Influence of Power Modulation on Ozone Production Using an AC Surface Dielectric Barrier Discharge in Oxygen

The measurements of electro-optical discharge characteristics and concentration of produced ozone were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge (SDBD) in pure oxygen at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with a driving AC frequency of 1 kHz, variable discharge duty cycle of 0.01–0.8 and oxygen flow rate of 2.5–10 slm. We observed asymmetric SDBD behaviour as evidenced by the variation in the ratio of the O^I/O₂ ⁺ emission intensities registered during the positive/negative half-periods and complemented by the transferred charge measurements through the Lissajous figures. We also found a strong dependence of O₃ concentration on the discharge duty cycle. The highest calculated ozone production yield reached 170 g/kWh with a corresponding energy cost of about 10 eV/molecule when combining the lowest inspected duty cycle with the lowest AC high voltage amplitude.     

Influence of Duty Cycle on Ozone Generation and Discharge Using Volume Dielectric Barrier Discharge

The influence of duty cycle on ozone generation and discharge characteristics was investigated experimentally using volume dielectric barrier discharge in both synthetic air and pure oxygen at atmospheric pressure. The discharge was driven by an amplitude-modulated AC high voltage–power supply producing T_ON (a single AC cycle) and T_OFF periods with a widely variable duty cycle. The experimental results show that the energy delivered to the discharge during each AC cycle remains roughly constant and is independent of feed gas, duty cycle and T_OFF. Both average discharge power and ozone concentration show an initial linear increase with duty cycle, and deviate gradually from linearity owing to an increase in gas temperature at higher duty cycles. Nevertheless, ozone yield remains nearly constant (45.7 ± 3.5 g/kWh in synthetic air and 94.7 ± 3.1 g/kWh in pure oxygen) over a wide range of applied duty cycles (0.02–1). This property can be conveniently employed to develop a unique ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. Additionally, the discharges in synthetic air and pure oxygen have similar electrical characteristics; however, there are observable differences in apparent luminosity, which is weak and white-toned for synthetic air discharge, and bright and blue-toned for pure oxygen discharge.     

Ozone Production Using a Power Modulated Surface Dielectric Barrier Discharge in Dry Synthetic Air

The measurements of electrical and optical characteristics of the discharge and concentrations of produced ozone and nitrogen oxides were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge in dry synthetic air at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with driving AC frequencies of 1, 5 and 10?kHz, variable discharge duty cycle of 0.02?C0.8 and synthetic air flow rate of 2?C10?slm. The experimental results show that ozone and nitrogen oxides concentrations increased with increasing AC high-voltage amplitude, increasing discharge duty cycle and with increasing residence time. The highest calculated ozone production yield reached ~90?g/kWh with a corresponding energy cost of about 20?eV/molecule. The production yield was found to be independent of the driving AC frequency and specific energy density in the 10^?4?C10^?2?Wh/l range.     

三氧消毒杀菌与紫外线消毒杀菌效果的研究

对三氧消毒杀菌与紫外线对空气杀菌消毒的效果进行了比较，选择供应室无菌间的两间面积相同的房间，使用三氧消毒机和紫外线灯，照射到各自规定的时间进行空气采样，暴露15min后，置37℃培养24h，观察结果并进行菌落计数。结果表明，三氧消毒杀菌机的消毒作用优于紫外线灯，其消毒杀菌的安全性高，杀菌效果明确，是空气消毒理想的一种新型消毒方法。     

Generation Characteristics of Long-Lived Active Species in a Water Falling Film DBD Reactor

Plasma Chemistry and Plasma Processing - Water falling film dielectric barrier discharge (WFFDBD) has been widely studied for water treatment, due to its good performance on production of active...     

Measurement of Ozone Production in Non-thermal Plasma Actuator Using Surface Dielectric Barrier Discharge

Plasma actuators for flow control are intensively studied, but the production of ozone by the surface dielectric barrier discharge used in the actuators has never been quantified. Since ozone is harmful to human health, it is important to quantify its production for an application of this type of actuator on a land vehicle. This paper describes an experimental study to measure the concentration of ozone produced by an actuator with different parameters: amplitude and frequency of the applied high voltage, and the electrode configuration (shape, spacing and length). The results show that, under our experimental conditions, the production of ozone is directly proportional to the power dissipation. The production rate was measured at 21 g/kWh. Although the rate is much lower than that of an industrial ozonizer, it is still far from being negligible and should be taken into account for the future application of these actuators.     

Ethylene Epoxidation in an AC Dielectric Barrier Discharge Jet System

In this work, ethylene epoxidation was investigated in a dielectric barrier discharge jet (DBDJ) with a separate ethylene/oxygen feed under oxygen lean conditions. The ethylene (C₂H₄) stream was directly injected behind the plasma zone in order to reduce all undesired reactions, including C₂H₄ cracking and further reactions, while the oxygen (O₂) balanced with argon was fed through the plasma zone totally to maximize the formation of active oxygen species. The effects of various operating parameters, such as total feed flow rate, O₂/C₂H₄ feed molar ratio, applied voltage, input frequency, and C₂H₄ feed position on the ethylene epoxidation activity, were investigated to determine the optimum operating conditions for this new DBDJ system. The highest ethylene oxide (EO) selectivity (55.2 %) and yield (27.6 %), as well as the lowest power consumption (3.3 × 10^?21 and 6.0 × 10^?21 Ws/molecule C₂H₄ converted and EO produced, respectively) were obtained at a total feed flow rate of 1,625 cm³/min (corresponding to a residence time of 0.022 s), an O₂/C₂H₄ feed molar ratio of 0.25:1, an applied voltage of 9 kV, an input frequency of 300 Hz, and a C₂H₄ feed position of 3 mm behind the plasma zone. The superior activity of the ethylene epoxidation in the DBDJ system resulted from a small reaction volume as well as a separate ethylene/oxygen feed.     

Air Supply Mode Effects on Ozone Production of Surface Dielectric Barrier Discharge in a Cylindrical Configuration

Plasma Chemistry and Plasma Processing - We investigated the air supply mode effects on ozone production of the surface dielectric barrier discharge in the cylindrical configuration. The air into...     

臭氧的应用及产生技术

主要阐述了臭氧的性质、用途及产生技术,并重点介绍了臭氧的用途和臭氧产生技术的现状。     

Experimental Study of Nitrogen Oxides and Ozone Generation by Corona-Like Dielectric Barrier Discharge with Airflow in a Magnetic Field

We investigated nitrogen monoxide, nitrogen dioxide and ozone generation for corona-like dielectric barrier discharge in a stationary magnetic field with airflow. The magnetic field was produced by the permanent magnet. We showed that nitrogen monoxide could be easily generated at relatively low voltages, by application of a magnetic field on the hollow needle to mesh with a dielectric barrier discharge. For higher voltages generation of nitrogen monoxide falls to zero, and generation of nitrogen dioxide and ozone with increasing voltage increases. We also demonstrated that simultaneous application of the magnetic field with airflow through the needle electrode affects the transition of the discharge from the high to the low voltage regime. This transition is accompanied by important changes in the production of nitrogen oxides and ozone. Changes in the discharge regime are reflected by changes in the voltage–current waveforms. The obtained results could be interesting for various biomedical applications or bacterial decontamination of surfaces.     

交流碳弧法合成碳包碳化铁纳米晶

采用交流碳弧法高效合成碳包碳化铁纳米晶磁性微粉,磁性微粉产率达90%以上.用热重分析法(TG)测得磁性微粉中Fe的质量分数为17.5%.X射线衍射(XRD)分析结果表明,在碳包碳化铁微粉中存在Fe₃C和Fe₅C₂两种结构形式,不含纯Fe晶粒,碳层结构与石墨相似.在透射电镜(TEM)下观察了纳米晶的形貌和粒径分布,碳化铁纳米晶尺寸分布在3～10nm,并呈颗粒状分散在碳层中,碳层为巴基管和巴基葱的堆积体,形状各异,尺寸分布在几十纳米到几微米之间.讨论了碳包碳化铁纳米晶的形成机理.测定了磁性微粉的磁滞回线,其饱和磁感应强度Bs,剩磁Br和矫顽力Hc分别为2.6×10^-2T,2.5×10^-3T和5.52kA/m.     

The Mutual Conversion of CO2 and CO in Dielectric Barrier Discharge (DBD)

Non-equilibrium plasma, which was engendered by dielectric barrier discharge (DBD) was used to analyze the mutual conversion between CO₂ and CO. The results showed that the conversion ratio of CO increased monotonously with the increasing voltage. But CO₂ was not so. Its conversion ratio reached maximum when the voltage was 3600 V in Ar system. It also showed that the existence of water molecules was more advanageous for the conversion of CO to CO₂ in Air system than in oxygen system, and the conversion ratio could reach 75.8% when the relative humidity was 100%. We also discussed the energy yield and energy efficiency, and the result was that high voltage and high concentration of reactant was disadvantageous for energy utilization.     

An Ozone Generator of Miniaturization and Modularization with the Narrow Discharge Gap

The method of ionization discharge has a key action on the process of the ionization and decomposition of O₂ molecule as well as the re-decomposition of O₃ molecule. In this paper, an ozone generation of miniaturization which was fabricated by stacking discharge modules with rectangle is introduced, only volume of 23.0×53.0×42.0 cm³ for ozone production capacity of 1 kg/hr. In addition, the ozone concentration and its production efficiency are significantly improved in comparison with a conventional ozone generator, which have the highest ozone concentration of 308 g/Nm³ and the production efficiency of 118 g/kWh at ozone concentration of 200 g/Nm³.     

Plasmas in Saline Solution Sustained Using Bipolar Pulsed Power Source: Tailoring the Discharge Behavior Using the Negative Pulses

Plasmas in saline solution driven by a repetitive bipolar pulsed power source are studied. We use a negative pulse to generate electrolytic gas with a controllable amount, followed by a positive pulse to ignite the plasma. With an increase in the negative voltage pulse amplitude from 0 to ?80 V, we observed an increase in the amount of electrolytic gas (hydrogen) formation, resulting in a reduced time delay, from 65 to 6 μs, required to ignite the plasma upon the onset of the positive pulse. A decrease, from 1.75 to 1.0 A, in the peak currents within the positive voltage pulse is also observed. Optical emission spectroscopy shows that the intensity ratio of the H_α (656 nm) to Na (588 nm) emission lines increases from zero to 0.0035. These observations can be well explained by the increase in the gas coverage on the electrode surface and the change in the gas composition within which the plasma is ignited with the application of the negative pulse.     

Direct Oxidation of Methane to Methanol Over Cu-Based Catalyst in an AC Dielectric Barrier Discharge

In this paper, the conversion of methane to methanol on CuO/Al₂O₃ and Mo–CuO/Al₂O₃ catalysts in a plasma reactor was tested. A comparison between catalytic and plasma-catalytic systems had been made in tested temperature range of 50–300°C. Experimental results showed that plasma-catalytic system demonstrated a much better methane conversion than catalytic system in tested temperature range and Mo–CuO/Al₂O₃ revealed a higher catalytic activity than CuO/Al₂O₃ for methanol synthesis. Furthermore, an Arrhenius plot was made in order to deduce the mechanism of plasma activation, which revealed that the presence of plasma decreased the activation energy for both catalysts. In the case of Mo-CuO/Al₂O₃ catalyst, the enhanced activity for methanol synthesis was assumed due to the oxygen vacancies on Mo–CuO/Al₂O₃ catalyst, which can utilize plasma-induced species to improve the catalytic efficiency.     

Ozone Production in the Negative DC Corona: The Dependence of Discharge Polarity

The rate of production and the spatial distribution of ozone in the negative DC corona discharge are predicted with a numerical model. The results are compared to prior experimental data and to results previously presented by the authors for the positive corona discharge. In agreement with experimental data, ozone production rate in the negative corona is an order of magnitude higher than in the positive corona. The model reveals that this significant difference is due to the effect of discharge polarity on the number of energetic electrons in the corona plasma. The number of electrons is one order of magnitude greater and the chemically reactive plasma region extends beyond the ionization region in the negative corona. The paper also extends our prior modeling effort to lower velocities where the Joule heating reduces ozone production. The magnitude of the reduction is characterized by a new dimensionless parameter referred to as the electric Damkohler's third number(Da_III–e).     

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device,Discharge Characteristics and Modes of Operation

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current–voltage and discharge characteristics were measured for hydrogen-chlorate membrane–electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge. We established that chlorine dioxide (ClO₂) is the key intermediate product; its fraction in the electrolyte solution increases progressively, up to its maximum, equal to 0.4–0.6 of the initial amount of chlorate anions, whereas the ClO₂ amount decreases gradually to a zero value in the later stage. In most discharge experiments, the Faradaic yield exceeded 90% (maximal value: 99%), providing approximately 48% chemical energy storage-to-electricity conversion efficiency at maximal power of the discharge (max value: 402 mW/cm²). These results support prospect of a hydrogen-chlorate flow current generator as a highly specific energy-capacity source for airless media.     

Ozone Production in the Positive DC Corona Discharge: Model and Comparison to Experiments

A numerical model of ozone generation in clean, dry air by positive DC corona discharges from a thin wire is presented. The model combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction in the air stream. The distributions of ozone and nitrogen oxides are obtained in the neighborhood of the corona discharge wire. The model is validated with previously published experimental data. About 80% of the ozone produced is attributed to the presence of excited nitrogen and oxygen molecules. A parametric study reveals the effects of linear current density (0.1–100 A/cm of wire), wire radius (10–1000 m), temperature (300–800 K) and air velocity (0.05–2 m/s) on the production of ozone. The rate of ozone production increases with increasing current and wire size and decreases with increasing temperature. The air velocity affects the distribution of ozone, but does not affect the rate of production.     

Influence of the Outer Electrode Material on Ozone Generation in Corona Discharges

The effect of the outer electrode material on negative corona discharge current and the process of ozone formation have been studied in coaxial cylindrical system of electrodes fed by dry oxygen. Three materials (brass, duralumin, stainless steel) were tested in experiments. The probability coefficient of ozone decomposition was found be slightly higher compared with known data. The coefficient of probability of ozone decomposition is decreasing with the time of exposition of the metal surface to mixture of oxygen and ozone. The effect of the electrode material on the current voltage characteristic of the discharge was marginal. In contrast to this at average energy density η higher than 10 J/cm³ the ozone concentration is affected by material of the outer electrode. A strong influence of the temperature of metal electrode on the probability coefficient of ozone decomposition was illustrated from the decrease of the ozone production.     

Plasma Catalytic Synthesis of Ammonia Using Functionalized-Carbon Coatings in an Atmospheric-Pressure Non-equilibrium Discharge

We investigate the synthesis of ammonia in a non-equilibrium atmospheric-pressure plasma using functionalized-nanodiamond and diamond-like-carbon coatings on α-Al₂O₃ spheres as catalysts. Oxygenated nanodiamonds were found to increase the production yield of ammonia, while hydrogenated nanodiamonds decreased the yield. Neither type of nanodiamond affected the plasma properties significantly. Using diffuse-reflectance FT-IR and XPS, the role of different functional groups on the catalyst surface was investigated. Evidence is presented that the carbonyl group is associated with an efficient surface adsorption and desorption of hydrogen in ammonia synthesis on the surface of the nanodiamonds, and an increased production of ammonia. Conformal diamond-like-carbon coatings, deposited by plasma-enhanced chemical vapour deposition, led to a plasma with a higher electron density, and increased the production of ammonia.