Dielectric Barrier Discharge Type Research Articles

Characteristic of Thermal Decomposition of Ozone

In general, dielectric barrier discharge (DBD) typed ozone generators are used for water treatment including drinking water and wasted water. Recently, it has been reported that composed ozone concentration by DBD type ozone generator decreases with time using high purity oxygen as a fed gas. The phenomenon is called “Ozone Zero Phenomenon”. As one of factors responsible for the occurrence of this phenomenon is speculated to be an influence from electrode surface, we have focused our investigation on electrode surface heating generated by electrical discharge. Rate of thermal decomposition of ozone by heated stainless steel (SUS) pipe and Pyrex glass pipe were evaluated by ozone concentrations at inlet and outlet of heated pipes. As a result, for temperature of heated both pipes below 120°C, thermal decomposition of ozone was not confirmed in each transit time (0.25-1.5s). However, when both heated pipes are over 160°C, thermal decomposition of ozone was found and the rate of ozone decomposition increased depend to transit time in heated pipes. It was thought that there were at the least 2 processes of decomposition of ozone: one is oxidation of surface of pipes, and another is thermal decomposition in gas phase. The former is enhanced at the stepwise increase of ozone concentration in stainless steel pipe below 160°C compare with Pyrex pipe. The temperature above 180°C, thermal decomposition is increased against the time in the both kind of pipes. This is considered decomposition of ozone in gas phase.

Ozone Zero Phenomenon in Ozone Generator Equiped with Coaxial Cylinder Electrodes Covered by Dielectrics

Ozone generators of dielectric barrier discharge (DBD) are mainly used for water and waste water treatment. Recently, they are also used for cleaning of food product machines, semiconductors processes, pulp bleaching field and so on. It is well-known that ozone concentration composed by DBD type ozone generator decreases with time when high purity oxygen used for feed gas. This is named by us, ozone zero phenomenon (OZP). The causes of the phenomena have been investigated experimentally in the world wide industries us. One of the causes is considered as an electrode material by discharge in the generator metal oxides formed from stainless steel electrode. We have studied the ozone generation characteristics using high purity oxygen as a feed gas and ozone generator of which both electrodes covered with dielectrics. It was found that using only high purity oxygen as a feed gas, ozone concentration decreased from 200g/m3(N) to 54g/m3(N) during about 5 hours. However, adding 0.1vol% of nitrogen into oxygen, ozone concentration increased rapidly over the initial maximum ozone concentration of 216g/m3(N). After that, the concentration of ozone gradually decreased with time. Therefore, adding nitrogen into oxygen has the effect of recovery of ozone concentration in the same generator. The maximum ozone concentration was obtained when 0.1-0.6vol% of nitrogen gas was added to oxygen gas. OZP is caused by ozone generator even when both electrodes are covered with dielectrics. The metal oxide is produced on electrode is not the cause of OZP. Ozone concentration can be increased by adding nitrogen into oxygen.

Design of a current converter to maximize the power into homogeneous dielectric barrier discharge (DBD) devices

Dielectric Barrier controlled Discharges (DBD) are able to produce low temperature plasmas at atmospheric pressure. DBD are used since a long time for various industrial applications. In the surface treatment industry, even though it is widely used, the reproducibility of the surface treatment process, called corona, is limited due to the type of DBD used, which is a filamentary one. Under specific experimental conditions (frequency and amplitude of the applied voltage, gas type, ) the discharge is homogeneous like low-pressure plasmas. The type of discharge is of great interest for thin film deposition. However, the treatment time is still too long for an online process. To reduce the treatment time, the discharge power must be increased. In this paper, we show that supplying a homogeneous DBD in nitrogen with a current controlled power source is a better alternative than sinusoidal voltage source. It allows to maximize injected power accurately control the injected power. Such a power converter especially designed for experimental validation purposes is then studied.

Study on Surface Modification of GaN by Atmospheric Microplasma

GaN is widely studied and developed as a material for new application in power electronic devices or as an emitter of various colors of light. GaN is usually formed by nitriding GaAs and grown on the sapphire substrate with a high dislocation density. For this dislocation, microchannel epitaxy or regrowth of GaN is required to reduce dislocations. Recently, plasma treatment has been used for interface treatment, regrowing of GaN crystal, and nitridation process of GaAs. GaN surface was treated by atmospheric-pressure microplasma using Ar and N2 as process gases and powered by ac and pulsed-power supplies. Microplasma is atmospheric-pressure nonthermal plasma and a type of dielectric barrier discharge which has a small discharge gap and requires relatively low discharge voltage of only about 1 kV. Modifications of the surface were observed after the treatment, and they depend on the gas process, treatment time, and power supply. The surface was analyzed before and after the treatment using X-ray photoelectron spectroscopy analysis and atomic force microscopy.

Study on the factors influencing phenol degradation in water by dielectric barrier discharge (DBD)

Dielectric barrier discharge (DBD) is an effective method to produce active species including ozone for remediation of pollutants in water, gas, etc. In the present work, a DBD type surface discharge system was utilised to degrade phenol in solutions. The influence of experimental conditions including solution pH values, initial concentration of phenol and applied voltage on the degradation rate of phenol, the removal of COD and the byproducts was examined and discussed as well as the concentration change of ozone during phenol was examined. Experimental results reveal that high pH value advanced the degradation of phenol and COD removal, which maybe contributed to the enhanced generation of hydroxyl radicals under higher pH value; applied voltage influenced the transformation of phenol to byproducts which could be demonstrated by the different COD removal under different applied voltages. Under an optimization condition, the degradation rate of phenol reached 100% in 80 minutes and COD removal reached 68% in 120 minutes.

Ozone Production Characteristics in a Dielectric Barrier Discharge Type Ozonizer Driven by Pulsed Power

Ozone has many applications in various fields with an advantage of low environmental load, i.e., water treatment, sterilization, deodorization, bleaching, etc. While the dielectric barrier discharge (DBD) is mainly used for practical ozone generator, the various discharge methods have been studied to achieve higher yield and higher concentration of ozone generation in recent years. This study is carried out to compose ozone using a Blumlein type pulse forming network (B-PFN) as a discharge power source combined with the ordinary DBD type ozone generator. The ozone generator is equipped a pair of coaxial cylinder electrodes. The inner electrode is stainless steel cylinder and is applied pulsed voltage. The outer electrode is covered by glass lining of inner surface of electrode and is act as earthed electrode. This generator gives maximum ozone concentration of about 57g/Nm3 by negative polarity and maximum ozone yield of about 900g/kWh by positive polarity. These results are compared with other results using pulsed power discharges. We also investigated temporal variation of ozone concentration, related to “Ozone zero phenomena”.

0809 同軸円筒型DBD チューブによる噴霧流中難分解性有機物の分解(OS8-2 機能性流体工学の融合化新展開,OS8 機能性流体工学の融合化新展開)

The technology of non-thermal plasma contacting with liquid has been paid attention for water treatment because of free radical generation. The advanced oxidation processes (AOPs) utilizing free radicals have been developed to decompose persistent organic pollutants (POPs). In this study, the water treatment method spraying solution into the coaxial cylinder type dielectric barrier discharge (DBD) tube is investigated. The reactor is an alumina tube with 2 mm thickness and 6 mm inner diameter. The reactor has inner powered rod electrode on the central axis of tube and outer grounded electrode on the outer wall of tube. The solution is atomized by the ultrasonic atomizer unit and introduced into the reactor. Acetic acid solution is used as POPs in this experiment. Acetic acid is decomposed in high efficiency and formic acid and oxalic acid are formed as by-products for one pass treatment.

Reactive fluxes delivered by dielectric barrier discharge filaments to slightly wounded skin

The application of atmospheric-pressure plasmas to human tissue has been shown to have therapeutic effects for wound healing and in treatment of skin diseases. In this paper, we report on a computational study of the intersection of plasma filaments in a dielectric barrier discharge (DBD) with a small wound in human skin in the context of plasma medicine. The wound is represented as a small cut in the epidermal layer of cells. Intracellular structures and their electrical properties were incorporated into the two-dimensional computational mesh in order to self-consistently couple gas phase plasma transport with the charging of the surface of the wound. We quantify the fluxes of reactive oxygen and nitrogen species, ions and photons produced in or diffusing into the wound as might occur during the first few discharge pulses of treatment. Comparison is made to fluxes predicted by global modelling. We show that the relative location of the plasma filament with respect to the wound is important on plasma time scales (ns) for ions and photons, and for radicals directly produced by electron impact processes. On the longer-term diffusion time scales (ms) the position of the plasma filament relative to the wound is not so critical. For typical DBD conditions, the magnitude of these fluxes to the cellular surfaces corresponds to fluences of radicals nearly equal to the surface site density. These results imply that the biological reactivity is limited by reaction probabilities and not the availability of radical fluxes.

Experiment Research of Solar Energy Ozonizer Used in Sewage Treatment

The device is composed of solar battery, power automatic switching, high pressure booster inverter, dielectric-barrier discharge type ozonizer, air compressor and microporous aerator components, whicn is powered by the double power suppl y modes including the solar battery and the city electricity. In the conditions of insufficient illumination or rainy weather, power can switch to the city electricity automatically. The article introduces the composition and working principle of solar ozonizer. The experiment is respectively done in the sample of the second phase of water from BaoDingYingdingzhuang sewage plant, the urban river water and the dyeing effluent with 1500 ml.The power of the solar energy ozonizer is 18W and ozone production is 25 mg/min. The experiment results show that the removal rate of Fecal coliform, Chroma and Chemical Oxygen Demand (COD) are obviously improved. Especially, the removal effect of Fecal coliform and Chroma is very significant. The experiment indicates that the content of NH3-N has increased with the growth of ozone contact time.

Surface Modification of GaN Substrate by Atmospheric Pressure Microplasma

In this study, surface modification of GaN substrates by microplasma was investigated. Microplasma, which is an atmospheric pressure nonthermal plasma and a type of dielectric barrier discharge, was generated with a pair of electrodes that were covered with a dielectric layer and that faced each other at a small discharge gap under 100 µm with a spacer. Owing to small discharge gaps (0–100 µm) and to the assumed specific dielectric constant of εr = 104, a high-intensity electric field (107–108 V/m) could be obtained with a relatively low discharge voltage of only about 1 kV at atmospheric pressure. The GaN surface was treated with atmospheric pressure microplasma using Ar and N2 as process gases and powered by AC and pulse power supplies. Modifications of the surfaces were observed after the treatment and they depend on the gas process, treatment time, and power supply. The surface was analyzed before and after the treatment by X-ray photoelectron spectroscopy (XPS) analysis and Field-emission scanning electron microscopy (FE-SEM).

Promoted cell and material interaction on atmospheric pressure plasma treated titanium

Surface carbon contamination is a natural phenomenon. However, it interferes with cell–biomaterial interaction. In order to eliminate the interference, atmospheric pressure plasma treatment was employed. Dielectric barrier discharge treatment of titanium surface for less than 10min turned titanium super-hydrophilic. Adsorption of fibronectin which is the major cell adhesive protein increased after plasma treatment. Cell attachment parameters of osteoblast cells such as population, cell area, perimeter, Feret's diameter and cytoskeleton development were also enhanced. Cell proliferation increased on the plasma treated titanium. In conclusion, dielectric barrier discharge type atmospheric pressure plasma system is effective to modify titanium surface and the modified titanium promotes cell and material interactions.

A combined process of non-thermal plasma with sludge stabilization for the simultaneous reduction of odor and organic waste

Odor emissions and sludge disposals have become most challenging issues in many sludge treatment plants, and separate chemical oxidation processes have been commonly employed for these problems. It is, therefore, necessary to develop a combined process that simultaneously reduces the odor emissions and the amount of waste sludge. In this study, a non-thermal plasma reactor using a dielectric barrier discharge type was employed to treat a gas stream contaminated with 10 ppm(v) of H(2)S, and then the ozone-laden gas stream was supplied to a sludge stabilizer to reduce the organic constituents. The specific energy input to the plasma was varied to investigate the performance of the combined process. When the specific energy inputs were 200, 260, and 360 J/L, the rates of ozone generation from the plasma reactor were 0.036, 0.070, 0.144 g-O(3)/h, respectively. At these experimental conditions, the removal efficiencies of H(2)S were 60, 75, and >99%, and total chemical oxygen demand (TCOD) reduction efficiencies of 33, 61 and 67% were observed. In addition, a soluble organic fraction of the sludge increased at ratios of 1.9, 8.9, and 10.7%, respectively. Consequently, the combined process effectively and simultaneously reduced the odor compounds as well as the organic constituents and particles in the waste sludge.

Effect of low-temperature plasma treatment on tailorability and thermal properties of wool fabrics

Dielectric barrier discharge type of plasma reactor was used for the low-temperature plasma (LTP) treatment of the wool fabrics. Air was used as the non-polymerizing gas for the plasma treatment at different time intervals. Low-stress mechanical properties of the treated and untreated wool fabrics were evaluated using Siro-fast technique which revealed that the tensile, bending, compression, shear, dimensional stability and surface properties were altered after the LTP treatment. Other properties such as thermal conductivity, thermal resistance and pilling propensity were also evaluated. The surface topographical changes of the wool fibres after LTP treatment were analysed by scanning electron microscopy. The changes in these properties are supposed to be related closely to the interfibre and interyarn frictional force and increased surface area of the fibres induced by the etching effect of plasma.

Plasma assisted heterogeneous catalytic oxidation of carbon monoxide and unburned hydrocarbons: Laboratory-scale investigations

The use of upstream plasma treatment and ozone injection for the amelioration of the performance of diesel oxidation catalysis was investigated. Experiments presented here were performed in preparation for full scale tests on diesel engines. A significant augmentation of the oxidation rate of carbon monoxide was observed when plasma was applied upstream of a diesel oxidation catalyst and was attributed to a heterogeneous reaction of ozone with carbon monoxide. This observation led to ozone injection being investigated as an alternative to the direct application of dielectric barrier discharge type plasma to the gas upstream of the diesel oxidation catalyst. Results are presented about the two modes of the combination of the non-thermal plasma with the catalyst when they were applied during the catalyst light off, and are compared in terms of pollutant removal and energy cost for carbon monoxide and hydrocarbons. Mechanisms for these effects are proposed and the performances of the two approaches are discussed.

Effect of plasma chemistry on the simulation of helium atmospheric-pressure plasmas

The effect on the selection of different plasma chemistries for simulating a typical dielectric barrier discharge (DBD) driven by quasi-pulsed power source (20 kHz) is investigated. The numerical simulation was performed by using the one-dimensional self-consistent fluid modeling solver. Our simulation result indicates that the computed temporal current density can be significantly improved by using a complex version of plasma chemistry module rather than the simple one and demonstrates an excellent agreement with the experimental data. The result suggests the metastable, excited and ionic helium related reaction channels, which are important in simulating a DBD, should be taken into account. Furthermore, it also reveals that the power absorption of ions is considerably higher than that of the electron.

Development of a Remote-from-Plasma Dielectric Barrier Discharge Ion Source and Its Application to Explosives

The design of a new type of dielectric barrier discharge (DBD) ion source for ambient ionization is described. In this ion source, the DBD plasma is confined in the DBD tube so that the sample gases can be ionized just outside of the discharge tube by DBD excited helium gas without being exposed to the plasma jet. The findings indicate that the ion source is capable of the soft and high-sensitive ionization of explosives.

1312 小型平板翼形状プラズマアクチュエータの誘起流特性のPIV計測(OS13-2 流れの抵抗低減,オーガナイズドセッション)

Research interest in plasma actuator is increasing day by day in the field of fluid dynamics. Various types of plasma actuators are used for various research purposes. In most cases, the plasma actuator is based on a surface dielectric barrier discharge (DBD), the flow is produced between two electrodes mounted on both sides of a dielectric material and can be used in flow control applications due to the momentum transfer from the plasma species to the fluid. This paper investigated floating type DBD plasma actuators in the absence of external flow by means of particle image velocimetry. The electric wind was generated by a single DBD excited by a sine wave of 5 kHz. The induced flow was compared by changing the distance from the leading edge to the actuator position.

On the Scale-Up of Uneven DBD Reactor on Removal of Diesel Particulate Matter

The scale-up of an uneven type of dielectric barrier discharge (DBD) reactor driven by a positive–negative pulse power supply for the removal of particulate matter (PM) from a diesel engine has been carried out. The scale of the uneven DBD reactor was changed by using three kinds of reactors consisting of 20, 30, or 50 pairs of uneven alumina and stainless steel plates. In this study, relations of energy injection into the above DBD reactors, PM removals, PM removal efficiencies with pair numbers have been investigated. The parameters in the kinetic model used to describe the PM removal are given.

Basic Characteristics of Dielectric Barrier Discharge Reactor Using Anodic Porous Alumina for NOx Removal

Dielectric barrier discharge (DBD), properly combined with porous ceramics and/or catalysts, is a promising technology for diesel exhaust gas treatment. In this study, anodic porous alumina, which has numerous pores with nanometer-order diameter and a high aspect ratio, has been examined for use as a barrier in a DBD reactor. The anodic porous alumina greatly improves the DBD reactor. Nevertheless, few reports describe DBD using the anodic porous alumina barrier. As described herein, the DBD reactor’s basic characteristics and NOx removal in atmospheric pressure air were studied to support its future development. Results were compared with those of a typical DBD to clarify the influence of anodic porous alumina on those characteristics.The electropolished 99.99% pure Al substrate was anodized in 1.0 M sulfuric acid of 10°C for 5 h at dc 24 V. The Al substrate and anodic porous alumina respectively act as the electrode and dielectric barrier of the DBD. The dry gas mixture of NO (several hundred ppm) / O2 (20%) / N2 was supplied into the DBD reactor at 1.0 L/min. The resultant voltage and current waveforms resembled those of a typical DBD. Results revealed that NO was mostly oxidized to NO2 ; about 20 ppm N2O was detected. Different from a typical DBD the NO2 increased characteristically as a function of operation time.

Experimental study on repetitive unipolar nanosecond-pulse dielectric barrier discharge in air at atmospheric pressure

Dielectric barrier discharge (DBD) is a typical approach for producing non-thermal plasma at atmospheric pressure. In this experimental study, the DBD is excited by repetitive unipolar nanosecond pulses with a rise time of ∼15 ns and a full-width at half-maximum of ∼30 ns. With a unipolar pulse voltage of 35 kV, the measured discharge current across the DBD circuit has a positive and negative pulse, and the pulse peak value can be hundreds of amperes. The low-speed camera images of the discharge show that both diffuse ‘glow-like’ and filamentary discharges can be observed, and the air gap length, barrier variety and applied repetition rate are the important factors influencing the transition of the two discharge modes. According to a known equivalent circuit and measured data of a typical DBD, electrical parameters including voltage, current and instantaneous power across the air gap and dielectric layer are calculated. The calculated results indicate that there are two consecutive discharges in the air gap, and the secondary discharge fires immediately after the primary discharge extinguishes. The power consumption of the secondary discharge is provided by the dielectric layer and deposited during the primary discharge. With the increase in the repetition rate, the energy deposition in the air gap per second is greatly enhanced and can exceed one joule for a repetition rate up to 100 Hz, and the corresponding charge transfer is also increased. The electron temperature and density are estimated to be approximately 5.1 eV and 1.6 × 1012 cm−3, respectively.