Effect of toughened epoxy resin on partial discharge at solid-solid interface

A series of solid-solid interfaces,consisting of ceramic-epoxy resin interface samples with a tip-plate electrode,were investigated by performing partial discharge tests and realtime electrical tree observations.A toughening agent was added to the epoxy resin at different ratios for comparison.The impact strength,differential scanning calorimetry(DSC) and dielectric properties of the cured compositions and ceramic were tested.The electric field strength at the tip was calculated based on Maxwell's theory.The test results show that the addition of a toughener can improve the impact strength of epoxy resin but it decreases the partial discharge inception voltage(PDIV) of the interface sample.At the same time,toughening leads to complex branches of the electrical tree.The simulation result suggests that this reduction of the PDIV cannot be explained by a change of permittivity due to the addition of a toughening agent.The microstructural change caused by toughening was considered to be the key factor for lower PDIV and complex electrical tree branches.     

Effects of packing particles on the partial discharge behavior and the electrical characterization of oxygen PBRs

Packed-bed reactors(PBRs) hold great promise for environmental applications, but a deeper understanding of the behavior of plasma discharge within PBRs is required. To this end, a partial-discharge alternative equivalent circuit for PBRs was established in this work. Dielectric particles(glass beads or glass sand) were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs. Some electrical characterizations were explored(e.g. the effective dielectric capacitance, partial discharge coefficient, and corrected burning voltage) that may differ from long-standing interpretations.The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size. For partial discharge, the effective dielectric capacitance is always less than the dielectric capacitance. The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size. As compared to an empty reactor, the average electric field in the PBR was found to be improved by 3–4 times, and the ozone energy efficiency and production were promoted by more than 20% and 15%,respectively. The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex, irregularly-shaped packing material that is suitable for the discharge gap.     

Influence of high-voltage pulse parameters on the propagation of a plasma synthetic jet

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s⁻¹ and 100 m s⁻¹, respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s⁻¹ to 93 m s⁻¹. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG- 18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s⁻¹ is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s⁻¹ is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.     

Atmospheric air dielectric barrier discharge excited by nanosecond pulse and AC used for improving the hydrophilicity of aramid fibers

In this paper, a long line-shape dielectric barrier discharge excited by a nanosecond pulse and AC is generated in atmospheric air for the purpose of discussing the uniformity, stability and ability of aramid fiber treatment. The discharge images, waveforms of current and voltage,optical emission spectra, and gas temperatures of both discharges are compared. It is found that nanosecond pulsed discharge has a more uniform discharge morphology, higher energy efficiency and lower gas temperature, which indicates that nanosecond pulsed discharge is more suitable for surface modification. To reduce the water contact angle from 96° to about 60°, the energy cost is only about 1/7 compared with AC discharge. Scanning electron microscopy,Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy are employed to understand the mechanisms of hydrophilicity improvement.     

Investigation on the Micro-Discharge Characteristics of Dielectric Barrier Discharge in a Needle-Plate Geometry

In this study, a dielectric barrier discharge device with needle-plate electrodes was used to investigate the characteristics of the micro-discharge in argon at one atmospheric pressure by an optical method. The results show that there are two discharge modes in the dielectric barrier discharge, namely corona mode and filamentary mode. The corona discharge only occurs in the vicinity of the needle tip when the applied voltage is very low. However, the filamentary discharge mode can occur, and micro-discharge bridges the two electrodes when the applied voltage reaches a certain value. The extended area of micro-discharge on the dielectric plate becomes larger with the increase in applied voltage or decrease in gas pressure. The variance of the light emission waveforms is studied as a function of the applied voltage. Results show that very short discharge pulse only appears at the negative half cycle of the applied voltage in the corona discharge mode. However, broad hump (about several microseconds) can be discerned at both the negative half cycle and the positive half cycle for a high voltage in the filamentary mode. Furthermore, the inception voltage decreases and the width of the discharge hump increases with the increase in applied voltage. These experimental phenomena can be explained qualitatively by analyzing the discharge mechanism.     

Experimental investigations of enhanced glow based on a pulsed hollow-cathode discharge

In this work, the pulsed hollow cathode discharges at low pressure argon with an axial magnetic field were studied. The results indicate that the pulsed discharge is operated in an enhanced glow(EG) mode. Under the same conditions, the discharge current of the pulsed discharge is two or three orders higher than that of the direct current discharge. The spatial and temporal evolution of the light emission shows that, the current fluctuation at the rising edge of the pulse plays an important role for the EG discharge of pulsed hollow cathode, which forms a high-density, highcurrent and long-distance plasma column outside the cavity.     

The effect of the configuration of a single electrode corona discharge on its acoustic characteristics

A new sparker system based on pulsed spark discharge with a single electrode has already been utilized for oceanic seismic exploration. However, the electro-acoustic energy efficiency of this system is lower than that of arc discharge based systems. A simple electrode structure was investigated in order to improve the electro-acoustic energy efficiency of the spark discharge.Experiments were carried out on an experimental setup with discharge in water driven by a pulsed power source. The voltage–current waveform, acoustic signal and bubble oscillation were recorded when the relative position of the electrode varied. The electro-acoustic energy efficiency was also calculated. The load voltage had a saltation for the invaginated electrode tip,namely an obvious voltage remnant. The more the electrode tip was invaginated, the larger the pressure peaks and first period became. The results show that electrode recessing into the insulating layer is a simple and effective way to improve the electro-acoustic energy efficiency from 2% to about 4%.     

Study of the influence of discharge loop parameters on anode side on generation characteristics of metal plasma jet in a pulsed vacuum discharge

In a pulsed vacuum discharge, the ejection performance of a metal plasma jet can be effectively improved by preventing charged particles from moving to the anode. In this paper, the effects of resistance and capacitance on the anode side on the discharge characteristics and the generation characteristics of plasma jet are investigated. Results show that the existence of a resistor on the anode side can increase the anode potential, thereby preventing charged particles from entering the anode and promoting the ejection of charged particles along the axis of the insulating sleeve nozzle. The application of a capacitor on the anode side can not only absorb electrons at the initial stage of discharge, increasing the peak value of the cathode hump potential, but also prevent charged particles from moving to the anode, thereby improving the ejection performance of the plasma jet. In addition, the use of a larger resistance and a smaller capacitance can improve the blocking effect on charged particles and further improve the ejection performance of the plasma jet. Results of this study will provide a reference for the improvement of the ejection performance of plasma jets and their applications.     

Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application. Compared with conventional dielectric barrier discharge plasma actuators (DBD-PA), the sliding discharge plasma actuator (SD-PA) has the advantages of a large discharge area and a deflectable induced jet. To achieve the basic performance requirements of light weight, low cost, and high reliability required for UAV (Unmanned Aerial Vehicle) plasma flight experiments, this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators. In this study, the topology of the primary circuit of the microsecond pulse supply is determined, the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform, and the design of the actuation voltage, the pulse frequency modulation function and the construction of the hardware circuit are achieved. Using electrical diagnosis and flow field analysis, the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied, the optimal electrical actuation parameters and flow field characteristics are described.     

不同排放深度下温升作用对核电厂液态流出物近区稀释的影响研究

针对国内某典型内陆核电厂,基于一种三维水动力混合区模型及决策支持系统CORMIX(即康奈尔混合区专家系统),对核电厂液态流出物水底、水中淹没式排放及高于水面排放等排放情景共4种排放深度下,温排水温升作用对核电厂排出的液态流出物的近区稀释扩散能力的影响分别进行数值模拟。计算结果表明:温升对核电厂液态流出物近区稀释效果的影响规律主要依赖于流出物的排放深度;水底淹没式排放或水体中下层排放时,温升作用有利于液态流出物的近区稀释,水体中上层排放和高于水面排放时,温升作用对流出物近区稀释扩散能力产生明显的不利影响。     

Influence of heating on the discharge characteristics of a hollow cathode

Hollow cathodes are widely used as electron sources and neutralizers in ion and Hall electric propulsion. Special applications such as commercial aerospace and gravitational wave detection require hollow cathodes with a very wide discharge current range. In this paper, a heater is used to compensate for the temperature drop of the emitter at low current. The self-sustained current can be extended from 0.6 to 0.1 A with a small discharge oscillation and ion energy when the flow rate is constant. This is also beneficial for long-life operation. However, when the discharge current is high(1 A), heating can cause discharge oscillation, discharge voltage and ion energy to increase. Further, combined with a rapid decline of pressure inside the cathode and an increase in the temperature in the cathode orifice plate, electron emission in the orifice and outside the orifice increases and the plasma density in the orifice decreases. This leads to a change in the cathode discharge mode.     

Influence of nitrogen impurities on the characteristics of a patterned helium dielectric barrier discharge at atmospheric pressure

In this paper, a two-dimensional axisymmetric fluid model was established to investigate the influence of nitrogen impurity content on the discharge pattern and the relevant discharge characteristics in an atmosphere pressure helium dielectric barrier discharge (DBD). The results indicated that when the nitrogen content was increased from 1 to 100 ppm, the discharge pattern evolved from a concentric-ring pattern into a uniform pattern, and then returned to the concentricring pattern. In this process, the discharge mode at the current peak moment transformed from glow mode into Townsend mode, and then returned to glow mode. Further analyses revealed that with the increase of impurity level, the rate of Penning ionization at the pre-ionization stage increased at first and decreased afterwards, resulting in a similar evolution pattern of seed electron level. This evolution trend was believed to be resulted from the competition between the N₂ partial pressure and the consumption rate of metastable species. Moreover, the discharge uniformity was found positively correlated with the spatial uniformity of seed electron density as well as the seed electron level. The reason for this correlation was explained by the reduction of radial electric field strength and the promotion of seed electron uniformity as pre-ionization level increases. The results obtained in this work may help better understand the pattern formation mechanism of atmospheric helium DBD under the variation of N₂ impurity level, thereby providing a possible means of regulating the discharge performance in practical application scenarios.     

基于G-Link的实验数据采集传输系统

详细介绍了一个基于G-Link高速光纤数据传输系统;分析了以HDMP-1022／HDMP-1024为核心的光纤链路的基本构成和配置、激光管驱动电路、CIMT编码等内容。并利用G-Link设计了一个应用在风洞实验中的16通道数据采集和传输系统。     

Investigation of working pressure on the surface roughness controlling technology of glow discharge polymer films based on the diagnosed plasma

The effects of working pressure on the component, surface morphology, surface roughness, and deposition rate of glow discharge polymer(GDP) films by a trans-2-butene/hydrogen gas mixture were investigated based on plasma characteristics diagnosis. The composition and ion energy distributions of a multi-carbon(C_4H_8/H_2) plasma mixture at different working pressures were diagnosed by an energy-resolved mass spectrometer(MS) during the GDP film deposition process. The Fourier transform infrared spectroscopy(FT–IR), field emission scanning electron microscope(SEM) and white-light interferometer(WLI) results were obtained to investigate the structure, morphology and roughness characterization of the deposited films, respectively. It was found that the degree of ionization of the C_4H_8/H_2 plasma reduces with an increase in the working pressure. At a low working pressure, the C–H fragments exhibited small-mass and high ion energy in plasma. In this case, the film had a low CH_3/CH_2 ratio, and displayed a smooth surface without any holes, cracks or asperities. While the working pressure increased to 15 Pa,the largest number of large-mass fragments led to the deposition rate reaching a maximum of 2.11 μm h~(-1), and to hole defects on the film surface. However, continuing to increase the working pressure, the film surface became smooth again, and the interface between clusters became inconspicuous without etching pits.     

基于Evanescent Wave吸收的光纤传感器灵敏度计算分析

基于Evanescent Wave 吸收的U形光纤传感器是比较便于实用推广,可被用于化学传感的新型传感器.对于U形光纤传感器的渐逝波穿透深度和灵敏度进行了计算与分析,并与普通直线传感器做了比较,具体讨论了影响U形传感器灵敏度的几何参数因素和灵敏度优化公式.     

Effect of insulating oil covering electrodes on the characteristics of a dielectric barrier discharge

In this study, the effects of the fluid cooling and electric field line deformation were investigatedin a dielectric barrier discharge (DBD) plasma source. The DBD plasma jet is improved bycovering the ground electrode and a power electrode with insulating oil. We obtained positiveresults as insulating oil prevents arc formation, while it improved the supplied power and plasmajet length, and increased radical production. Radical production of this nonthermal plasma jet isstudied with polyvinyl alcohol–potassium iodide liquid.     

Numerical study of the influence of dielectric tube on propagation of atmospheric pressure plasma jet based on coplanar dielectric barrier discharge

A 2D fluid model was employed to simulate the influence of dielectric on the propagation of atmospheric pressure helium plasma jet based on coplanar dielectric barrier discharge (DBD). The spatio-temporal distributions of electron density, ionization rate, electrical field, spatial charge and the spatial structure were obtained for different dielectric tubes that limit the helium flow. The results show that the change of the relative permittivity of the dielectric tube where the plasma jet travels inside has no influence on the formation of DBD itself, but has great impact on the jet propagation. The velocity of the plasma jet changes drastically when the jet passes from a tube of higher permittivity to one of lower permittivity, resulting in an increase in jet length,ionization rate and electric field, as well as a change in the distribution of space charges and discharge states. The radius of the dielectric tube has a great influence on the ring-shaped or solid bullet structure. These results can well explain the behavior of the plasma jet from the dielectric tube into the ambient air and the hollow bullet in experiments.     

Experimental study on the parameter optimization and application of a packed-bed dielectric barrier discharge reactor in diesel particulate filter regeneration

To compensate for the shortcomings of the thermal and catalytic regeneration of the diesel particulate filter(DPF),a self-designed packed-bed dielectric barrier discharge(DBD)reactor for DPF regeneration was developed.The DBD reactor with the main active substance of nonthermal plasma(NTP)as the target parameter was optimized by adjusting the feed gas,packing particles(material or size),and cooling water temperature.Moreover,a set of optimal working parameters(gas source,O2;packing particles,1.2-1.4 mm ZrO2;and cooling water temperature,20℃)was selected to evaluate the effect of different O3 concentrations on DPF regeneration.The research results showed that selecting packing particles with high dielectric constant and large particles,as well as reducing the cooling water temperature,with oxygen as the feed gas,contributed to an increase in O3 concentration.During DPF regeneration,the following changes were observed:the power of the NTP reactor decreased to lower than 100 W,the O3 concentration increased from 15 g m-3 to 45 g m-3,the CO and CO2 volume fractions of the particulate matter decomposition products increased,and the peak regeneration temperature increased to 173.4℃.The peak temperature arrival time was 60 min earlier,indicating that the regeneration rate of DPF increased with the increase in O3 concentration.However,the O3 utilization rate(the amount of carbon deposit removed per unit volume O3)initially increased and then decreased;when the O3 concentration was set to 25 g m-3,the highest O3 utilization rate was reached.The packed-bed DBD technology contributed to the increase in the concentration of NTP active substances and the regeneration efficiency of DPF.It provides a theoretical and experimental basis for high-efficiency regeneration of DPF at low temperatures(＜200℃).     

Experimental Study on the Velocity and Efficiency Characteristics of a Serial Staged Needle Array-Mesh Type EHD Gas Pump

The ionic wind has good application prospects in the fields of air flow control and heat transfer enhancement. The key for successful applications is how to imp...