Efficient degradation of high concentration sulfur hexafluoride by Ni doped ceria combined with dielectric barrier discharge

In the present study, the total oxidation of n-butanol and carbon monoxide (CO) was investigated on 1 wt% Pd/(-Al2O3 catalysts which were prepared via the dielectric-barrier discharge (DBD) and wet-impregnation (WI) methods. All catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller method (BET). The catalytic activities in the total oxidation of VOCs (n-butanol) and CO under gas-phase conditions was measured. The results showed that the palladium catalysts prepared from DBD method exhibited higher activity in total oxidation of n-butanol and CO than catalysts prepared by WI method. This difference is due to better physicochemical properties of catalysts prepared by DBD method. For 1 wt% Pd loading, total oxidation of n-butanol and CO was achieved at 300 C and 175 C with the DBD method. Meanwhile, oxidation efficiency of the catalysts prepared by WI method is only approximately 90 % in two cases.

In order to study the influence of the magnetic field on the surface activity of the low-temperature anode bonding material in the dielectric barrier discharge, a dielectric barrier discharge device with and without a magnetic field is used, and the glass in the anode bonding is used as a dielectric barrier material. The results of analysis and characterization using angular contact instrument and surface free energy measuring instrument show that the dielectric angle barrier discharge plasma treatment with and without magnetic field can reduce the contact angle and free energy of the silicon/glass surface. Under the discharge gap of 0.08mm, when the magnetic field is absent, the hydrophilic angle of the glass approaches 0°, and the hydrophilic angle of the silicon wafer is as low as 19°. When the magnetic field is applied, the hydrophilic angle of the glass approaches 0°. The minimum hydrophilic angle of the tablet is up to 14°. By contrast, the hydrophilic angle and free energy of silicon/glass materials treated by a dielectric barrier discharge with magnetic field are better.

A dielectric barrier or silent discharge is the name given to a transient gas discharge occurring between two electrodes separated by one or two layers of dielectric material. They have formed the basis of commercial ozonisers for nearly a century but, despite the maturity of this technology, significant experimental and theoretical questions remain to be answered about the operation of these discharges before they can be fully exploited in new applications. Of particular interest is the potential that dielectric barrier discharges display for development as sources of intense, monochromatic, incoherent UV/VUV radiation. This paper briefly outlines the current status of the field with regard to research into the operation and UV/VUV radiative spectroscopy of dielectric barrier discharges. Some applications of these sources are briefly discussed and some of the theoretical models proposed to explain their operation are outlined. The paper concludes with a summary and outlook of the experimental and theoretical project that is being set up under a collaborative venture by CQU and ANU to study dielectric barrier discharges.

Effect of different catalysts on mesotrione degradation in water falling film DBD reactor

The paper deals with flight tests of dielectric barrier discharge control devices. Plasma activators were installed on sailplane’s wing and attempts to use them for control of flow separation in pre- and post- stall flight regimes were performed. Main efforts in this study were done to design plasma flow control system and develop flight test procedures. It was experimentally shown that plasma actuators can be used onboard of an aircraft as a part of control system. I. Introduction XISTING methods of flight safety improvement for near-stall flight regimes are developed in two directions: installation of stall warning devices and maintenance of controllability in post-critical regimes by means of vortex generators, automatic slats and other similar devices. Generally, the combination of these methods is applied, and each of them has its own lacks. Decrease of angle of attack after triggering of stall warning demands reasonable time and speed reserve. It could not be possible near the ground or in strong turbulence. Installation of vortex generators and other mechanical devices leads to additional drag, design complication and aircraft weight growth. Among modern adaptive methods of flow separation control, such as: blow-suction of boundary layer, synthetic jets and micro-mechanical activators, application of devices based on principle of the Dielectric Barrier Discharge (DBD) has doubtless advantages. These devices have simple design, insignificant weight and do not distort geometry of wing airfoil. The principle of DBD operation is based on additional acceleration and excitation of preseparated boundary layer by EHD force that consequently promotes delay of boundary layer separation up to higher angles of attack and changes its character. In real flight conditions it should also lead to reduction of stall speed of aircraft and to maintenance of controllability on post-stall angles of attack. Study of DBD application for separation control on wing airfoils have begun rather recently [1,2,3], but doubtless growing interest to the given subjects is observed by present time. The majority of the experimental studies executed by present time have been performed at low free stream speeds (up to 10 m/s) or with small airfoil models. Therefore, the questions of scaling and possibility of practical application of DBD devices for flow separation and stall control in real flight conditions remain opened. The team of Institute of Theoretical and Applied Mechanics have experience of application of DBD and other plasma discharges for flow separation control [4,5,6]. Recent experiments in wind tunnel Т-324 made with 1m span models of straight and swept wings have testified that the method is ready for approbation in real flight condition experiments. The transfer of such new technology as DBD control system from wind tunnel environment to a real aircraft is complex problem and flight experiments have to answer several important questions about practical realization and possibilities of DBD for flight control. First of all we have to try to develop high-voltage generator / plasma actuator system which is suitable for installation onboard of an aircraft from point of view of weight, power and efficiency. If such system would be designed it has to be safe in operation or special procedures have to be implemented. DBD control systems deal with RF plasma sources of significant power so practical questions such as radio-electronic emission, electrical safety and reliability of system have to be studied. The perspective goal of the project is application of DBD for maintenance of controllability of the aircraft in post-stall range of angles of attack. The purpose of current flight tests is to investigate all practical sides of DBD application mentioned above as well as to study DBD effect on flow separation on the wing in near-stall envelope of the angles of attack.

The use of plasmas in aerodynamics has become a recent topic of interest. The potentialities of different types of plasmas are being investigated for low velocity and high velocity flow control, as well as for plasma-assisted combustion. Dielectric barrier discharges (DBDs) are good candidates since the transition of the glow or filamentary discharge to an arc is prevented by the dielectric barrier. Moreover, surface DBDs allow to ionize the gas very close to the dielectric surface and can be used to ionize the boundary layer around an object immersed in a flow. The research in flow control has basically followed two main paths: the study of DBDs in low-speed airflows and the study of volume glow or corona discharges in supersonic airflows. Until today, there has been an important technological barrier in experimental investigations with surface DBDs. Atmospheric pressure surface DBDs in air have been difficult to maintain for long operation times, typically several hours, because reactive species created in the plasma (for example atomic oxygen) generate intensive etching of the electrode and dielectric materials. Oxidation of the electrodes or reduction of the dielectric thickness will eventually lead to plasma extinction or arcing respectively. This important issue has prevented detailed studies of DBDs in extreme environment, namely in high-speed airflows. In the present work, a solution to this technological problem has been found and is presented. Low temperature co-fireable ceramic (LTCC) technology allows, for the first time, to fully encapsulate the electrodes in a ceramic matrix and maximize the lifetime of the DBD system. Encapsulation improves the reproducibility of the experiments. Moreover, the plate can be manufactured in a curved shape. This technological advance permits, in the frame of the research presented here, to carry out a detailed experimental investigation of DBDs in high-speed flows. The goal of this experimental research is to improve the physical understanding of the interaction between a local atmospheric discharge, causing a localized weak ionization of the surrounding airflow, and the shock wave structure in transonic and supersonic flows typical for aeronautic applications. The fundamental nature of the research makes it relevant in a large domain of applications such as sonic boom alleviation, the reduction of aerodynamic losses (drag reduction) or combustion improvement. The surface dielectric barrier discharge is first characterized without airflow in order to understand the influence of the applied electrical conditions and the structure of the DBD plate on the discharge regime its spatial distribution. Current curves and photomultiplier measurements show that the DBD comprises a filamentary and a continuous (glow- or corona-like) component. Increasing the applied voltage ramp (dU2/dt) results in an increase in the filament generation rate and current peak amplitude. The geometry of the electrodes has little effect on the burning voltage but plays a role in the filament generation rate. Encapsulation reduces the rate of filament production and the expansion of the plasma around the upper electrode but it generates a more uniform distribution of the plasma on the surface and as a function of time. The behavior of the surface DBD in a high-speed air flow is first studied in a simple aerodynamic configuration: a flat DBD plate mounted on one wall of the nozzle. It is demonstrated that the DBD generated by this system can be sustained in supersonic airflows up to free stream Mach numbers of M∞=1.1. Current and time-resolved light emission measurements (photomultiplier) show that there are modifications in the discharge regime at high airflow velocity. For overall discharge, the filamentary to continuous component ratio is increased with increasing flow velocities, the plasma becomes relatively more filamentary. For individual microdischarges, the light pulse emission duration is reduced by one order of magnitude. These measurements indicate that there is a change in the breakdown mechanism and it is proposed that a transition from Townsend breakdown to streamer breakdown occurs when the airflow velocity is increased. The inverse problem is then addressed, the effects of the DBD on the airflow, in a case where the plasma is generated on the surface of an airfoil and interacts with the shock structure in the transonic flow field around that airfoil. Although no significant effects of the surface DBD on the normal shock generated in the transonic flow have been observed with the Schlieren visualizations and far-field pressure measurements, the flow modifies the plasma characteristics in a very significant way. In addition to the effects of the flow velocity (as observed in the flat plate experiment), the significant variation of pressure on the surface of the airfoil plays an important role. Decreasing pressure increases the number of filaments and favors high current peak generation. It shows that the discharge characteristics cannot be completely controlled and that they depend on the flow field.

Summary form only given. High-pressure, non-thermal, non-equilibrium plasma sources based on dielectric barrier discharges (DBDs) are increasingly being used in various novel applications1 but the underlying discharge mechanism is not very clear. We have developed three types of DBD cells. In this work, the xenon, argon and helium gas filled coaxial DBD cells have been studied at different working conditions. In the DBDs the in-situ diagnostics are not possible due to the small geometries and hence electrical modeling and simulation of DBDs became important to get the characteristics of discharge parameters which are not measurable during experiments such as discharge gas voltage, dielectric barrier voltage, memory charge, discharge current and discharge impedance etc. Recently we have made some efforts to understand the discharge phenomenon in the DBDs based on an equivalent electrical circuit model2, which enables electrical characterization of DBDs. Analysis is carried out in order to obtain the internal discharge parameters including variable discharge impedance which is not measurable during the experimentation processes. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance, has also been reported3 that has been further investigated. The relative intensity analysis of the Xe continuum peak at wavelength 172 nm in the optical emission spectra of VUV region is also carried out. Approximately three times increment in radiation is observed in pulse excitation than those of sinusoidal excitation which infer pulsed excitation of DBD sources are advantageous for excimer light sources.

Active flow separation control using dielectric barrier discharge (DBD) plasma actuators oriented in the spanwise direction has been successfully investigated by the authors using an integrated numerical simulation tool that couples the unsteady Reynolds averaged Navier-Stokes (URANS) or large eddy simulation (LES) solver for incompressible flows with the DBD electro-hydrodynamic (EHD) body force model. Although many experimental and numerical investigations have indicated that the spanwise-oriented DBD plasma actuator is an effective flow control method, the application is difficult to extend from model-scale to full-scale problems, partly due to the required high amplitude and high bandwidth excitation. Also, the flow control mechanism associated with a spanwise-oriented DBD actuator is mainly direct momentum injection, therefore, the effectiveness of actuation is sensitive to the location of the DBD actuator relative to the location of flow separation. On the other hand, a few experimental studies have shown promising results using the DBD Vortex Generator (DBD-VG) consisting of multiple plasma DBD actuators oriented in the streamwise direction. By generating streamwise vortices extending a long distance downstream, the DBD-VGs enhance the mixing of the inner and outer layers of turbulent boundary layer flows. As a result, the boundary layer can better withstand an adverse pressure gradient. When applied to flow separation control, the effectiveness of the DBD-VGs should be less sensitive to location of flow separation. The present work extends the capability of the integrated numerical simulation tool from a single spanwise-oriented DBD plasma actuator to multiple DBD plasma actuators oriented in any direction, including the streamwise direction. As a demonstration of the new capability in the DBD-URANS coupled solver, numerical simulations of flow induced by a DBD-VG actuator with an array of exposed electrodes in a quiescent environment, as well as in a turbulent boundary layer over a flat plate, are carried out. The numerical simulation successfully reproduced the longitudinal vortices embedded in the boundary layer.

Electrical modelling is a very important method for studying the dielectric barrier discharge (DBD). The traditional models usually simulate the dynamical behaviors of DBD through combination of many circuit elements1 and have obtained more and more accurate results as the number of parameters increases. However the increasing parameters severely increase the complexity of the models, and as a result it is difficult to flexibly describe the dynamics of the DBD according to the actual operating situation with these models. In addition, the traditional models can not reflect the inherent mechanism of the DBD. Memristor, which is a nonlinear circuit element with both resistive and memory properties and is known as the fourth fundamental circuit element, has shown many characteristics similar to the DBD, such as the parallel hysteresis phenomenon2 and the application of one-dimensional fluid model in their physical models3. The similarities between the DBD and the memristor intrigue us to wonder whether the DBD is a memristor in nature. If this assumption is true, the electrical simulation circuit could be greatly simplified and its applications would also be pushed forward tremendously. Moreover, this theory would greatly promote studies on the mechanism of the DBD. In this paper, we demonstrate that the DBD has fingerprint characteristics of the memristor through simulations using a one-dimensional fluid model, preliminarily showing the memristive nature of the DBD.

Since the last decade, the atmospheric pressure glow discharge (APGD) and dielectric barrier discharge (DBD) has utilized for numerous applications. An experimental setup is constructed for generating the APGD or DBD. When inserting a mesh wire between the electrode and barrier, APGD can be generated as the form of DBD. The discharge mechanisms of APGD and DBD are discussed, and their characteristics are investigated and compared by measuring the electrical parameters and optical emission. The APGD and DBD are also employed to modify the surface of insulating materials. The material, the thickness of dielectric barriers and the style of the mesh wires have great influences on the discharge characteristics. While the gap distance is 1/spl sim/2 mm, using the polyester or polytetrafluorethylene (PTFE) with the thickness from 0.08 mm to 0.1 mm and 325# mesh wires, it seems easy to generate homogeneous and stable APGD. The effects of APGD and DBD on the surface of PTFE are studied by the contact angle of water.

Ignition of hydrogen (H2) and hydrocarbon fuel such as ethylene (C2H4) in a supersonic flow by simultaneous operations of a dielectric barrier discharge (DBD) device and a plasma jet (PJ) torch were experimentally investigated. The DBD device generated non-equilibrium plasma while the PJ torch injected equilibrium plasma. They were in tandem arrangement installed on the bottom wall of the combustor. The main stream Mach number was 2.0, and the stagnation pressure and temperature were those of the atmospheric condition. Nitrogen was employed as feedstock gas of the PJ torch. Fuel was injected perpendicularly into the mainstream at the sonic speed from upstream of DBD device. The DBD device was discharged for generating of non-equilibrium plasma directly in the mainstream. The wall pressure on the top wall was measured for judgment of the success of ignition. For hydrogen fuel, it was clearly shown that simultaneous operation of PJ and DBD resulted in larger wall pressure increase than that without the DBD operation. Ignition and combustion of ethylene fuel occurred by the PJ with higher input power comparing with one required for hydrogen fuel. However, there was no clear difference in the wall pressure distributions by adding the DBD operation. The effect of ignition and combustion enhancement of ozone, which might be produced by the DBD operation, was numerical simulated in regard to hydrogen and ethylene. The ozone accelerates ignition reaction of a hydrogen/air and ethylene/air mixture as almost the same as O, H and N radicals. Even if the mole fraction of active species such as ozone was increased, the ignition delay time of ethylene was longer than hydrogen of it.

The discharge mode and photoelectric characteristics of Ar/NH3 DBD (dielectric barrier discharge) are studied to discuss the stability of the discharge under the influence of Penning ionization and attachment reaction. There are three discharge modes, including stable uniform glow discharge, unstable glow discharge and unstable columnar discharge. Discharge instability, including nonuniform discharge and discharge channel split, occurs under low (<0.10%) or high (>0.35%) volume fractions of NH3, which are understood to be caused by an insufficiently strong Penning effect or a strong attachment reaction, respectively. The attachment reaction of NH3 can also lead to a weaker emission intensity for Ar/NH3 DBD, in particular regarding the emission of OH(A2Σ+). Ar/NH3 and He/N2 DBDs are also compared. In He/N2 DBD, the emission intensity of OH(A2Σ+) changes less with increasing N2 volume fraction, which may be attributed to the lack of attachment reaction. Compared with Ar/NH3 DBD, the single discharge channel in He/N2 DBD is narrower, but the discharge area is wider, which should be induced by the higher Townsend ionization coefficient nonlinearity of He/N2 and the absence of attachment reaction in He/N2, respectively. In the end, a one-dimensional fluid model of Ar/NH3 DBD is built to verify the explanation of experimental results.

Photoelectric characteristics are an important reference for high-voltage discharges and are closely related to the excited mode of the high-voltage source. In this paper, we built a large-scale volume dielectric barrier discharge (DBD) system, which is composed of multilayer parallel-plate DBD electrodes and is excited by a high-voltage source in the power density modulation (PDM) mode. Subsequently, we analyzed the applied energy equation and evaluated the DBD systems photoelectric characteristics. The results show that the energy values of different applied voltage cycles during a PDM period exhibit significant differences. However, the average energy in a PDM period is approximately constant. Moreover, the equivalent capacitance of the DBD cell is a function of both the applied voltage and energy density. For the DBD cell, with the increase in both the applied voltage and energy loaded on the DBD cell, the total equivalent capacitance (C) is approximately constant, the dielectric capacitance (C d ) increases exponentially and decreases linearly, while the discharge gap capacitance (C g ) decreases and increases in the same cases. In addition, the relative intensities of the discharge emission increase and the energy efficiency ratios of the relative photoquantum yield of active species decline with the increase in both the applied voltage and energy density loaded on the DBD cell. The experimental results have been analyzed by evaluating the influence of the electrical parameters, and the underlying physical principles have been discussed. This paper clearly demonstrates that the photoelectric characteristics of the DBD reactor are significantly influenced by both the applied voltage and energy density, thus providing helpful insights into the energy evaluation and application of high-voltage discharges.

Summary form only given. Planar dielectric barrier discharges (DBDs) have a large number of industrial applications because of simple structure and no need for cumbersome impedance matching systems. However, planar DBD still have some disadvantages such as the limit of gap distance and the non-uniformity due to the characteristics of microdischarge intercepting electrodes. Therefore the DBD jet has been introduced. Other known atmospheric pressure plasma jet devices can generate very short plumes in the millimeter range. Recently Laroussi et al. developed a new plasma jet with long plume in the centimeter range. However, this type has difficulty in making large area plasma plume. Teschke et al. showed the possibility of long and large area plasma plume using coplanar DBD structure. Using coplanar DBD structure, we developed novel parallel DBD jet. The plasma source consisted of two coplanar DBD, which were made of two thin copper strips and alumina plate with 1 mm thickness. Each coplanar DBD was positioned as facing alumina plane with 1 mm gap. The helium was flowed into the gap with flow rate in the 10-40 l/min. A high voltage with frequency ranging from 1-30 kHz and amplitude up to 10 kV was supplied between two copper strips of each coplanar DBD. Experimental results showed the long and large plasma plume in the centimeter range. The length of the plume depended on the helium flow rate and the magnitude of the applied voltage

Feasibility and mechanism of removing Microcystis aeruginosa and degrading microcystin-LR by dielectric barrier discharge plasma