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     

空气源高频圆管型DBD臭氧产生的实验研究

电源频率和放电管长度是介质阻挡放电(DBD)臭氧产生的两个重要影响因素,在前期的研究基础上,采用合适的放电管长度和电源频率进行实验研究。实验研究了干空气源放电管长度、放电电压和气体流量对臭氧产生的影响,并进行了系统优化。研究结果表明:放电管长度由500 mm变为200 mm,在几乎不降低臭氧浓度下放电平均功率约降低了60%;臭氧浓度随放电电压和气体流量的增大先增大后降低;当流量为200 L/h、放电电压为2 698 V时,臭氧浓度与臭氧产率同时达到相对较高值,此时,臭氧浓度为5.3 g/m3时,臭氧产率为43.62 g/kWh。     

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     

Phenomenon of skipping sparks in discharges on a dielectric surface

Gliding sparks are associated with channel breakdown in air near a corona precharged dielectric layer backed by ground. Characterized by high current, their bright channels usually end in sudden branching/dimming. Infrequently, there occur cases in which channel brightness is interrupted, with no evident local branching but a new leader continuing on propagating after momentary delay. This skipping-spark phenomenon has been studied in an experimental system intended for taking Kirlian photographs. Operated in a Lichtenberg-figure mode, the method yields evidence in some detail. The authors report on observations of spark-channel touchdown and subsequent rebounding. A model based on nonuniform surface charging is proposed for explanation     

Ozone production in electrostatic air cleaners with contaminatedelectrodes

Runaway ozone generation due to contamination of electrode surfaces is a limiting factor in the long-term effectiveness of electrostatic air cleaners. Modification of the form of the corona discharge, accompanied by a significant rise in current, is the cause of increased ozone levels. After one week of operation in filtered air containing Arizona Road Dust, ozone concentration in a laboratory air cleaner increases by 460%. In this case, there is slight contamination on the discharge wires, but the ozone increase is attributed exclusively to back corona on the collection plates. On the other hand, oxidized discharge wires are believed to contribute to an order of magnitude increase in ozone concentration in a commercial air cleaner, operated in room air for 7 weeks. Wire contamination alone can increase ozone generation. An insulating tape adhesive applied to a 0.254 mm diameter stainless steel wire causes a 10-fold increase in ozone concentration     

Partial discharges in a polyimide taped air impregnated cable

Tests are performed, in a radiation free environment, to assess the partial discharge performance of cable for future use in a radioactive environment. The cable consists of layers of Kapton H tape wrapped around the conductor and with air as the impregnant. Considerable conditioning of the discharge sites was observed with a prolonged application at the higher voltage. Overall the performance of the cable appears to be satisfactory but further tests are required in the radioactive environment as this would tend to increase the discharge.     

Estimation of charge distribution on a bulky solid dielectric using regularization technique

We have been studying a multi‐point charge measurement method using an electrostatic probe. In this technique, charge densities x must be estimated from the probe outputs b by an inverse calculation based on an equation A x = b . The matrix A is obtained by applying a numerical field calculation technique. When the matrix A is in ill‐condition, the solution often makes no sense, including extremely large errors. Therefore, we apply the regularized least squares method (RLS) with a penalty term to perform the inverse calculation stably for the ill‐conditioned matrix. The penalty term imposes some constraints on the solutions. In this paper, first, we have analyzed the accuracy of the charge distribution estimated by the inverse calculation. Although the perturbation bound of the solution errors has already been proposed for the least squares method, it has not yet been given for the RLS. We have derived the equations that express the perturbation bound of the solution errors in applying the RLS to evaluate the estimation accuracy. Second, we have applied the above equations to an experimental result for a cylindrical dielectric solid, and estimated the charge distribution represented by 10,140 unknowns. We have utilized an iteration technique and the symmetric configuration of the measured arrangement so as to reduce the amount of operations and memory capacity required for the inverse calculation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 1–13, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20412     

Fast electrostatic discharges between a charged thin dielectricfilm and a spherical electrode with or without dielectric coating

Short-gap (less than 1 mm) electrostatic discharge (ESD) between a charged thin dielectric film on an earthed-plate electrode and a spherical electrode, connected to the plate, with or without an uncharged thin dielectric film coating was observed. Discharge-current waveform, discharge gap length, current rise time, discharging photograph, and current peak value were recorded by the authors' measuring system. The initial charge supply effects by irradiation of β-ray or ultraviolet light were found to be not highly apparent; that is, the reproducibility of ESD experiments was not greatly improved. Surface-charge-polarity dependence of surface ESD between charged and uncharged dielectric films decreases with increase of the film thickness. The discharge gap length of ESD with a 1.5 μm uncharged film coating on the spherical electrode decrease to 50 or 70% compared with that between a charged film and a bare spherical metal electrode. Peak current and transferred charge value of ESD also decrease to roughly one-third of that between the film and the spherical electrode     

Development of a laser wavefront sensor for measurement of discharges in air

A laser wavefront sensor of the Shack‐Hartmann type capable of simultaneous measurement at two wavelengths was constructed. The sensor uses a single optical path, and is suited for applications such as high‐voltage discharges in air, in which large insulation distances are necessary. The sensor was used to detect optical path differences due to an impulse discharge in air across a needle–plane electrode gap of gap length 17 mm. Optical path differences were measured at laser wavelengths of 532 and 1064 nm at 1.6 µs after insulation breakdown across the gap. From the difference in optical path differences at the two wavelengths, a line‐integrated electron density distribution in the direction perpendicular to the gap was obtained near the high‐voltage electrode. The distribution had a peak value of 1.4 × 10²⁰m^?2 and a full width at half maximum of 4.4 mm. Because of the coverage of a large observation area including the entire gap, the spatial resolution was 1.4 mm, which was inadequate to obtain the precise form of the electron density distribution. However, the results show the possibility of applying laser wavefront sensing to electron density measurement. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 10–17, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10247     

Comparisons of direct-current breakdown characteristics in dry air and SF6 gaps using a parallel-plane arrangement with variable height protrusion

Breakdown voltages in uniform and quasi-uniform field gaps are sensitive to the presence of small protrusion on the electrode surface in SF₆ at high pressures. The aim of the present work is to study direct breakdown and corona stabilized breakdown for the transitive region from uniform to nonuniform gap in dry air and SF₆ at low pressures up to a critical pressure when direct breakdown takes place by a leader discharge crossing the gap in SF₆. In a parallel-plane gap with a variable-height protrusion subjected to the dc voltage, corona onset voltage is remarkably controlled by the protrusion height. The present electrode arrangement has the advantage of directly measuring the minimum critical guiding field strength for the propagation of a streamer discharge at corona onset. The experimental observations have been explained qualitatively on the basis of a streamer model and precise electric field calculations of gap.     

Sterilization of E. coli by underwater pulsed streamer discharges in a continuous flow system

Underwater pulsed streamer discharges using a wire‐to‐cylinder electrode contained in a 42‐mm‐diameter glass tube were investigated with respect to its spatial spread associated with voltage waveforms. A discharge reactor with a continuous flow system was employed to sterilize E. coli suspended in saline water (10 mS/m). The discharge electrode consisted of a 0.1‐mm‐diameter metal wire for the high voltage and a mesh cylinder for the ground electrode. Tens of disk‐shaped discharges emerged from the wire electrode and propagated toward the cylinder as long as the voltage lasted. The spatial expanse of the discharge was proportional to the cube of the pulse duration and to the amplitude of the voltage. The sterilization experiment showed that the survival ratio of bacteria over discharges was proportional to the average number of the exposures to the discharges while in the reactor. The minimum ratio of surviving bacteria was only 15% under 130 exposures, which corresponds to an energy expenditure of 35 J/ml. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 1–7, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20554     

Effects of frequency, temperature, compression, and air pressure onthe dielectric properties of a multilayer stack of dry kraft paper

Kraft paper is used extensively in the electricity supply industry for the insulation of HV apparatus, such as transformers, capacitors and cables. Because of the fibrous nature of the paper, many layers are stacked or rolled to obtain the required electric strength. The insulation is thus a combination of cellulose and an impregnating fluid, which may be a liquid, a gas or vacuum. The dielectric properties of such a system depend on the dryness, temperature, frequency and the degree of mechanical compression. Although the effects of moisture, temperature and frequency on the dielectric properties of kraft paper have been studied, very little work has been done on the effect of compressive stress, particularly long-term effects. Results are presented of measurements, in the frequency range 50 Hz to 20 kHz, of the effects of compressive stress and temperature on the real and imaginary parts of the complex relative permittivity of a multilayer stack of dry kraft paper under vacuum. The variations of the dc resistance with compressive stress and temperature also are reported. Results are given of the variation of the dielectric properties of a stack of paper following a step change in either the temperature or the air pressure. The long-term variations are attributed to the slow diffusion of ions through the stack, particularly those held at the interfaces between layers     

Partial discharge measurements in air and argon at low pressures with and without a dielectric barrier

Partial discharge (PD) characteristics in air and argon under low pressures down to 13.3 Pa (0,1 Torr) and 60 Hz AC energization are studied in an energized needle-plane electrode arrangement. The electrode configuration, vacuum chamber, facilities, and electrical connections for the experimental setup are described. Two cases are studied for each of two gases, air and argon, with 20 mm spacing between the two electrodes: (1) with and (2) without a Teflon/spl reg/ cap (dielectric barrier). Results for the four series of experiments and analysis of the discharge current pulse waveforms are presented. Topics discussed are the typical waveforms of the discharge current pulses at different pressures, and discharge current pulse rise time vs. pressure relationships.     

Combined carbon‐dioxide‐capturing high‐performance power generation system using a solid oxide fuel cell operating on pressurized fuel/air

The authors recently proposed a high‐performance combined carbon‐dioxide‐capturing power generation system using a solid oxide fuel cell (SOFC) and a closed‐cycle MHD generator, in which pure oxygen is used as the oxidant. This combined system makes the best use of the advantages of combustion with pure oxygen but fails to prevent the efficiency deterioration caused by high power demand for oxygen production. In the present study, the authors modified this previous system and proposed an improved combined carbon‐dioxide‐capturing power generation system using SOFC/MHD characterized by a higher overall thermal efficiency. In this system, pure oxygen is supplied only to the combustor to reduce the power required for the oxygen production, and pressurized air is used as the oxidant gas in the SOFC. The power saving amounts to about 5% of the thermal input, resulting in a very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value of the overall thermal efficiency of carbon‐dioxide‐capturing systems. Advantages of the proposed system suggest that it is advisable to continue further research in this direction. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 21–30, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20010     

基于脉冲漏磁的带保温层管道腐蚀缺陷检测

在带保温层金属管道腐蚀检测方面,脉冲漏磁技术显示了潜在的优势.利用有限元分析软件Comsol Multiphysics对不同结构的传感器进行仿真分析的基础上,提出了一种优化结构的脉冲漏磁传感器,用于带保温层的管道腐蚀缺陷的检测.通过实验验证了传感器结构优化设计的有效性,为进一步量化分析缺陷信息打下基础.     

Modeling the superconducting effects on resonance and radiation characteristics of a cylindrical-rectangular microstrip antenna covered with a dielectric layer

In this work, the resonance and radiation characteristics of a superconducting cylindrical-rectangular microstrip antenna covered with a dielectric layer are studied using an electric field integral equation and the spectral-domain Green’s function. The effect of superconductivity of the patch is modeled by including surface complex impedance in the formulation. In order to validate the present method, numerical results for the cylindrical microstrip antenna with a perfectly conducting patch are presented and very good agreement has been demonstrated between our computed data and those found in the literature. Once the validity of the method is checked, the effect of the superconducting patch on resonance frequency, half-power bandwidth and radiation pattern of cylindrical rectangular microstrip patch is studied. It is found that the resonant frequency is affected significantly by the superconductivity property of the patch and the half-power bandwidth is considerably increased, which improves the narrow bandwidth characteristics of the microstrip structure. Further results show that a thin superconductor patch has a significant effect on the E-plane radiation pattern.     

Gas dynamic and force effects of a solid particle in a shock wave in air

Shock wave interaction with an adiabatic solid microparticle is numerically simulated. In the simulation, the shock wave is initiated by the Riemann problem with instantaneous removal of a diaphragm between the high- and low-pressure chambers. The calculation is performed in the two-dimensional formulation using the ideal gas equation of state. The left end of the tube is impermeable, while outflow from the right end is permitted. The particle is assumed to be motionless, impermeable, and adiabatic, and the simulation is performed for time intervals shorted than the time of velocity and temperature relaxation of the particle. The numerical grid is chosen for each particle size to ensure convergence. For each particle size, the calculated hydraulic resistance coefficient describing the particle force impact on the flow is compared with that obtained from the analytical Stokes formula. It is discovered that the Stokes formula can be used for calculation of hydraulic resistance of a motionless particle in a shock wave flow. The influence of the particle diameter on the flow perturbation behind the shock front is studied. Specific heating of the flow in front of the particle is calculated and a simple estimate is proposed. The whole heated region is divided by the acoustic line into the subsonic and supersonic regions. It is demonstrated that the main heat generated by the particle in the flow is concentrated in the subsonic region. The calculations are performed using two different 2D hydro codes. The energy release in the flow induced by the particle is compared with the maximum possible heating at complete termination of the flow. The results can be used for estimating the possibility of gas ignition in front of the particle by a shock wave whose amplitude is insufficient for initiating detonation in the absence of a particle.     

Thermodynamic substantiation of power generation using a steam-gas mixture with a variable composition of components

In incomplete conditions of initial information for the calculation of thermodynamic parameters of the steam-gas cycle, the ideal gas approximation is accepted. In order to increase the efficiency of using the energy of the steam-gas flow, the possibility of using a binary thermal power cycle is considered.     

Breakdown of air over a water surface stressed by a perpendicularalternating electric field, in the presence of a dielectric barrier

Distortion of the surface of a water layer serving as the ground electrode of an experimental ozone generator has a strong influence on the generator's performance. The distortion is highly affected by the frequency, as well as the magnitude, of the applied electric field. In turn, the resultant field is affected by the distortion. Over the frequency range tested (20-300 Hz), the applied field required to initiate electrical breakdown of the air over the water surface was found to be less than that required for breakdown over a flat metallic electrode. This reduction in applied field for breakdown is attributed to a reduction of the air-gap height due to an upward bulge of the water surface, and to field intensification by sharply pointed cones. The cones are most predominant at lower frequencies