Indoor air cleaning using a pulsed discharge plasma

The purpose of this paper is to develop a high-efficiency air-cleaning system for air pollutants such as tobacco smoke found in indoor environments. The authors investigated the basic characteristics of treating particulate matter and acetaldehyde (CH₃CHO) in a one-pass test using a pulse generator and a plasma-driven catalyst reactor, both of which are attachable to an air conditioner. Using a circulation test, the decrease in acetaldehyde concentration was measured in a closed vessel where the reactor had been placed. The removal efficiencies of particulate matter and acetaldehyde in the one-pass test (residence time of 10 ms) were 70% and 27%, respectively. In the circulation test, 98% of the suspended particles were collected after 2 min of operation and the acetaldehyde concentration decreased by 70% after 50 mins. It is believed that the TiO₂ catalyst is excited by plasma-induced high-energy particles (electrons, photons, and metastable molecules), resulting in an enhanced pollutant removal. These test results indicate that the combination of plasma with TiO₂ is a potential alternative in treating the pollutants in environmental tobacco smoke     

NOx removal process using pulsed discharge plasma

Nonequilibrium plasma can be used to promote chemical reactions that reduce the emission of gaseous pollutants, such as NO_x, produced by coal-burning power plants or by diesel engines. Laboratory experiments were carried out to study the decrease of NO_x in simulated flue gases (initial concentration of NO: 200-800 ppm, O₂ : 10%, N₂-balance gas) by means of a pulsed discharge plasma generated in a cylinder type reactor (outer electrode: 20-mm diameter). A rotating spark gap provided square wave high-voltages up to 25-kV, at a frequency of 250 Hz, to corona electrodes of 0.1-, 3.3-, and 6.4-mm diameter. The tests were performed at various temperatures (ambient to 220°C) and constant residence time (0.6 s). The removal performance depended on the size of the discharge electrode and was better at room temperature. The addition of C₂H₄ significantly enhanced the removal performance, concentration of NO_x decreased from 800 ppm to 300 ppm in the discharge. The by-products of this process were analyzed using infrared spectroscopy. No traces of toxic gases could be detected     

Generation of cabbage-shaped nanocarbons using arc discharge in a foam

Nanocarbons with a cross-section in the shape of a cabbage were generated using an arc discharge in foam, which represents a gas-fluid multiphase. TEM observations indicated that these cabbage-shaped nanocarbons have a diameter of 50-500nm and represent spherical materials resembling the shape of a twisted graphite sheet. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Radiation characteristics as a function of the gas flow rate emitted from argon torch plasma arc discharge

When a reduction of the waste and dissolution of the iron are carried out by means of an arc plasma, the radiant power of the arc should be suppressed. In those cases the radiant power from the plasmas has to be precisely controlled. Therefore, we tried to measure the radian power from the torch plasma using a power meter. The radiant power was measured to be about 620 to 950 W for an external plasma length of 2 cm at a current of 100 A, with gas flow rates of 4 to 20 l/min (Normal), and increases in proportion to the 0.25 to 0.37 power of the gas flow rate and with the increment of external plasma length and the plasma current. The total radiant efficiency is 32 to 40% in the condition mentioned above in the sphere model. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 1–8, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10006     

Low-temperature soot incineration of diesel particulate filter using remote nonthermal plasma induced by a pulsed barrier discharge

Regulations regarding automotive diesel engine emissions become more severe every year, and it is difficult to meet the requirements with only combustion improvement techniques. More effective post-processing technology is desired especially for particulate matter (PM), such as carbon soots. Although the use of a ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists for the soot removal or regeneration at low temperature, especially at cold start and engine brake operation. In the present study, a regeneration of a DPF is investigated using indirect or remote nonthermal plasma (NTP) method. The NTP-treated air is injected into exhaust gas, and the NO is oxidized to NO/sub 2/. The induced NO/sub 2/ and activated oxygen species are used to incinerate carbon soot deposited on the DPF. It is confirmed experimentally that the pressure drop decreases when the plasma is turned on and the regeneration of the DPF is possible at the low temperature of 300/spl deg/C. The specific energy density is 22 Wh/m/sup 3/ (= 78 J/L). Although the condition of the NTP is not optimized in the present study, further improvement is required in the energy efficiency.     

Theoretical studies on nanosecond surface discharge phenomena observed using Lichtenberg figure method

Contents The nanosecond surface discharge phenomena on the insulation plate have been studied using a Lichtenberg figure method. In the experimental setup voltages of +7 to 22kV, pressures of 150–760 Torr and pulse widths of 3–11 nsec were applied. The developing length of the positive corona streamer has been precisely measured against the applied voltage as a function of the pressure at a given pulse width.It was found that with increasing pressure there was an increase of inception voltage, while the time lag of corona streamer inception decreased. The developing velocity of charged particles on the insulation plate is discussed from a view point of a modified drift theory of charged particles. Finally, it is concluded that the detardation factor due to the photoelectric emission from the insulation plate plays a more important role in the corona streamer development than the electron collision ionization or the gas photoionization.

---

Theoretische Untersuchung von Gleitentladungen im Nano-Sekunden-Zeitbereich mit der Methode der Lichtenbergschen Figuren

Übersicht Es wurden Gleitentladungen auf Isolierstoffoberflächen im Nano-Sekunden-Zeitbereich mit der Methode der Lichtenbergschen Figuren untersucht. Experimentell wurden Spannungen von +7 bis 22 kV, Impulsbreiten von 3 bis 11 ns und Gasdrücke über dem Isolator von 150 bis 760 Torr angewendet. Die Elektrodenanordnung bestand aus einer Nadel und einer ebenen Elektrode, die mit der Isolierstoffplatte bedeckt war. Die Ausbreitungslänge der positiven Koronaentladung wurde als Funktion der Spannung bei verschiedenen Drücken und konstanter Impulsbreite gemessen.Es zeigt sich, daß sich bei zunehmendem Druck die Einsatzspannung der Koronaentladung erhöht, während sich die Verzögerungszeit vermindert. Die Ausbreitungsgeschwindigkeit der Koronaentladung auf der Isolierstoffoberfläche wird unter dem Gesichtspunkt einer modifizierten Theorie der Ladungsträgerbeweglichkeit auf der Oberfläche diskutiert. Bezüglich der Ausbreitung der Koronaentladung auf der Isolierstoffoberfläche zeigt ich, daß offensichtlich die Photoelektronenemission von der Oberfläche einen größeren Einfluß hat als Elektronenstöße und Photoionisation im Gasraum über dem Isolierstoff.

     

Portable space charge measurement system using the pulsed electrostatic method

The pulsed electroacoustic (PEA) method is used to measure space charge distributions in insulating materials. A high-resolution PEA measurement system and signal procedure has been discussed in previous papers. Since the signal procedure is necessary for high-resolution measurement, the system must include a computer. In this paper, a new PEA system without signal processing is introduced. In order to eliminate the inevitable signal distortion of the conventional PEA method, the new system employs a new voltage waveform generator, one that is different from the very narrow pulse generator used in conventional PEA systems. Using the new waveform, designed based on the impulse response of the measurement system; the output signal can show the space charge distribution directly, without the need to conduct deconvolution. Thus, space charge distributions can be measured on site, such as in a factory, with a portable oscilloscope. The spatial resolution of the space charge measurement of the system is 10 /spl mu/m, which is the same as that of conventional PEA systems. Such a portable PEA system can contribute to various industrial applications.     

Wide-range two-dimensional imaging of NO density profiles by LIF technique in a corona radical shower Reactor

Planar laser-induced fluorescence was employed during the process of NO/sub x/ removal in a corona radical shower system. Using the wide-range imaging (image size: 240 mm in width and 160 mm in height), two-dimensional distributions of ground-state NO could be observed not only in the discharge zone but also both in the downstream and the upstream regions of the reactor. The obtained results showed that the density of NO molecules decreased not only in the plasma region formed by the corona streamers and the downstream region of the reactor but also in the upstream region of the reactor. The effect of the gas injection through the nozzles electrode on the NO profile in the reactor was negligible. The NO removal rate was almost the same for both cases with and without the injection gas once the streamer discharge was produced. In the present reactor at low main gas flow rate, it was considered that electrohydrodynamic flow became to be dominant, and the flow toward the upstream affected the decrease of NO in the upstream region. This fact is important for optimizing the performance of the nonthermal plasma reactor.     

水中交流电弧伏安特性仿真

为了在流动的水中产生交流电弧对废水进行处理,设计了实验系统及测试电路,建立了适合水中交流电弧的动态模型.将经典的Mayr和Cassie电弧微分方程模型以串联电阻的方式联合起来,针对水介质的特点引入了最小电导参数,确立了模型参数的求解方法.并将电弧数学模型转化为电路模型,对电弧的动态伏安特性进行了仿真.仿真结果表明:实测与仿真的电弧电压、电流波形基本一致;水中交流电弧放电过程存在气液两相放电,但稳定的电弧放电实质上发生在水蒸气中;稳定燃弧电压为100 V, 电流自然过零时存在1～2 ms的熄弧时间;熄弧时段内,电流接近于零并且变化缓慢,电压则迅速升至约1 500 V使电弧重燃.     

Characterization of nanostructured Fe/C multilayers by a pulsed cathodic arc

Nano-multilayer have been deposited by a pulsed cathodic arc deposition with varying thicknesses of each layer less than 2 nm and examined by cross-sectional transmission electron microscopy (XTEM). Computer simulations are performed to get a better understanding of the deposition of nano-multilayer during deposition and compared with the XTEM results.     

Portable application of thermal plasma and arc discharge for waste treatment,thermal spraying and surface treatment

Thermal plasma and arc discharge have numerous useful characteristics related to their high temperature and intense radiation. Many applications have been developed. Recently, a portable twin‐torch plasma arc furnace for waste treatment, thermal spraying torches, steam plasma torches, and surface treatment of low‐pressure arc was developed. This paper describes the recent development of a portable application of thermal plasma and arc discharge. The portable device can treat wastes and perform thermal spraying and surface treatments on site. This technology is expected to become more attractive. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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.     

脉冲激光测距中电子精密测量

本文阐述恒比定时触发器及计时内插扩展技术在脉冲激光测距中,测量精度的提高及误差分析.     

Thermionic arc breakdown in small discharge gaps: model andapplications

A model for thermionically induced breakdown is developed which predicts the voltage levels experienced in low-voltage discharges. Initially, electron emission across an active discharge minigap must be established. Prior to breakdown, emitted electrons populate the cathode space-charge region and the remaining gap is unionized. Breakdown criteria and a means for estimating the reduced breakdown voltage in the bulk gas are derived in terms of conventional Townsend ionization mechanisms, wherein multistep or cumulative ionization must be active. Since the cathode space-charge region is replete with emitted electrons, positive ions traversing it release to the bulk gas considerably more electrons than would be available with the conventional Townsend γ mechanism at the cathode surface. This equivalently higher γ significantly shifts the Paschen curve toward lower minima. One practical thermionic assisting device is a tungsten light-bulb-grade filament, which shunts the primary discharge electrodes and, within the filament's minigaps, breakdown occurs. Thermionic arc breakdown has been implemented in the starting of arc devices for lamps and in thermionic power converters; an application to ionization chambers in electrostatic thrusters is also discussed     

Basic study on calibration using waveform variation in space charge measurement by pulsed electroacoustic method

The pulsed electroacoustic method determines the distribution of space charge in an insulation system by applying a pulse voltage and detecting the acoustic response. It estimates the location and magnitude of charges from time-domain signals. For quantitative analysis, a bias voltage is applied to a specimen with no space charge, and the acoustic signal generated from the electrodes only is used as a reference waveform for calibration. However, a full-scale, extra-high voltage insulation system often already contains space charges in it. Therefore, a method of acquiring a reference signal under such a condition was studied. We studied methods to compare voltage variations and response signal variations. We proposed a method that measures the signal difference at different voltages. In addition, we proposed a method of correlating voltage and signal variations that may allo for more rapid signal acquisition. The feasibility was proved using an 11 mm-thick mimic polyethylene specimen.     

Development of partial discharge measurement method for pre-mold cable accessories with separated-shielding layers

Most of the accidents on XLPE cable line are caused by defective construction of cable accessories. Thus the authors developed a method to measure partial discharges in pre-mold cable accessories. The authors provided separated-shielding layers as detection electrodes in accessories, and discriminate between partial discharge pulse and noise pulse using realtime comparison of pulse current magnitudes from both detection electrodes. This paper describes the principle of the noise discrimination method, portable partial discharge measurement apparatus, and the results of field test.     

A pulsed corona-Townsend method for measurement of electron/ionnumber ratios and drift velocities

A new, easily-implemented method based on the pulsed-Townsend technique has been developed to measure drift velocities of charge carriers in a corona discharge at atmospheric pressure. The method also yields the electron/ion number ratio and an upper limit on the value of the electron attachment coefficient. Approximate electron drift velocities measured in nitrogen are in agreement with known values. In addition, the negative ion mobility obtained in nitrogen containing small amounts (0-3.7%) of oxygen agrees with known data. Therefore the pulsed corona-Townsend technique can be used to obtain data in gas mixtures of practical interest. The method can also distinguish the charge carriers in a corona discharge. This is especially useful in nonelectronegative gases with unknown concentrations of electronegative impurities     

谐振接地系统对地电容与消弧线圈电感统一测量方法

配电网对地电容的准确测量有助于保证消弧线圈的补偿效果,降低故障对配电网的损害。提出一种基于信号注入法与快速傅里叶变换的谐振接地系统对地电容与消弧线圈电感统一测量方法。首先建立中性点电压与系统对地电容、消弧线圈电感关系。其次向中性点接入非工频电流源,利用快速傅里叶变换得到中性点电压关于电流源频率分量,消除工频误差。然后根据等效电路实现系统对地电容与消弧线圈电感的统一测量。最后通过Simulink搭建仿真模型进行分析。结果表明,该方法适用于消弧线圈直接接地、消弧线圈并联电阻接地和串联电阻接地运行方式。三相不对称条件下,对地电容与消弧线圈电感最大误差分别为011%和01%;三相对称条件下,最大误差分别为13%和18%。     

Temperature rise in a birefringent substrate caused by RF discharge plasma

Temperature rises of a birefringent substrate (LiNbO₃) have been measured in an argon RF discharge plasma. The measurement method is based on monitoring the variation of natural birefringence with temperature by laser interferometry. Using this method, the dependence of substrate temperature rise on applied RF power and gas pressure has been investigated. The evaluation of the temperature curves shows that heat flux from the plasma toward the substrate is independent of time and temperature. The magnitude of the flux differs largely from the applied power, and is approximately 0.4% of the power. By measuring the electron density, electron temperature, and plasma potential with a Langmuir probe, the energy of the ions incident on the substrate is estimated. The ion flux toward the substrate is calculated from the energy of ions and is compared with the measured heat flux. The dependence on the applied power is in approximate agreement between those fluxes. The temperature distribution over the substrate thickness is simulated numerically using the finite difference method. © 1999 Scripta Technica, Electr Eng Jpn, 127(4): 9–17, 1999     

Formation of chemical species and their effects on microorganismsusing a pulsed high-voltage discharge in water

The primary mechanism for sterilization of microorganisms by high-voltage pulses has been considered to be an electrical breakdown of the cell membrane. However, it is expected that many kinds of chemically active species would be generated by an electrical discharge in a needle-plate or rod-rod electrode system. Therefore it is necessary to identify the chemical species produced by the discharge and to investigate lethal effects of the active species on microorganisms. In the present study, the formation of active species in water (without O ₂ flow) and their effects on yeast cells were investigated using needle-plate electrodes. In the presence of the streamer discharge, H and OH radicals were detected by means of emission spectroscopic analysis of the discharge light. Hydrogen peroxide (H₂O₂) was also detected by absorption spectrophotometry using a reaction of peroxidase and catalase. The effect of the electrical conductivity of the water on the formation of the active species was investigated. Maximum ·OH and H₂O₂ concentrations were obtained at a water conductivity of about 10^-5 S/cm. The H₂O₂ formation mechanism was considered to be a recombination reaction of ·OH. The lethal effects on beer yeast of ·OH and H₂O₂ generated by the pulsed electrical discharge in water were also investigated. It was found that ·OH had almost no effect in reducing the survivors. However, the H₂H₂ did kill the yeast cells: the logarithm of the survival ratio decreased linearly with increasing H₂O₂ concentration