Experimental study on the effect of H_(2)O and O_(2) on the degradation of SF_(6) by pulsed dielectric barrier discharge

SF_(6) has excellent insulation performance and arc extinguishing ability,and is widely used in the power industry.However,its global warming potential is about 23,500 times that of C0_(2),it can exist stably in the atmosphere,it is not easily degradable and is of great potential harm to the environment.Based on pulsed dielectric barrier discharge plasma technology,the effects of H_(2)O and 0_(2) on the degradation of SF_(6) were studied.Studies have shown that H_(2)O can effectively promote the decomposition of SF_(6) and improve its degradation rate and energy efficiency of degradation.Under the action of a pulse input voltage and input frequency of 15 kV and 15 kHz,respectively,when H_(2)O is added alone the effect of 1% H_(2)O is the best,and the rate and energy efficiency of degradation of SF_(6) reach their maximum values,which are 91.9% and 8.25 g kWh^(-1),respectively.The synergistic effect of H_(2)O and O_(2) on the degradation of SF_(6) was similar to that of H_(2)O.When the concentration of H_(2)O and O_(2) was 1%,the system obtained the best rate and energy efficiency of degradation,namely 89.7% and 8.05 g kWh~(-1),respectively.At the same time,different external gases exhibit different capabilities to regulate decomposition products.The addition of H_(2)O can effectively improve the selectivity of S0_(2).Under the synergistic effect of H_(2)O and O_(2),with increase in O_(2) concentration the degradation products gradually transformed into SO_(2)F_(2).From the perspective of harmless treatment of the degradation products of SF_(6),the addition of O_(2) during the SF_(6) degradation process should be avoided.

Experimental and numerical investigation on the uniformity of nanosecond pulsed dielectric barrier discharge influenced by pulse parameters

Nanosecond(ns)pulsed dielectric barrier discharge(DBD)is considered as a promising method to produce controllable large-volume and high activity low-temperature plasma at atmospheric pressure,which makes it suitable for wide applications.In this work,the ns pulse power supply is used to excite Ar DBD and the influences of the pulse parameters(voltage amplitude,pulse width,pulse rise and fall times)on the DBD uniformity are investigated.The gas gap voltage(Ug)and conduct current(Ig)are separated from the measured voltage and current waveforms to analyze the influence of electrical parameters.The spectral line intensity ratio of two Ar excited species is used as an indicator of the electron temperature(Te).The time resolved discharge processes are recorded by an intensified charge-coupled device camera and a one-dimensional fluid model is employed to simulate the spatial and temporal distributions of electrons,ions,metastable argon atoms and Te.Combining the experimental and numerical results,the mechanism of the pulse parameters influencing on the discharge uniformity is discussed.It is shown that the space electric field intensity and the space particles'densities are mainly responsible for the variation of discharge uniformity.With the increase of voltage and pulse width,the electric field intensity and the density of space particles increased,which results in the discharge mode transition from non-uniform to uniform,and then non-uniform.Furthermore,the extension of pulse rise and fall times leads to the discharge transition from uniform to nonuniform.The results are helpful to reveal the mechanism of ns pulsed DBD mode transition and to realize controllable and uniform plasma sources at atmospheric pressure.

Nanosecond Repetitively Pulsed Dielectric Barrier Discharge in Air at Atmospheric Pressure

Dielectric barrier discharge （DBD） between two cylindrical glass containers with salt water generated by a nanosecond repetitively pulsed power generator is reported. The electrical parameters, luminous images and spectrum diagnosis are presented. It is shown that the DBD possesses a large discharge current and an intense optical emission from the nitrogen second positive system below 400 nm. The gas temperature remains very close to room temperature regardless of pulse polarity. Luminous photographs with a short exposure time down to 2 ns indicate that no filament is observed and the discharge is homogeneous.

Effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge in atmospheric airflow

In this paper,an asymmetric electrode geometry(the misalignment between the ends of highvoltage and grounded electrodes)is proposed in order to investigate the effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge(DBD).The results show that diffuse discharge manifests in the misaligned region and the micro-discharge channel in the aligned region moves directionally.Moreover,the diffuse discharge area increases with the decrease of the discharge gap and pulse repetition frequency,which is consistent with the variation of the moving velocity of the micro-discharge channel.When airflow is introduced into the discharge gap in the same direction as the transverse electric field,the dense filamentary discharge region at the airflow inlet of asymmetric electrode geometry is larger than that of symmetric electrode geometry.However,when the direction of the airflow is opposite to that of the transverse electric field,the dense filamentary discharge region of asymmetric electrode geometry is reduced.The above phenomena are mainly attributed to the redistribution of the space charges induced by the transverse electric field.

Effects of Oxygen Concentration on Pulsed Dielectric Barrier Discharge in Helium-Oxygen Mixture at Atmospheric Pressure

In this work the effects of O_2 concentration on the pulsed dielectric barrier discharge in helium-oxygen mixture at atmospheric pressure have been numerically researched by using a one-dimensional fluid model in conjunction with the chosen key species and chemical reactions.The reliability of the used model has been examined by comparing the calculated discharge current with the reported experiments. The present work presents the following significant results. The dominative positive and negative particles are He_2~＋ and O_2^-, respectively, the densities of the reactive oxygen species（ROS） get their maxima nearly at the central position of the gap, and the density of the ground state O is highest in the ROS. The increase of O_2 concentration results in increasingly weak discharge and the time lag of the ignition. For O_2 concentrations below 1.1%,the density of O is much higher than other species, the averaged dissipated power density presents an evident increase for small O_2 concentration and then the increase becomes weak. In particular,the total density of the reactive oxygen species reaches its maximums at the O_2 concentration of about 0.5%. This characteristic further convinces the experimental observation that the O_2 concentration of 0.5% is an optimal O_2/He ratio in the inactivation of bacteria and biomolecules when radiated by using the plasmas produced in a helium oxygen mixture.

The Experimental Investigations of Dielectric Barrier Discharge and Pulse Corona Discharge in Air Cleaning

The dielectric barrier discharge (DBD) and pulse corona discharge(PCD) plasma generator was used to remove NH3, H2S, C7H8 etc. from atmosphere. The principle and characteristic of the two ways was discussed in the article. The test shows the result of PCD is better than that of DBD.

Numerical investigation on the effect of gas parameters on ozone generation in pulsed dielectric barrier discharge

Pulsed dielectric barrier discharge is a promising technology for ozone generation and is drawing increasing interest. To overcome the drawback of experimental investigation, a kinetic model is applied to numerically investigate the effect of gas parameters including inlet gas temperature, gas pressure, and gas flow rate on ozone generation using pulsed dielectric barrier discharge. The results show that ozone concentration and ozone yield increase with decreasing inlet gas temperature, gas pressure, and gas flow rate. The highest ozone concentration and ozone yield in oxygen are about 1.8 and 2.5 times higher than those in air, respectively. A very interesting phenomenon is observed： the peak ozone yield occurs at a lower ozone concentration when the inlet gas temperature and gas pressure are higher because of the increasing average gas temperature in the discharge gap as well as the decreasing reduced electric field and electron density in the microdischarge channel. Furthermore, the sensitivity and rate of production analysis based on the specific input energy （SIE） for the four most important species 03, O, O（1D）, and O2（b1∑） are executed to quantitatively understand the effects of every reaction on them, and to determine the contribution of individual reactions to their net production or destruction rates. A reasonable increase in SIE is beneficial to ozone generation. However, excessively high S1E is not favorable for ozone production.

Particle Densities of the Atmospheric-Pressure Argon Plasmas Generated by the Pulsed Dielectric Barrier Discharges

Atmospheric-pressure argon plasmas have received increasing attention due to their high potential in many industrial and biomedical applications. In this paper, a 1-D fluid model is used for studying the particle density characteristics of the argon plasmas generated by the pulsed dielectric barrier discharges. The temporal evolutions of the axial particle density distributions are illustrated, and the influences of changing the main discharge conditions on the averaged particle densities are researched by independently varying the various discharge conditions. The calculation results show that the electron density and the ion density reach two peaks near the momentary cathodes during the rising and the falling edges of the pulsed voltage. Compared with the charged particle densities, the densities of the resonance state atom Arr and the metastable state atom Arm have more uniform axial distributions, reach higher maximums and decay more slowly. During the platform of the pulsed voltage and the time interval between the pulses, the densities of the excited state atom Ar＊ are far lower than those of the Arr or the Arm. The averaged particle densities of the different considered particles increase with the increases of the amplitude and the frequency of the pulsed voltage. Narrowing the discharge gap and increasing the relative dielectric constant of the dielectric also contribute to the increase of the averaged particle densities. The effects of reducing the discharge gap distance on the neutral particle densities are more significant than the influences on the charged particle densities.

Multiple current peaks and spatial characteristics of atmospheric helium dielectric barrier discharges with repetitive unipolar narrow pulse excitation

Atmospheric dielectric barrier discharges driven by repetitive unipolar narrow pulse excitation are investigated numerically by using one-dimensional fluid models.The one-dimensional simulation focuses on the effects of applied voltage amplitude,pulse repetition frequency,gap width andγcoefficient on the multiple-current-pulse(MCP)discharge.The results indicate that the MCP behavior will lead to the stratification of electron density distribution in axial direction.Traditional MCP manipulating methods,such as reducing the applied voltage amplitude,increasing the applied voltage frequency,adjusting the gap width,cannot regulate MCPs exhibiting in this work.Further analyses reveal that the increasing electric field of the cathode fall region is the basis for the emergence of MCP behavior.

Research on the characteristics of atmospheric air dielectric barrier discharge under different square wave pulse polarities

Energy efficiency limits the application of atmospheric pressure dielectric barrier discharge(DBD),such as air purification,water treatment and material surface modification.This article focuses on the electrical and optical effects of the DBD under three square wave pulses polarities-positive,negative and bipolar.The result shows that under the same voltage with the quartz glass medium,the discharge efficiency of bipolar polarity pulse is the highest due to the influence of deposited charge.With the increase of air gap distance from 0.5 to 1.5 mm,average power consumed by the discharge air gap and discharge efficiency decrease obviously under alumina,and increase,and then decrease under quartz glass and polymethyl methacrylate(PMMA).Through spectrum diagnosis,in the quartz glass medium,the vibration temperature is the highest under negative polarity pulse excitation.Under bipolar pulse,the vibration temperature does not change significantly with the change of air gap distance.For the three dielectric materials of quartz glass,alumina and PMMA,the molecular vibration temperature is the highest under the quartz glass medium with the same voltage.When the gap spacing,pulse polarity or dielectric material are changed,the rotational temperature does not change significantly.

Sterilization mechanism of helium/helium-oxygen atmospheric-pressure pulsed dielectric barrier discharge on membrane surface

Pulsed dielectric barrier discharge(PDBD) exhibits several applications in different fields;however,the interaction of its components with substances remains a key issue.In this study,we employed experimental and numerical modeling to investigate the interactions between different PDBD components and substances in pure helium and a helium-oxygen mixture.A membrane comprising a Staphylococcus aureus strain was utilized as the treatment object to demonstrate the trace actions of the evolutions and distributions of certain components on the surface of the substance.The results revealed that the shapes and sizes of the discharging area and inhibition zone differed between groups.Under a pure helium condition,a discharge layer existed along the membrane surface,lying beside the main discharging channel within the electrode area.Further,an annulus inhibition zone was formed at the outer edge of the electrode in the pure helium group at 30 s and 1 min,and this zone extended to a solid circle at 2 min with a radius that was~50% larger than that of the electrode radius.Nevertheless,the discharging channel and inhibition zone in the helium-oxygen mixture were constrained inside the electrode area without forming any annulus.A 2D symmetrical model was developed with COMSOL to simulate the spatiotemporal distributions of different particles over the membrane surface,and the result demonstrated that the main components,which formed the annulus inhibition zone under the pure helium condition,contributed to the high concentration of the He^(+)annulus that was formed at the outer edge of the electrode.Moreover,O^(+)and O_(2)^(+)were the main components that killed the bacteria under the helium-oxygen mixture conditions.These results reveal that the homogenization treatment on a material surface via PDBD is closely related to the treatment time and working gas.

Numerical Study of Pulsed Dielectric Barrier Discharge at Atmospheric Pressure Under the Needle-Plate Electrode Configuration

In this paper, we study the characteristics of atmospheric-pressure pulsed dielectric barrier discharge （DBD） under the needle-plate electrode configuration using a one-dimensional self-consistent fluid model. The results show that, the DBDs driven by positive pulse, negative pulse and bipolar pulse possess different behaviors. Moreover, the two discharges appearing at the rising and the falling phases of per voltage pulse also have different discharge regimes. For the case of the positive pulse, the breakdown field is much lower than that of the negative pulse, and its propagation characteristic is different from the negative pulse DBD. When the DBD is driven by a bipolar pulse voltage, there exists the interaction between the positive and negative pulses, resulting in the decrease of the breakdown field of the negative pulse DBD and causing the change of the discharge behaviors. In addition, the effects of the discharge parameters on the behaviors of pulsed DBD in the needle-plate electrode configuration are also studied.

Degradation of phenol using a combination of granular activated carbon adsorption and bipolar pulse dielectric barrier discharge plasma regeneration

A combined method of granular activated carbon（GAC） adsorption and bipolar pulse dielectric barrier discharge（DBD） plasma regeneration was employed to degrade phenol in water.After being saturated with phenol,the GAC was filled into the DBD reactor driven by bipolar pulse power for regeneration under various operating parameters.The results showed that different peak voltages,air flow rates,and GAC content can affect phenol decomposition and its major degradation intermediates,such as catechol,hydroquinone,and benzoquinone.The higher voltage and air support were conducive to the removal of phenol,and the proper water moisture of the GAC was 20%.The amount of H2 O2 on the GAC was quantitatively determined,and its laws of production were similar to phenol elimination.Under the optimized conditions,the elimination of phenol on the GAC was confirmed by Fourier transform infrared spectroscopy,and the total removal of organic carbons achieved 50.4%.Also,a possible degradation mechanism was proposed based on the HPLC analysis.Meanwhile,the regeneration efficiency of the GAC was improved with the discharge treatment time,which attained 88.5% after 100 min of DBD processing.

Simulation Study on Multi-Pulse Phenomena of Atmospheric Pressure Argon Dielectric Barrier Discharge

In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge （DBD） under atmospheric pressure. The finiteelement method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.

Effect of Duty Cycle on the Characteristics of Pulse-Modulhted Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge

Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge （V-SBD） excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge （d = 0 mm） and volume added surface barrier discharges （d = 2 mm and 3 mm）. The optical emission spectra are recorded for calculating emission intensities of N2 （C3 ∏u → B3∏g） and N2＋ （B2 ∑u＋ → X2 ∑g＋）, and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d = 0 mm structure can excite the largest emission intensity of N2 （C3 ∏u → B3 ∏g）, while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of N2 ＋ （B2 ∑u＋ → X2 ∑＋g）/N2 （C3 ∏u → B3 ∏g） during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d = 3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N2 （C3 ∏u→ B3∏g） than that of d = 2 mm structure. The structure of d = 2 mm can maintain more increasing factor than that of the d = 3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.

Investigation on discharge characteristics of a coaxial dielectric barrier discharge reactor driven by AC and ns power sources

A coaxial dielectric barrier discharge（DBD） reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond（ns）pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.

Analysis of flow separation control using nanosecond-pulse discharge plasma actuators on a flying wing

Dielectric barrier discharge （DBD） plasma is one of most promising flow control method for its several advantages. The present work investigates the control authority of nanosecond pulse DBD plasma actuators on a flying wing model＇s aerodynamic characteristics. The aerodynamic forces and moments are studied by means of experiment and numerical simulation. The numerical simulation results are in good agreement with experiment results. Both results indicate that the NS-DBD plasma actuators have negligible effect on aerodynamic forces and moment at the angles of attack smaller than 16-. However, significant changes can be achieved with actuation when the model＇s angle of attack is larger than 16° where the flow separation occurs. The spatial flow field structure results from numerical simulation suggest that the volumetric heat produced by NS-DBD plasma actuator changes the local temperature and density and induces several vortex structures, which strengthen the mixing of the shear layer with the main flow and delay separation or even reattach the separated flow.

Transition of Streamer, Corona and Glow Discharges in Needle-to-plane Dielectric Barrier Discharge at Atmospheric Pressure Air

To discuss the modes of dielectric barrier discharge(DBD) between needle-to-plane electrodes in air,DBD is generated and observed on a needle-to-plane device at atmospheric pressure air.Fast images of the DBD are taken by using a charge couple device(CCD) cinema with a macro lens,while the electrical and photo-electricity waveforms of the DBD are recorded.The current waveforms show that under an applied voltage of 3 kV,there are numerous short current pulses in both positive and negative half-periods of discharges.However,under 6 kV,there are still the numerous short current pulses in the positive half-periods,but only one wide current pulse in each negative half-period.This difference is also found in the photoelectric signals.The streamer,corona and glow discharges are observed from the images of the discharges at different applied voltages.The structure of glow discharge in the negative period is exactly the same as that of the low pressure glow discharge.However,in the positive period of discharge there is always a streamer.In the negative period of discharge,while the applied voltage increases,the transition from corona to glow discharge is observed.The progress of a transition between streamer and glow discharge at 6 kV during one period is analyzed.The glow discharge appearance is determined by two factors: the discharge current is limited to a certain extent by the dielectric layer; the charges deposited on the dielectric layer during the last half period enhance the intensity of the electric field.At an insufficient applied voltage,the cathode drop leads to no glow discharge,but Trichel pulses.

Filament Discharge Phenomena in Fingerprint Acquisition by Dielectric Barrier Discharge

In this paper, the dielectric barrier discharge fingerprint acquisition technique is introduced. The filament discharge phenomena were observed in the process of fingerprint acquisition. The filament discharge reduced the quality of fingerprint images. Obviously, it was necessary to eliminate streamer discharges in order to get good fingerprint images. The streamer discharge was considered to be the cause of the filament discharge in the experiment. The relationship between the critical electric field and the discharge gap was calculated with the Raether＇s model of streamer discharge. The calculated results and our experiment proved that it would be difficult for the streamer discharge to occur when the discharge gap was narrow. With a narrow discharge gap, the discharge was homogeneous, and the fingerprint images were clear and large in area. The images obtained in the experiment are very suitable for fingerprint identification as they contain more information.