Pulsed streamer discharge characteristics of ozone production indry air

Experimental investigation of HV short pulsed streamer discharges in dry air-fed ozonizers under various operating conditions are reported. Ozone concentration, energy input and ozone production yield (efficiency) were measured at various voltages (14 to 37 kV), pulse repetition rates (25 to 400 pulses per second, pps), flow rates (1.5 to 3.0 1/min) and different gap spacings (10 to 20 mm) at a pressure of 1.01×10⁵ Pa in dry air. A spiral copper wire (1 mm in diameter) made to a cylindrical configuration (18 to 38 mm in diameter) in a concentric coaxial electrode system of various dimensions was employed. A magnetic pulse compressor provided the HV and current pulses. Higher voltage and higher repetition rates yielded higher concentrations of ozone at a fixed air flow rate. The present investigation was extended to assess the performance of this pulsed ozone generator using dry air under desired conditions of high concentration and high yield of ozone for industrial applications     

On the variety of triggering mechanisms of high-voltage breakdown in vacuum

The paper is devoted to study of the mechanisms responsible for vacuum breakdown as a whole and the total voltage effect in particular. Experiments at DC and pulsed voltages were carried out. It has been shown that there is no manifestation of the total voltage effect at DC voltages up to 20 kV. The strong dependence of hold-off on anode temperature was recognized at DC voltages while pulsed hold-off turned out to be almost the same with heating the electrodes. This gives a basis to consider gas desorption as an insufficient factor in the initiation of pulsed breakdown. An attempt to enhance hold-off with electrostatic removing of loosely bound particles with assistance of electron flow from a thermionic cathode was undertaken in the work. The approach turned out to be ineffective.     

Pulsed power production of ozone in O2/N2 ina coaxial reactor without dielectric layer

Very short duration pulsed streamer discharges have been used to produce ozone in a gas mixture of nitrogen and oxygen at atmospheric pressure. The ratio of nitrogen to oxygen in the mixture was varied in the range from 2.5/0.5 to 0.5/2.5, while maintaining a total flow rate of 3 l/min. The production of ozone was found to be higher for a specific mixture ratio of N₂/O₂ than that in oxygen or in dry air. The production of ozone in O₂ was higher than that in dry air. The production yield of ozone (g/kWh) increased with decreasing nitrogen in the O₂/N₂ mixture. It has been found that the peak of the streamer discharge current decreased with time after application of the pulsed power. This decrease in the current corresponded with the increase in the ozone production and is attributed to the loss of electrons in the discharge current due to their attachment to ozone to form negative ions     

复杂混合体等离子体反应器中相关因素对O3生成特性的影响

双脉冲放电等离子体水处理技术是一种有效的水处理方法,利用产生的活性物种能高效降解多种有机大分子污染物。针对复杂混合体等离子体反应器中气相O3生成情况进行了研究,重点考察了脉冲电压、曝入气体体积流量、不同的填料特性(粒径和表面粗糙度)等条件对水处理时生成O3的影响。实验结果表明,生成O3质量浓度随着放电电压增加而增大,随着曝入气体体积流量的减小而增加。填入不同粒径的填料生成O3质量浓度也有所不同,其中填充粒径9mm的填料时O3质量浓度最大。另外,粒径相同,但表面峰密度大的填料在生成O3时也表现出更好的特性。     

Improvement in ozone yield using discharge superposition method

The efficiency of ozonizers using silent discharge is very low compared with the theoretical value. Although many studies have attempted to improve the efficiency of ozonizers, we cannot expect to do so without changing the process of ozone generation. In this study, two high voltages are applied to an ozonizer which has three electrodes (central, surface, and outer electrodes) arranged coaxially, and the phase difference between applied voltages can be changed. The silent and surface discharges are superposed in the same space of the ozonizer. This paper considers the optimum experimental conditions leading to improved efficiency of an ozonizer using the discharge superposition method. It is found that when two kinds of discharges are superposed while using the central electrode as a common‐ground electrode, the maximum ozone yield efficiency is obtained, especially at a phase difference of about 180°. However, when using the surface electrode as a common‐ground electrode, the ozone efficiency is higher at phase differences of about 90° or 270° than at other angles. © 1998 Scripta Technica, Electr Eng Jpn, 126(1): 1–6, 1999     

Ozone production using pulsed dielectric barrier discharge inoxygen

The production of ozone was investigated using a dielectric barrier discharge in oxygen, and employing short-duration pulsed power. The dependence of the ozone concentration (parts per million, ppm) and ozone production yield (g(O₃)/kWh) on the peak pulsed voltage (17.5 to 57.9 kV) and the pulse repetition rate (25 to 400 pulses/s, pps) were investigated. In the present study, the following parameters were kept constant: a pressure of 1.01×10⁵ Pa, a temperature of 26±4°C a gas flow rate of 3.0 1/min and a gaseous gap length of 11 mm. A concentric coaxial cylindrical reactor was used. A spiral copper wire (1 mm in diameter) was wound on a polyvinylchloride (PVC) cylindrical configuration (26 mm in diameter) and placed centrally in a concentric coaxial electrode system with 4 mm thick PVC dielectric layer adjacent to a copper outer electrode of 58 mm in internal diameter. HV and current pulses were provided by a magnetic pulse compressor power source     

Ozone generation in dry air using pulsed discharges with andwithout a solid dielectric layer

Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide range of industrial applications. Ozonizers usually use dielectric barrier discharges and employ alternating current (ac) with consequent heat generation, which necessitates cooling. In the present study, very short duration pulsed voltage is employed resulting in reduced heating of the gas and discharge reactor. A comparison of ozone generation in dry air using a coaxial concentric electrode system with and without a solid dielectric layer is reported. Two types of dielectric layers were employed, ceramic and polyvinylchloride (pvc). The effects of peak pulsed voltage (12.5 to 62 kV), reactor length (0.1 to 1 m), pulse repetition rate (25 to 400 pulses per second, pps), gas flow rate (1.5 to 3.0 1/min) and variation of the pitch length of the spiral wire forming the central electrode (5 to 10 mm) on the concentration and production yield of ozone (g/kWh) are reported. A comparison is made between the performance of discharge reactors with (ceramic reactor Type IIC and pvc reactor Type IIP) and without (reactor Type I) a dielectric layer, using the same electrode gap separation (15 mm) and reactor lengths (0.157 and 1 m). High production yields of ozone in dry air of ~125 52 and 60 g/kWh were obtained when using, respectively ceramic, pvc, and no dielectric layer, for a fixed pulse rate of 100 pps, 15 1/min now rate and for a relatively short length of the reactor of 157 mm     

Industrial Applications of Pulsed Power Technology

A review of mainly the past two years is undertaken of the industrial applications of pulsed power. Repetitively operated pulsed power generators with a moderate peak power have been developed for industrial applications. These generators are reliable and have low maintenance. Development of the pulsed power generators helps promote industrial applications of pulsed power for such things as food processing, medical treatment, water treatment, exhaust gas treatment, ozone generation, engine ignition, ion implantation and others. Here, industrial applications of pulsed power are classified by application for biological effects, for pulsed streamer discharges in gases, for pulsed discharges in liquid or liquid- mixture, and for material processing.     

Measurement of space-charge distributions in insulators under veryrapidly varying voltage

In this paper we describe a new instrument for real-time measurements of space charge distributions in insulators submitted to rapidly varying voltages. It is illustrated with the pressure wave propagation method but can also be adapted for use with the pulsed electro-acoustic method. A new acoustic generator has been designed to produce high amplitude pressure pulses, at a high rate, and with good reproducibility. This generator, made of a thin transducer coupled with a waveguide and a backing medium, responds with a pressure pulse when a step voltage is applied. A special sample holder with a signal decoupling circuit, and a storage unit have been developed. The described instrument allows for measurements at a rate of 3200 Hz. Its potentialities are illustrated by studying the evolution of space charge in polyethylene samples stressed by both pulsed and 50 Hz ac voltages     

爆磁压缩发生器冲击高电压的测量

爆磁压缩发生器的负载一般没有良好的接地点,且远离测试仪器。笔者介绍了用双电阻分压器测量其负载冲击高电压的方法。该方法简单可靠,可以应用于没有良好接地和复杂危险环境下的冲击高电压的测量。     

液电效应催化臭氧氧化处理染料废水的研究

为了降低能耗和提高废水处理效果,解决臭氧在废水处理方面应用的一些实际问题,探讨了利用液电效应催化臭氧氧化废水的新工艺。用研制的一种小体积,低成本,操作方便,运行可靠的小能量脉冲功率电源进行了液电效应催化臭氧氧化处理活性艳红K2-BP水实验。实验结果表明:对4 L质量浓度200 mg/L活性艳红K2-BP溶液的处理,液电效应催化臭氧氧化比单独臭氧氧化脱色率提高了20个百分点,COD去除率提高了18个百分点;反应60 min后,活性艳红K2-BP吸收光谱的3个特征吸收峰均消失,发色基团及苯环和萘环均被打断。相同条件下脱色率达到90%,液电效应催化臭氧氧化比单独臭氧氧化电能节约41%(6.7Wh),氧气节约44%(24L)。证明此方法可提高臭氧利用率、增强染料脱色效果,减小装置体积,降低处理成本,具有良好的应用前景。     

双极性脉冲放电等离子体处理染料废水时化学需氧量去除效果相关因素分析

在双极性脉冲放电等离子体用于染料废水的降解过程中,废水化学需氧量(chemical oxygen demand,COD)的变化是在更深层次上反映该技术对有机污染物的降解能力的重要指标。为此,重点研究了在气液固三相混合体双极性脉冲放电条件下典型染料废水COD的去除规律,测试了不同电压、气体流量、初始浓度等条件下染料废水COD的变化。实验结果表明:当负载电压较高时,染料废水的COD值会先升高然后不断降低;而负载电压较低时,COD值会在一定程度内缓慢上升;气体流量越高,COD的去除效果越好;废水初始浓度增加,COD的去除率略有下降;初始电导率增加,COD的去除率降低;对具有不同官能团的染料废水进行放电处理发现,双极性脉冲放电对于各种结构的染料均有良好的处理效果。     

Behavioral characteristics of nanosecond pulsed discharge in coaxial electrodes

The environmental improvements by pulsed discharge plasma, a type of nonthermal plasma, have received much attention all over the world. The observation of discharge plasmas is beneficial for better understanding of the plasma physics of this growing field. Recently, nanosecond (ns) pulsed discharge with a short pulse duration of 5 ns achieved the higher energy efficiency on ozone generation and NO removal. However, the underlying mechanisms of these high efficiencies remain unclear. In the present study, the effects of electrode geometry on propagation process of ns pulsed discharge in coaxial electrodes were investigated using an ICCD camera. As the results, increasing wire diameters from 0.2 to 2.0 mm lead the different streamer discharge parameters; propagation velocity of streamer heads from 4.8 mm/ns to 12.5 mm/ns, peak of discharge current from 243 to 328 A, respectively. Therefore, it is concluded that the wire diameter is one of the paramount parameters to control the characteristics of the ns pulsed streamer discharge.     

纳秒脉冲下同轴内电极直径改变时闪络特性分析

在纳秒脉冲同轴电场下,尼龙1010和有机玻璃的闪络电压都随着内电极直径非线性增长,趋于饱和,且内电极直径越大,两者的闪络电压越接近.纳秒脉冲下沿面闪络特性与固体-液体-电极三结合点处的场强及沿面电位分布梯度紧密相关,内电极直径越大,三结合点处场强越低且沿面电位分布越均匀,引起沿面闪络电压越高.对于纳秒脉冲下的同轴电极,当内外电极半径差远大于内电极直径时,内电极直径变化对闪络电压的影响被弱化.     

多级磁压缩脉冲电源

阐述用于EUV光刻技术的脉冲功率电源的设计。该脉冲电源由充电电容组,半导体开关(IGBT),脉冲变压器和四级磁压缩回路组成。解释磁开关的工作原理,提供各关键元件的设计参数。根据磁性材料的物理特性参数,利用Pspice仿真软件建立磁芯模型,构建磁开关和仿真电路,对各级电压和电流波形进行分析,进而设计调整各级磁开关的参数。实验结果表明,该脉冲电源输出峰值为30 kV,上升沿为<85 ns,脉冲宽度<100 ns的脉冲信号。     

Simulation of Lag Phenomena and Pulsed I-V Curves of Compound Semiconductor FETs as Affected by Impact Ionization

Turn-on characteristics of GaAs MESFETs are simulated when the gate and the drain voltages are changed abruptly, and quasi-pulsed I-V curves are derived from them. It is discussed how the slow current transients (lag phenomena) and the pulsed I-V curves are affected by the existence of substrate traps and surface states. It is also discussed how the characteristics are influenced by impact ionization of carriers.     

Growth and characterisation of lead zirconate titanate (30/70) on indium tin oxide coated glass for oxide ferroelectric-liquid crystal display application

Abstract

The growth and characterisation of sol-gel lead zirconate titanate (PZT) (30/70) thin films on indium tin oxide (ITO) coated glass have been investigated using X-ray diffraction (XRD), transmitting electron microscopy (TEM) and atomic force microscopy (AFM). Perovskite crystallised at 550°C in a random orientation, and all films showed characteristic rosette formations. A seeding and crystallisation model has been proposed to describe the rosette formation process, which is based on the ease of PbO diffusion through the film. The effect of drying temperature on annealed film properties has been examined and when optimised has been shown to improve electrical properties and film flatness. Incorporation of the PZT films into small prototype liquid crystal displays has been done. Application of pulsed poling voltages to the displays has resulted in bulk alignment of the liquid crystal adjacent to poled regions of the PZT layer which remained after the poling voltages were removed.     

不同参数条件下水中脉冲放电的电学特性研究

在不同的电压和电导率参数条件下分类实验研究了水中脉冲放电的两种方式 (电弧放电和电晕放电 ) ,采集并分析了实验中的电压和电流数据。然后简要讨论了两种放电方式的产生机理 (与电弧方式的热过程机理相比 ,电晕方式的初始机理还很不清楚 )。最后从实验现象、产生机理和应用前景等方面对比分析了两种放电方式。实验发现在大的溶液电导率下水中电晕放电方式的声学效应明显 ,为水下等离子体声源的设计提供了新的思路。     

活性炭纤维在脉冲放电水处理中的催化作用

为了探索脉冲放电水处理反应器与活性炭纤维联合应用的可行性以及活性炭纤维在脉冲放电过程中的作用,将活性炭纤维加入气液串联放电反应器中对模拟污染物甲基橙进行了联合降解,并对活性炭纤维在脉冲放电过程中表现出的催化作用进行了研究。实验结果表明:脉冲放电和活性炭纤维联合处理,大幅度提高了降解率近24%,说明活性炭纤维与脉冲放电联合具有协同效应;脉冲放电和吸附饱和活性炭纤维联合处理与单独脉冲放电处理相比降解率提高16.7%,活性炭纤维的催化作用显著;加入H2O2对OH的形成具有增强作用,同时提高了UV和O3的利用率而且还有利于活性炭纤维的再生。     

Gas cleaning with semi-wet type plasma reactor

An experimental study on the removal of NH₃, NO, NO_x in concentration of 10-40 ppm in air has been carried out using plasma chemical reactions in a streamer corona discharge. The results of the performance of dry type and semi-wet type reactors are compared. The effects of different type of applied voltages such as rectangular pulse, 60-Hz sinusoidal, and 18-kHz alternating voltages are investigated. During NO removal, O₃ and NO₂ are produced. NO₂ can, partially, be removed with higher power input into the discharge. Another undesirable pollutant, namely N₂ O, is also produced, especially, in case of dry reactors having long residence time (~2.4 s). N₂O production decreases, essentially, to zero at 0.6-s residence time while using a semi-wet reactor. In general, higher removal efficiency has been obtained with pulse voltage in a semi-wet reactor. NH₃ in air appears to produce ozone and ammonium nitrate in a discharge. The performance of semi-wet reactors an the removal of submicron dust particles has also been investigated and very high removal efficiency (~93% at 0.6-s residence time) has been obtained