals in positive pulsed corona discharge of N 2–H 2O mixture gas. The model takes into account the generation and disappearance of radials in a pulsed corona discharge reactor by a single pulse or continuous pulses. Their concentrations were derived by considering direct electron effect on the dissociation of gaseous molecules (O 2, N 2, H 2O) and subsequent excitation transfer reaction of excited oxygen atoms to produce OH radicals. The equations promoted could be solved numerically with the FORTRAN subroutine Treanor. So as to establish the validity of the model simulation, the calculated results were compared with the experimental data. Although there is some discrepancy between the calculation and experiment, the total trend is coincident.

Small Corona Cage for Wideband HVac Radio Noise Studies: Rationale and Critical Design

Corona cages are used in overhead power line studies to investigate physical mechanisms involved in corona discharge and to predict radio noise generation. In this paper, we design a small laboratory corona cage to investigate wideband radio noise generation on practical HVac conductor bundles. We introduce and describe cage design criteria including the insulation of the cage mesh. Our measurement method generates data that can be used to calculate the characteristics of both fair-weather and foul-weather radio noise for interference studies over a wide bandwidth. We achieve this through time-domain measurements obtained on an 8-bit, 100-MHz sampling card. Single and multiple corona pulses are studied and we propose a single corona pulse source excitation function for small cages.

Charge Assisted Laser Desorption/Ionization Mass Spectrometry of Droplets

We propose and evaluate a new mechanism to account for analyte ion signal enhancement in ultraviolet-laser desorption mass spectrometry of droplets in the presence of corona ions. Our new insights are based on timing control of corona ion production, laser desorption, and peptide ion extraction achieved by a novel pulsed corona apparatus. We demonstrate that droplet charging rather than gas-phase ion-neutral reactions is the major contributor to analyte ion generation from an electrically isolated droplet. Implications of the new mechanism, termed charge assisted laser desorption/ionization (CALDI), are discussed and contrasted with those of the laser desorption atmospheric pressure chemical ionization method (LD-APCI). It is also demonstrated that analyte ion generation in CALDI occurs with external electric fields about one order of magnitude lower than those needed for atmospheric pressure matrix assisted laser desorption/ionization or electrospray ionization of droplets.

Instrumentation for Pulsed Corona Discharge Generation Applied to Water

In this paper, we present a model (which is structured as an equivalent electric circuit whose elements are identified and deducted from the nature of the medium, the ionization and expansion process of the streamers that convey the prebreakdown current, and the energy associated to the electric breakdown in water) and a simulation of a pulsed corona discharge (PCD). Considering this, a coaxial reactor and an inexpensive and compact high-voltage pulsed-power supply (PPS) system were designed and constructed with the purpose of carrying out the PCD experimentally. The simulation results enable the prediction of the behavior of the discharge. The coaxial reactor is constituted by a cylindrical chamber and a straight central rod. The PPS operates within the 100-2000-Hz repetition rate and 0-30-kV amplitude ranges. All the system has been tested, and the first electrical results, voltage, and current waveforms, are presented.

Measurement of gas temperature and OH density in the afterglow of pulsed positive corona discharge

The gas temperature and OH density in the afterglow of pulsed positive corona discharge are measured using the laser-induced predissociation fluorescence (LIPF) of OH radicals. Discharge occurs in a 13 mm point-to-plane gap in an atmospheric-pressure H2O(2.8%)/O2(2.0%)/N2 mixture. The temperature measurement shows that (i) the temperature increases after discharge and (ii) the temperature near the anode tip (within 1 mm from the anode tip) is much higher than that of the rest of the discharge volume. Near the anode tip, the temperature increases from 500 K (t = 0 µs) to 1100 K (t = 20 µs), where t is the postdischarge time, while it increases from 400 K (t = 0 µs) to 700 K (t = 100 µs) in the rest of the discharge volume away from the anode tip. This temperature difference between the two volumes (near and far from the anode tip) causes a difference in the decay rate of OH density: OH density near the anode tip decays approximately 10 times slower than that far from the tip. The spatial distribution of OH density shows good agreement with that of the secondary streamer luminous intensity. This shows that OH radicals are mainly produced in the secondary streamer, not in the primary one.

Characteristics of atomic oxygen produced by a pulsed streamer corona discharge

Various active species can be formed by a pulsed discharge in water, and these active species may play an important role in killing bacteria and degrading organic compounds. In recent years, interest in the formation of OH, O3 and H2O2 has grown enormously. The O is also a very powerful oxidant, but little research has been done on the oxygen radical. In this paper, production of atomic oxygen by the pulsed streamer corona discharge in water has been identified. The effects of applied voltage polarity, peak voltage, oxygen and inert gases bubbling on radical formation have been investigated.

Nonthermal plasma reactors and plasma chemistry

The main goal of this paper is focused in reviewing the last 22 years of the use of nonthermal plasma reactors as alternative technologies for the treatment of residual fluid substances, regarding the destruction of hazardous compounds or the synthesis of other valuable compounds. The electrical discharge processing has emerged as alternative plasma-based technologies. Electrical discharges can be produced in different forms, depending on the geometry of the reactor and the electrical power supply. The nonthermal plasma reactors were classified into: pulsed or DC corona discharge; silent discharge or dielectric barrier discharge; surface discharge; electrified packed-bed.

Reducing Multiple Charging of Submicron Aerosols in a Corona Diffusion Charger

An existing corona diffusion charger (Buscher et al. 1994) is optimized in order to reduce multiple charging of submicron particles. A positive-zero rectangular wave voltage is applied to the inner electrode and the ion concentration in the charging region is controlled by varying the duty cycle of the pulse voltage, i.e., the fraction of time during which the voltage applied to the electrode is positive. The performance of the corona charger is assessed experimentally and theoretically for monodisperse aerosols with particle sizes in the range of 50 to 250 nm and number concentrations below 10 5 cm−3. Optimal corona voltage and pulse voltage values of +4.5 kV and +5 V are identified. A duty cycle about 10% resulted in multiple charging levels comparable to positively charged particles in bipolar chargers, with higher fractions of singly charged particles. Multiple charging can be lowered by reducing further the duty cycle. When using the corona ionizer for charging of polydisperse aerosols, operational c...

Phenomenological model of pulsed corona reactor

As it is well known, the non-thermal plasma discharge is an effective way to clean the flue and exhaust gases of hazardous pollutants, like sulphur-oxides, nitrogen-oxides. The decomposition ratio of these substances depends on the gas composition, concentration, energy distribution of fast electrons, and other parameters. For a detailed analysis of the phenomena, the first step is the mathematical description of corona pulses which determines the electric field. The second step is the determination of the electric field distribution inside the reaction chamber.In this paper the authors give an easy model for the pulsed corona current and a simplified model for the electric field by using the corona current and the displacement current pulse shapes. The result of the model is the space and time dependent field distribution, which is suitable for calculating the rate coefficients of chemical reactions.

Research on Nanosecond Pulse Corona Discharge Attenuation

A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control. Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted. The results show that the wave front decreases sharply during the corona discharge along the corona wire. The higher the amplitude of the applied pulse is, the more the amplitude of the wave front decreased. The wave attenuation responds in a lower corona discharge inversely. To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design.

Research on Nanosecond Pulse Corona Discharge with Cross Magnetic Field Applied

An application of magnetic field to the nanosecond pulse corona discharge is investigated. A cylinder reactor with different corona electrodes is set up for experimental study. A magnetic field with its direction perpendicular to the corona discharge is applied. Different discharge images are taken under single nanosecond pulse with a high sensitive UV-visible light imagine recorder. Experimental results show that with a cross magnetic field the nanosecond corona discharge both generates paths and develops homogeneously in space more than that without the magnetic field. The results may lead to a possibility to apply a cross magnetic field on nanosecond pulse corona discharge for getting higher desulfurization efficiency.