Sterilization efficacy of a coaxial microwave plasma flow at atmospheric pressure

A coaxial cable for microwave transmission type of atmospheric low-temperature plasma source was developed. The plasma source has the advantages of portability, simple configuration, and ability to operate with a wide range of gases and mixtures of such gases. It mainly consists of a cavity, a quartz discharge tube, a coaxial cable, a microwave power source, and a gas supply system. Using this plasma source, the authors tried to clarify its sterilization efficacy against Geobacillus stearothermophilus. A log reduction number of G. stearothermophilus of at least 5 (10/sup -5/) was obtained under the following operating conditions: gas flow rate of argon of 14 SL/min, input power is 400 W, and substrate surface temperature of 353 K. Distributions of temperature and velocities of gas were also measured two-dimensionally by using an E-type thermocouple and a Pitot tube, respectively. The temperature distributions and the peak value of temperature were found to be influenced by the gas flow rate and the kinds of gas mixtures.     

Basic characteristics of Ar/N2 atmospheric pressure nonequilibrium microwave discharge plasma jets

To understand the mechanism of surface processing by atmospheric pressure nonequilibrium microwave discharge plasma jets of coaxial type without a resonator, we measured the vibrational and rotational temperatures in plasmas using optical emission spectroscopy. The plasma was excited by a microwave power supply, using a gas mixture of Ar and N₂ as the plasma gas, and changing the flow rate of N₂ gas. We also measured the change in the contact angle of a PET film before and after the plasma processing. It decreased as the plasma rotational temperature increased, indicating that the hydrophilicity of the PET surface was improved as the plasma rotational temperature became higher. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

预电离大气压低温等离子体射流及其在表面清洗中的应用

具有高化学活性的大气压放电低温等离子体射流具有潜在的应用价值。为此,介绍了一种利用预电离办法产生Ar/O2等离子体大气压低温射流及其在表面油污清洗中的应用。采用针电极放电等离子体作为预电离源,为射流介质阻挡放电(DBD)提供种子电子,使得射流DBD的击穿与维持电压得以降低,即使在氧气与氩气体积比高达6%时,也可以产生均匀稳定的放电模式。采用光纤温度传感器检测得到放电等离子体气体温度在390～440K,而Boltzmann斜率法计算得到的电子激发温度为4640K,通过示踪元素法计算得到氧原子数密度在1017 cm-3量级。将该射流应用到玻璃表面油污清洗,最大清洗速率可达0.1mm/s。所以预电离技术可以产生具有高化学活性的均匀放电的大气压低温等离子体射流,该射流在表面油污清洗中具有较高效率。     

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     

Hysteresis effect of corona discharge in a narrow coaxial wire-pipedischarge tube with gas flow

An experimental investigation has been conducted to study corona discharge in a narrow tube. Narrow or capillary corona discharge (discharge tube diameter d≈1-20 mm) is used for many industrial applications such as flue gas cleaning corona-induced plasma reactors, ion sources, and electrohydrodynamic heat exchangers. In this work, corona discharge characteristics of a narrow coaxial wire-pipe discharge tube with gas flow are experimentally investigated. The results show that, unlike normal corona discharge, a hysteresis in the corona discharge current-voltage characteristic was observed for narrow tube discharges. The onset of the corona discharge was observed to be significantly dependent on the gas temperature and gas flow rates     

Reduction of NOx from combustion flue gases bysuperimposed barrier discharge plasma reactors

NO_x reduction from combustion flue gases by superimposed barrier discharge plasma reactors is experimentally investigated. The experiments are conducted for applied voltages from 0 to 28 kV, flue gas rates from 0.5 to 2 L/min, ammonia mixture concentrations from 0.7 to 2.65 stoichiometry, and applied voltage phase differences from 0° to 180°, where two 60-Hz AC power supplies are used. The results show the following: (1) NO_x reduction rate decreases with increasing discharge power for surface discharge operations, however, NO_x reduction rate increases with increasing discharge power for silent and superimposing discharge operating modes; (2) NO_x reduction rate increases with increasing discharge power, gas flow rate and ammonia stoichiometry under in-phase operations; (3) NO_x reduction rate for out-of-phase operations is much higher compared with in-phase operations, however, NO_x reduction rate has an optimum condition on ammonia stoichiometry, discharge power, and gas flow rate; and (4) energy efficiency of NO_x reduction increases with increasing ammonia mixture and gas flow rate and decreases with increasing discharge power     

Energy Efficiency of Corona Discharge Reactor Driven by Inductive Energy Storage System Pulsed Power Generator

Characteristics of a pulse corona reactor driven by an inductive energy storage (IES) pulsed power generator are described in this paper with focusing on the influence of streamer-to-glow transition on NO removal efficiency. A pulsed high voltage with a short rise time of under 30 ns is employed to generate streamer discharges homogeneously in whole the discharge region. Fast recovery diodes are used as semiconductor opening switch (SOS) to shorten the rise time. The various resistors are employed as dummy load to clarify a suitable circuit parameter such as the capacitance of a primary energy storage capacitor and/or the inductance of a secondary energy storage inductor. The energy transfer efficiency of the pulsed power generator has a maximum value of 50% at 714 Omega dummy load resistance. A co-axial cylinder type discharge chamber was used as the corona discharge plasma reactor driven by the IES pulsed power generator. The pulsed power generator supplies 30 kV pulse with 300 pps repetition rate. The co-axial cylinder plasma reactor consists of 1 mm diameter tungsten wire and 19 mm i.d. copper tube with 30 cm length. NO removal from the simulated diesel engine exhaust gas (N₂:O₂=9:1, Initial NO concentration=200 ppm) increased with input energy into the reactor. The energy efficiency for NO removal was obtained to be 25 g/kWh at 30 % removal in gas flow rate of 2 L/min. However, the energy efficiency decreased to 5 g/kWh with increasing capacitance of the primary capacitor from several hundreds pF to several nF. This decrease was caused by a streamer-to-glow transition. The efficiency was affected by oxygen concentration in the gas mixture.     

大气压下同轴圆柱反应器DBD等效电路模型参数预测

大气压下同轴圆柱反应器介质阻挡放电在气体处理领域应用广泛。反应器等效电路模型是高性能介质阻挡放电电源设计的关键。然而,反应器等效电路模型参数随工作状况而非线性变化,这增加了复杂工况下系统精准设计的难度。针对这一问题,在非线性钳位等效模型的基础上采用遗传算法优化的神经网络对反应器等效模型参数进行预测。以系统的电压幅值、工作频率、气体流速和气体温度作为模型输入,以非线性钳位模型的钳位电压、介质等效电容和气隙等效电容作为模型输出。实验结果表明,在较宽的预测范围内,该方法保持较高的预测精度。利用该方法在全局范围内对反应器介质阻挡放电等效模型参数进行预测,可以为复杂工况下的电源设计提供更准确的反应器等效模型。     

Generation of a large area thermal induction plasma by applying a 50 kHz magnetic field

Inductively coupled radio frequency plasmas are gradually becoming an important source of high-temperature and high-reactivity plasmas for processing new functional materials or for removal of unwanted substances. Spatially wider plasmas are required for higher rate, more uniform processing in the future. Although low MHz frequencies have been usually used for induction plasmas, an attempt to expand the high temperature plasma fields was made by superimposing lower frequency 50-kHz magnetic fields on the DC plasma discharge to obtain a small source plasma. Because the penetration depth in such a low frequency field is as long as a few hundred mm, a larger radius plasma can be expected. As a first step, we have investigated the operating conditions under which a stable low frequency plasma is generated, based on theoretical calculations that include the time dependent rate equations for heat transfer and fluid flow in conjunction with the Maxwell electro-magnetic equations. Results showed that the minimum necessary power for expanding a small DC plasma to a wider plasma 100 mm in diameter by applying a 50-kHz magnetic field, is about 130 kW at 0. 1-MPa pressure. This power level is recognized to be within the available range in existing high-power oscillator systems. Measurements were carried out of the time variation of the spectral emission from the plasma immediately after superimposing the 50-kHz magnetic field upon a small area plasma generated with DC power of 1.5 kW at a pressure of 0.01 MPa in Ar gas. At a low power level of about 60 kW, the small plasma starts to expand in the radial direction, and finally, converges to a new wider plasma with 100 mm diameter. FFT analysis of the oscillograph showed that during the transient state, a period fluctuation in light emission occurs at a few tens of Hz reflecting the thermal time constant of a few tens of ms, besides the power frequency of 41.7 kHz. The plasma temperature was estimated by using the spectroscopic line intensities from neutral Ar atoms, as between 8,000 and 11,000 K. A uniformly distributed temperature field was successfully produced by applying the 50-kHz magnetic field, as expected. © 1998 Scripta Technica, Electr Eng Jpn, 123 (4): 48–57, 1998     

Atmospheric pressure discharge plasma decomposition for gaseous aircontaminants-trichlorotrifluoroethane and trichloroethylene

The decomposition performance of gaseous environmental destructive contaminants in air by using atmospheric pressure discharge plasma including the surface discharge induced plasma chemical processing (SPCP) was examined. The main contaminants tested were chlorofluorocarbon (CFC-113) and trichloroethylene, typically. The discharge exciting frequency range studied was wide-50 Hz to 50 kHz. Results showed the low frequency discharge requires high voltage to inject high electric power in the gas and to decompose the contaminants. A gas chromatograph mass spectrometer was used to analyze discharge products of dense CFC-113 or trichloroethylene. Among the detected products were HCl, CCIFO, and CHCl₃. Two different electrode configurations; the silent discharge (coaxial) electrode and the coil-electrode were also tested and compared to each other as a gas reactor     

滑动弧放电等离子体去除甲苯的实验研究

为了研究滑动弧放电等离子体对挥发性有机物的净化效果,选取甲苯作为代表物质进行实验研究,观察了电极间隔、电极材料、电极厚度、氧气含量、水汽含量、气流温度、污染物质量浓度等参数对去除率的影响。在输入体积能耗为0.26 kWh/m3、电极间隔为3 mm、电极厚4 mm、气体流量0.8 m3/h、甲苯质量浓度为7 850 mg/L的实验条件下,甲苯的去除率达到90%,反应器的能量利用率达到最大26.92 g/kWh;制作电极的金属材料对反应器的性能影响不大;甲苯去除率随着氧气含量、水汽含量和气流溫度的增加而增加,随着污染物浓度的增加而降低。     

Influence of voltage rise time on oxidation treatment of NO in simulated exhaust gas by polarity‐reversed pulse discharge

This paper describes an experimental study of NO removal from a simulated exhaust gas by repetitive surface discharge on a glass barrier subjected to polarity‐reversed voltage pulses. The very fast polarity‐reversal with a rise time of 20 ns is caused by direct grounding of a charged coaxial cable 10 m in length. The influence of the voltage rise time on energy efficiency for NO removal is studied. The results of NO removal using a barrier‐type plasma reactor with a screw‐plane electrode system indicate that the energy efficiency of very fast polarity reversal caused by direct grounding is higher than that of slower polarity reversal caused by grounding through an inductor at the cable end. The energy efficiency of direct grounding is approximately 80 g/kWh for a 50% NO removal ratio and approximately 60 g/kWh for a 100% NO removal ratio. Very intense discharge light is observed at an initial time of 10 ns for fast polarity reversal, whereas the intensity of the initial discharge light for slower polarity reversal is relatively small. To confirm the effectiveness of the polarity‐reversed pulse application, a comparison of the energy efficiency of polarity‐reversed voltage pulses and an AC 60‐Hz voltage is presented. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 32–38, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21215     

等离子体资源化模拟烟气脱硫的实验研究

针对目前传统烟气脱硫方法不能完全满足需要的情况,采用强电离放电的方法产生非平衡等离子体,进行了不外加吸收剂和催化剂的SO2脱除实验研究,该法在密闭的等离子体反应器中将SO2直接氧化为H2SO4,实现资源化脱硫且无二次污染。实验分别研究烟气的φ(H2O)、初始φ(SO2)、外加电压U、停留时间tr等因素对脱硫效率η的影响。结果表明,U=3.5 kV、气体流量Q=0.16 m3/h、φ(H2O)=2.1%t、r=0.85 s时,η可达80%。     

注入功率及耗能密度对离子输运率的影响

大气压非平衡等离子体的输运特性直接制约着工业电收尘和飞行器等离子体隐身的进一步发展,影响该输运特性的因素较多,包括放电区的压力、气体流速、电场强度、注入功率密度及其耗能密度等。为提高大气压非平衡等离子体输运效率,以线板形式电晕放电为手段进行电离流经放电区气体的实验,运用DLY-3型大气离子测量仪测量脱离电场约束的正负离子浓度,研究了注入功率密度及耗能密度对离子浓度输运率的影响。研究结果表明,在一定程度上随着注入功率密度、耗能密度的增加,离子浓度输运率越高.但当注入功率密度和耗能密度达到一定值时,离子输运率变化趋于平缓;同时,高风速比低风速的等离子体输运率要高出几个数量级。     

Surface-discharge characteristics in a ferrite-cathode diode

The surface-discharge characteristics of a HV diode with a planar ferrite cathode are described. This experimental setup consists of a constant HV power supply, a polarity inversion line pulser with a 200 m coaxial cable, a turbomolecular pump and a discharge chamber. The chamber was of a diode type which was evacuated by a turbomolecular pump with a pressure of 13.3×10^-3 Pa and was composed of a tungsten disk anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The cathode was set perpendicular to the anode plane, and the space between the anode and cathode electrodes had a value of 0.5 mm. The coaxial cable of the pulser was charged from 10 to 40 kV by the power supply, and the rectangular pulses with output voltages of -1× the charged voltage were produced with short rise times of ~20 ns. The effective duration of the pulse was determined by the cable length and had a value of ~1 μs. The process of the flashover investigated in this report consisted of two stages. In the first stage, because the discharge current flowed inside the cathode plate, the current was primarily regulated by the cathode impedance in proportion to the resistance. Next, the current substantially increased with corresponding growth of the surface discharge on the ferrite cathode. The duration of the initial current increased with the thickness of the cathode and the diameter of the contact electrode. In the present work, the maximum current was determined by the characteristic impedance of the pulser cable since the discharge impedance in the diode substantially decreased during the surface discharge     

The C2H2 gas effect on the growth behavior of remote plasma enhanced CVD SiC:H film

SiC:H films were produced in a remote plasma enhanced chemical vapor deposition (RPE-CVD) system. The HMDS was chosen as the primary source gas and was fixed at constant flow rate of 10 sccm. The C₂H₂ gas input amount was varied from 3 to 200 sccm for the study of carbon effect on the film stoichiometry and bonding properties. The deposition temperature of the substrate was fixed at 400^∘C, and the plasma power was fixed at 300 W. Using auger electron spectroscopy, the depth profile of the film was investigated with C₂H₂ flow rate changes. The C₂H₂ played an important role in the transition between sp² and sp³ carbon hybridization bonds, which affected the growth behavior and properties of the films.     

二维交流滑动弧放电物理参数分析

笔者对刀片式交流滑动弧放电过程进行了系统的分析,考察了进气流量、电极间距等因素对放电电压、电流、放电功率、对流换热等物理参数的影响.实验结果表明:当流量较低,如0.9 L/min时,放电电压随着弧长增加呈现二次曲线增长;当流量提高,超过10 L/min时,放电电压在电弧较短区域变得紊乱.放电功率随着气流量的增加.先线性...     

Regeneration of Honeycomb Zeolite by Nonthermal Plasma Desorption of Toluene

In order to develop an economical volatile organic compound (VOC) removal process, a concentration technique using nonthermal plasma combined with an adsorption process is investigated. Toluene—one of the most commonly used VOCs—is used, and the optimization of plasma desorption is investigated. The effects of toluene concentration and adsorbent regeneration are investigated by varying the plasma desorption methods: closing method, in which a carrier gas is stopped flowing during a portion of plasma desorption time, and nonclosing method. As a result, the closing method is favored with regard to parameters such as concentration, desorption efficiency, regeneration efficiency, and by-product formation. Then, the plasma desorption using closing method is investigated as a function of discharge power, closing time, a carrier gas flow rate for plasma desorption, and plasma desorption time. When a 2-L/min and 30-ppm toluene gas is employed as a target gas, a toluene concentration exceeding 30 times the original concentration is achieved with a reduction in the gas volume by 1/60. The repeatability of adsorption and plasma desorption is successfully demonstrated; these processes yield an extremely effective and practical VOC removal process.      

Numerical Simulation of Power Generation Characteristics of a Disk MHD Generator with High‐Temperature Inert Gas Plasma

The power generation characteristics of a disk magnetohydrodynamics (MHD) generator with high‐temperature inert gas (argon) plasma have been examined by a time‐dependent two‐dimensional numerical simulation. The numerical simulation results based on the experimental conditions show that the enthalpy extraction ratio (= electrical output power/thermal input) can reach above 10%, which surely supports the reasonability of the experimental results. Proper selection of working conditions, especially the inlet total gas temperature, is necessary, since the gas temperature dominantly determines the electrical conductivity in the generator, unlike the conventional seeded plasma MHD generator. It is also found that the plasma is not in the recombination process but in the ionization process, where the ionization degree moderately increases along the flow. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 23–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21237     

利用非平衡等离子体方法将CO2还原成CO的研究

CO2和H2合成CO是CO2化学利用的重要过程,然而,传统的催化转化难以实现高效转化。在室温和大气压下,通过非平衡等离子体对H2和CO2的活化作用,考察了等离子体反应器结构、极间距、放电功率和氢碳比等对CO2转化率、CO选择性和CO2转化的能量效率影响。实验结果表明,在室温和大气压下,用等离子体法可将CO2高效的还原为CO,适当调节上述各参数可提高CO2的转化率。采用管管式等离子体反应器,在放电频率为10kHz、H2与CO2体积进料比为2:1、放电功率为80W、CO2气体体积流量为120mL/min的条件下,CO2转化率为88.2%,CO选择性为100%。