A comparative study on the spectral characteristics of nanosecond pulsed discharges in atmospheric He and a He+2.3%H_(2)O mixture

Nanosecond pulsed discharges at atmospheric pressure in a pin-to-pin electrode configuration are well reproducible in time and space, which is beneficial to the fundamentals and applications of low-temperature plasmas. In this experiment, the discharges in helium(He) and He with 2.3%water vapor(H_(2)O) are driven by a series of 10 ns overvoltage pulses(~13 k V). Special attention is paid to the spectral characteristics obtained in the center of discharges by time-resolved optical emission spectroscopy. It is found that in helium, the emission of atomic and molecular helium during the afterglow is more intense than that in the active discharge, while in the He+2.3%H_(2)O mixture, helium emission is only observed during the discharge pulse and the molecular helium emission disappears. In addition, the emissions of OH(A-X) and Hα present similar behavior that increases sharply during the falling edge of the voltage pulse as the electrons cool down rapidly. The gas temperature is set to remain low at 540 K by fitting the OH(A-X) band. A comparative study on the emission of radiative species(He, He_(2), OH and H)is performed between these two discharge cases to derive their main production mechanisms. In both cases, the dominant primary ion is He^(+) at the onset of discharges, but their He^(+) charge transfer processes are quite different. Based on these experimental data and a qualitative discussion on the discharge kinetics, with regard to the present discharge conditions, it is shown that the electron-assisted three-body recombination processes appear to be the significant sources of radiative OH and H species in high-density plasmas.

Electron characteristics and dynamics in sub-millimeter pulsed atmospheric dielectric barrier discharge

The discharge characteristics and mechanism of sub-millimeter pulsed dielectric barrier discharge in atmosphericpressure helium are investigated experimentally and theoretically, demonstrating that when the discharge gap distance is reduced from 1.00 mm to 0.20 mm, the discharge ignition time is reduced to approximately 40 ns and discharge intensity is enhanced in terms of the discharge optical emission intensity and density of the plasma species,(energetic electrons with energy above 8.40 e V). The simulated results show that as the discharge gap distance is further reduced to 0.10 mm,the number of energetic electrons decreases, which is attributable to the contraction of plasma bulk regime and reduction of electron density in the discharge bulk. Conversely, the proportion of energetic electrons to the total electrons in the discharge monotonically increases as the discharge gap distance is reduced from 1.00 mm to 0.10 mm. It is proposed that a gap distance of 0.12 mm is optimal to achieve a high concentration and proportion of energetic electrons in sub-millimeter pulsed atmosphere dielectric barrier discharge.

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.

Simultaneous oxidation of NO,SO_2 and Hg^0 from flue gas by pulsed corona discharge

A process capable of simultaneously oxidizing NO, SO2, and Hg^0 was proposed, using a nigh-voltage and short-duration positive pulsed corona discharge. By focusing on NO, SO2, and Hg^0 oxidation efficiencies, the influences of pulse peak voltage, pulse frequency, initial concentration, electrode number, residence time and water vapor addition were investigated. The results indicate that NO, SO2 and Hg^0 oxidation efficiencies depend primarily on the radicals （OH, HO2, O） and the active species （O3, H2O2, etc.） produced by the pulsed corona discharge. The NO, SO2 and Hg^0 oxidation efficiencies could be improved as pulse peak voltage, pulse frequency, electrode number and residence time increased, but they were reduced with increasing initial concentrations. By adding water vapor, the SO2 oxidation efficiency was improved remarkably, while the NO oxidation efficiency decreased slightly. In our experiments, the simultaneous NO, SO2, and Hg^0 oxidation efficiencies reached to 40%, 98%, and 55% with the initial concentrations 479 mg/m^3, 1040 mg/m^3, and 15.0 μg/m^3, respectively.

Treatment of Dye Wastewater by Using a Hybrid Gas/Liquid Pulsed Discharge Plasma Reactor

A hybrid gas/liquid pulsed discharge plasma reactor using a porous ceramic tube is proposed for dye wastewater treatment. High voltage pulsed discharge plasma was generated in the gas phase and simultaneously the plasma channel was permeated through the tiny holes of the ceramic tube into the water phase accompanied by gas bubbles. The porous ceramic tube not only separated the gas phase and liquid phase but also offered an effective plasma spreading channel. The effects of the peak pulse voltage, additive gas varieties, gas bubbling rate, solution conductivity and TiO2 addition were investigated. The results showed that this reactor was effective for dye wastewater treatment. The decoloration efficiency of Acid Orange II was enhanced with an increase in the power supplied. Under the studied conditions, 97% of Acid Orange II in aqueous solution was effectively decolored with additive oxygen gas, which was 51% higher than that with argon gas, and the increasing 02 bubbling rate also benefited the decoloration of dye wastewater. Water conductivity had a small effect on the level of decoloration. Catalysis of TiO2 could be induced by the pulsed discharge plasma and addition of TiO2 aided the decoloration of Acid Orange II.

Degradation of Dye Wastewater by ns-Pulse DBD Plasma

Two plasma reactors have been developed and used to degrade dye wastewater agents. The configuration of one plasma reactor is a comb-like extendable unit module consisting of 5 electrodes covered with a quartz tube and the other one is an array reactor which is extended from the unit module. The decomposition of wastewater by ns pulse dielectric barrier discharge （DBD） plasma have been carried out by atomizing the dyeing solutions into the reactors. During experiments, the indigo carmine has been treated as the waste agent. The measurements of UV-VIS absorption spectroscopy and the chemical oxygen demand （COD） are carried out to demonstrate the decomposition effect on the wastewater. It shows that the decoloration rate of 99% and the COD degradation rate of 65% are achieved with 15 min treatment in the unit reactor. The effect of electrical parameters on degradation has been studied in detail. Results from the array reactor indicate that it has a better degradation effect than the unit one. It can not only totally remove the chromogenic bond of the indigo carmine solution, but also effectively degrade unsaturated bonds. The decoloration rate reaches 99% after 10 min treatment, the decomposition rate of the unsaturated bond reaches 83% after 60 min treatment, and the COD degradation rate is nearly 74%.

Factors Influencing the Electron Yield of Needle-Ring Pulsed Corona Discharge Electron Source for Negative Ion Mobility Spectrometer

A simple negative ion mobility spectrometer （IMS） is designed and used to investi- gate the factors that influence the number and efficiency of electrons generated by the needle-ring pulsed corona discharge electron source. Simulation with Ansoft Maxwell 12 is carried out to analyze the electric field distribution within the IMS, and to offer the basis and foundation for analyzing the measurement results. The measurement results of the quantities of electrons show that when the drift electric field strength and the ring inner diameter rise, both the number of ef- fective electrons and the effective electron rate are increased. When the discharge voltage becomes stronger, the number of effective electrons goes up while the effective electron rate goes down. In light of the simulation results, mechanisms underlying the effects of drift electric field strength, ring inner diameter, and discharge voltage on the effective electron number and effective electron rate are discussed. These will make great sense for designing negative ion mode IMS using the needle-ring pulsed corona discharge as the electron source.

The Nonlinear Behaviors in Atmospheric Dielectric Barrier Multi Pulse Discharges

An in-depth and comprehensive understanding of the complex nonlinear behaviors in atmospheric dielectric barrier discharge is significant for the stable operation and effective control of the plasma. In this paper, we study the nonlinear behaviors in argon atmospheric dielectric barrier multi pulse discharges by a one-dimensional fluid model. Under certain conditions, the multi pulse discharge becomes very sensitive with the increase of frequency, and the multi pulse period-doubling bifurcation, inverse period-doubling bifurcation and chaos appear frequently. The discharge can reach a relatively steady state only when the discharges are symmetrical between positive and negative half cycle. In addition, the effects of the voltage on these nonlinear discharges are also studied. It is found that the amplitude of voltage has no effects on the number of discharge pulses in multi-pulse period-doubling bifurcation sequences; however, to a relatively stable periodic discharge, the discharge pulses are proportional to the amplitude of the applied voltage within a certain range.

Inactivation of Bacteria in Oil Field Injected Water by a Pulsed Plasma Discharge Process

Pulsed plasma discharge was employed to inactivate bacteria in the injection water for an oil field. The effects of water conductivity and initial concentration of bacteria on elimination efficiency were investigated in the batch and continuous flow modes. It was demonstrated that Fe2＋ contained in injection water could enhance the elimination efficiency greatly. The addition of reducing agent glutathione （GSH） indicated that active radicals generated by pulsed plasma discharges played an important role in the inactivation of bacteria. Moreover, it was found that the microbial inactivation process for both batch and continuous flow mode well fitted the model based on the Weibull＇s survival function.

Temperature field at time of pulse current discharge in metal structure with elliptical embedding crack

Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow through an elliptical embedding crack and the fluid flow through a barrier is made based on the similarity principle. Boundary conditions derived from this theory are introduced so that the distribution of current density and the temperature field expressions can be obtained. The study provides a theoretic basis to the applications of stopping spatial crack with electromagnetic heating.

Synergistic Decolouration of Azo Dye by Pulsed Streamer Discharge Immobilized TiO_2 Photocatalysis

Photocatalyst was prepared by immobilizing TiO2 on glass beads using the traditional sol-gel method. Ultraviolet light （UV） produced by pulsed streamer discharge was then used to induce photocatalytic activity of TiO2 photocatalyst. Decolouration efficiency of the representative azo dye （acid orange 7, AOT） was investigated using the synergistic system of pulsed streamer discharge plasma and TiO2 photocatalysis. The obtained results showed that the decolouration rate of AO7 could be increased by 16.7% under the condition of adding supported TiO2 in the pulsed streamer discharge system, compared to that in the sole pulsed streamer discharge plasma system, due to the synergistic effect of pulsed streamer discharge and TiO2 photocatalysis induced by pulsed streamer discharge. The synergistic system of pulsed streamer discharge and TiO2 photocatalyst was found to have more reactive radicals for degradation of organic compounds in water.

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study,a coaxial transmission line resonator is constructed,which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon,nitrogen,or even air,respectively.Although the different kinds of working gas induce the different discharge performance,their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods,and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 10^(18)m^(-3).The tail region of plasma jets all contain a large number of active particles,like NO,O,emitted photons,etc,but without O_(3).The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields,the ionization wave propulsion,and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets.The parameters of plasma jet could be modulated by adjusting microwave power,modulation pulse parameters(modulation frequency and duty ratio),gas type and its flow rate,according to the requirements of application scenarios.

A comparative study on the activity of TiO_2 in pulsed plasma under different discharge conditions

In the present study,a combination of pulsed discharge plasma and TiO2（plasma/TiO2）has been developed in order to study the activity of TiO2by varying the discharge conditions of pulsed voltage,discharge mode,air flow rate and solution conductivity.Phenol was used as the chemical probe to characterize the activity of TiO2in a pulsed discharge system.The experimental results showed that the phenol removal efficiency could be improved by about 10%by increasing the applied voltage.The phenol removal efficiency for three discharge modes in the plasma-discharge-alone system was found to be highest in the spark mode,followed by the spark–streamer mode and finally the streamer mode.In the plasma/TiO2system,the highest catalytic effect of TiO2was observed in the spark–streamer discharge mode,which may be attributed to the favorable chemical and physical effects from the spark–streamer discharge mode,such as ultraviolet light,O3,H2O2,pyrolysis,shockwaves and high-energy electrons.Meanwhile,the optimal flow rate and conductivity were 0.05 m^3l^（-1）and 10μS cm^（-1）,respectively.The main phenolic intermediates were hydroquinone,catechol,and p-benzoquinone during the discharge treatment process.A different phenol degradation pathway was observed in the plasma/TiO2system as compared to plasma alone.Analysis of the reaction intermediates demonstrated that p-benzoquinone reduction was selectively catalyzed on the TiO2surface.The effective decomposition of phenol constant（De）increased from 74.11%to 79.16%when TiO2was added,indicating that higher phenol mineralization was achieved in the plasma/TiO2system.

Electrical Characteristics of Pulsed Corona Discharge Plasmas in Chitosan Solution

Pulsed discharge plasma has exhibited active potential to prepare low molecular weight chitosan. In the present study, the viscosity of ehitosan solution was decreased noticeably after treated with pulsed corona discharge plasma. An experimental investigation on electrical characteristics of pulsed corona discharge plasma in chitosan solution was conducted with a view toward getting insight into discharge process. Factors affecting I-V curve, single pulse injec- tion energy and pulse width were studied. Experimental results showed positive effect of pulsed peak voltage on discharge plasma in chitosan solution. Pulse-forming capacitor greatly influenced the discharge form, and 4 nF was observed as a suitable value for efficiently generating stable discharge plasmas. As the electrode distance was larger than 10 ram, it had slight impact on dis- charge plasma due to the excellent conductive-property of chitosan solution. The injection energy significantly increased with air flow rate, while the pulse width hardly changed as the air flow rate increased from 0.5 m^3/h to 1.0 m^3/h. This study is expected to provide reference for promoting the application of pulsed corona discharge plasma to ehitosan solution treatment.

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.

Regeneration of Acid Orange 7 Exhausted Granular Activated Carbon Using Pulsed Discharge Plasmas

In this paper, a pulsed discharge plasma （PDP） system with a multi-needle-to-plate electrodes geometry was set up to investigate the regeneration of acid orange 7 （AO7） exhausted granular activated carbon （GAC）. Regeneration of GAC was studied under different conditions of peak pulse discharge voltage and water pH, as well as the modification effect of GAC by the pulse discharge process, to figure out the regeneration efficiency and the change of the GAC structure by the PDP treatment. The obtained results showed that there was an appropriate peak pulse voltage and an optimal initial pH value of the solution for GAC regeneration. Analyses of scanning electron microscope （SEM）, Boehm titration, Brunauer-Emmett-Teller （BET）, Horvath-Kawazoe （HK）, and X-ray Diffraction （XRD） showed that there were more mesopore and macropore in the regenerated GAC and the structure turned smoother with the increase of discharge voltage; the amount of acidic functional groups on the GAC surface increased while the amount of basic functional groups decreased after the regeneration process. From the result of the XRD analysis, there were no new substances produced on the GAC after PDP treatment.

Strengthening leaching effect of Carlin-type gold via high-voltage pulsed discharge pretreatment

A high-voltage pulsed discharge(HVPD)pretreatment was used to strengthen the leaching effect of Carlin-type gold ore containing arsenic.Optimal results of the pretreatment experiments were obtained at the following operating conditions:a spherical gap spacing of 20 mm,pulse number of 100,and voltage of 30 kV.The leaching rate of gold was increased by 15.65%via the HVPD pretreatment.The mass fraction of–0.5+0.35 mm and–0.35+0.1 mm was increased by 10.97%and 6.83%compared to the untreated samples,respectively,and the Au grade of–0.1 mm was increased by 22.84%.However,the superiority of the HVPD pretreatment would be weakened by prolonged grinding time.Scanning electron microscopy results indicated that the pretreated products presented as a melting state and then condensation,accompanying by some pore formation.More micro-cracks were generated at the interface of the ore and the original crack were expended via pulsed discharge pretreatment,with the contact area between the leaching reagent and ore increased,the leaching reaction rate enhanced and the leaching effect strengthened.

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.

Activation of peroxydisulfate by gas-liquid pulsed discharge plasma to enhance the degradation of p-nitrophenol

Pulsed discharge in water and over water surfaces generates ultraviolet radiation,local high temperature,shock waves,and chemical reactive species,including hydroxyl radicals,hydrogen peroxide,and ozone.Pulsed discharge plasma（PDP） can oxidize and mineralize pollutants very efficiently,but high energy consumption restricts its application for industrial wastewater treatment.A novel method for improving the energy efficiency of wastewater treatment by PDP was proposed,in which peroxydisulfate（PDS） was added to wastewater and PDS was activated by PDP to produce more strong oxidizing radicals,including sulfate radicals and hydroxyl radicals,leading to a higher oxidation capacity for the PDP system.The experimental results show that the increase in solution conductivity slightly decreased the discharge power of the pulse discharge over the water surface.An increase in the discharge intensity improved the activation of PDS and therefore the degradation efficiency and energy efficiency of p-nitrophenol（PNP）.An increase in the addition dosage of PDS greatly facilitated the degradation of PNP at a molar ratio of PDS to PNP of lower than 80：1,but the performance enhancement was no longer obvious at a dosage of more than 80：1.Under an applied voltage of 20 kV and a gas discharge gap of 2 mm,the degradation efficiency and energy efficiency of the PNP reached 90.7%and45.0 mg kWh^（-1） for the plasma/PDS system,respectively,which was 34%and 18.0 mg kWh^（-1）higher than for the discharge plasma treatment alone.Analysis of the physical and chemical effects indicated that ozone and hydrogen peroxide were important for PNP degradation and UV irradiation and heat from the discharge plasma might be the main physical effects for the activation of PDS.

A novel technology of high-voltage pulse discharge for comminution of galena ore

An innovative technology of high-voltage pulse discharge(HVPD)was proposed to investigate the comminution characteristics of galena ore.The optimal experiment parameters were determined as follows:spark gap spacing of 25 mm,pulse number of 120,and voltage of 25 k V.The mass fraction with size<0.074 mm in ground products was improved by the HVPD.Meanwhile,the relative grindability declined with the increase of the grinding time,which indicated that the superiority of HVPD was weakened.The ground products of HVPD were distributed more homogeneously than those of mechanical crushing.The liberation of breakage products was improved by 24.57%via the HVPD.Moreover,the Brunauer–Emmett–Teller(BET)specific surface area,pore volume,and average pore size were increased via the HVPD.Scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS)analyses suggested that obvious grain-boundary breakage and several stomatal traces were observed in the HVPD products.