直流纯氩层流等离子体射流的长度变化

采用主要由阴极、阳极以及介于阴极和阳极之间的中间段组成的直流非转移式电弧等离子体发生器,在大气压条件下,比较系统地研究了纯氩层流等离子体射流的长度随着弧电流、气体流量以及发生器结构而变化的规律。结果表明:层流射流的长度随弧电流和工作气流量的增加而增长;层流向湍流流动转变的临界气流量值随弧电流增大而提高;在发生器的伏安特性呈大梯度变化的情况下,射流长度随弧电流的变化幅度增大。     

直流电压等离子体点火器点火特性研究

使用自行设计的等离子体点火装置,对极间电流随进口氩气压力的变化规律以及不同进口氩气压力和工作电流条件下等离子体点火器出口射流特性进行了实验研究。利用四通道CCD光谱仪测量了点火器出口处的发射光谱特征,并计算了等离子体的电子温度。结果表明,极间电流随进口氩气压力的增大而逐渐减小,等离子体点火器的射流长度随进口氩气流量的增大先增大后减小,随工作电流的增大而增大,等离子体点火器的工作电流随进口氩气流量的增大而减小,随电源输出电流增大而增大,等离子体射流的电子温度随氩气流量的增大而降低,随工作电流的增大而升高。所得结果对等离子体点火系统在航空发动机的实际应用具有一定的指导意义和参考价值。     

PEMFCs的膜及阴极催化层数值模拟

本文提出了一个质子交换膜燃料电池的膜和阴极催化层的一维非稳态数学模型,模型考虑了电化学反应及反应中的传质过程。本文结合算例分析了燃料电池膜及阴极催化层的性能,结果能验证燃料电池内阻理论。论文结果表明:(1)随着输出电流密度的增大,氧浓度分布不均匀性增大; (2)阴极催化层厚度减小,可提高电池输出电压; (3)电池进口处氧气摩尔浓度增大,可增加电池的输出电压。     

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简要介绍了EAST装置远红外激光干涉仪光源——DCN激光器的工作原理、结构和相关改进。DCN激光器采用He、CD4、D2和N24种工作气体。实验过程中,通过调节气体压强和阴极电流、改变各种工作气体配比等手段优化DCN激光器输出功率。实验结果显示：输出功率随电流的增大会达到饱和,在电流为1.0A输出功率达到最大;输出功率随压强先增大后减小,在压强为32Pa时达到最大值;工作气体的最佳配比为He： CD4： D2： N2=2：3：5：3。     

PEMFC电极表面液态水生成的可视化研究

本文设计了一个可视化直流道单片电池,通过高倍高速数字摄影装置观察记录了阴极流道壁面和气体扩散层表面的凝结水出现和成长过程,并分析了电池运行温度,阴极气体压力,气体化学当量比以及气体加湿度等参数对阴极流道内液态水的生成和排出的影响。     

生物过滤器中非均匀性流动的数值研究

生物过滤技术因其具有有效性、低成本和环境友好等优点引起了人们的广泛关注.该技术主要通过生物过滤器去除含有H2S等废气的有毒有害气体.运用格子Boltzmann方法对三种生物过滤器模型中多孔介质的非均匀性流动进行了数值模拟.数值模拟结果表明,多孔介质的性质和进口流动条件对临界Rayleigh数有显著影响,临界Rayleigh数随着多孔介质的孔隙度和Darcy数的增大而逐渐变小,并随着进口Reynolds数的增大而逐渐变大.所得结果可望为生物过滤器的优化设计提供一个合理的理论依据.     

连续辉光放电波导型远红外氘化氰激光器输出性能优化

简要介绍了EAST 装置远红外激光干涉仪光源--DCN 激光器的工作原理、结构和相关改进。DCN 激光器采用He、CD₄、D₂ 和N₂ 4 种工作气体。实验过程中,通过调节气体压强和阴极电流、改变各种工作气体配比等手段优化DCN 激光器输出功率。实验结果显示：输出功率随电流的增大会达到饱和,在电流为1.0A 输出功率达到最大;输出功率随压强先增大后减小,在压强为32Pa 时达到最大值;工作气体的最佳配比为He: CD₄: D₂: N₂=2: 3: 5: 3。     

不同流场下进气对质子交换膜燃料电池性能的影响

流场的结构对于质子交换膜燃料电池(PEMFC)的水管理和气体的传递具有十分重要的影响,相关研究一直是燃料电池的研究热点与重点。本文以纯氧气和空气作为阴极氧化剂,通过电池的性能测试、极化曲线和电化学阻抗分析等原位实验,分析了气体的流动与传输、不同流场下的电流密度、入口反应气体浓度等条件对电池性能的影响。实验结果表明,提高氧气浓度可以获得更好的质子交换膜燃料电池性能和最小化活化损失,纯氧气、波状流场的使用效果随进气量的变化而有明显的变化。     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

Potential profile near the virtual cathode in presence of charged dust

In this work, concept of virtual cathode and its existence in dusty plasma has been studied by theoretical and numerical analysis. Using basic equations of charge dust, ions, and electrons, the non‐monotonic behaviour of the potential in presence of charged dust has been calculated and plotted as a function of dust density. It has been found that there is a change in potential between cathode and sheath potential and subsequently changes the threshold wall temperature as compared to that of without dust conditions. The threshold wall temperature has been increased due to the ability of micro‐particles acquiring electron charge and hence, reducing potential at the wall. Further, for different values of α (depends on dust density); threshold temperature remained the same for observed virtual cathode. Hence, behaviour of potential has been plotted as a function of α with increasing wall temperatures for two dust charge values (1 and 1,000). Considering no dust charge, it has been observed that, at lower dust density, double layer like structure is formed near the emissive wall. But this double layer structure gets diminishes with increasing dust density. Hence, below a threshold dust density, virtual cathode near to the emissive wall is not possible. While for Z_d = 1,000, the formation of virtual cathode appeared even at very small dust density. However, irrespective of variation of potential difference near the wall and existence of virtual cathode at different emission regime the threshold wall temperature remains same. Effect of dust potential dependency on threshold wall temperature has also been discussed in this study.     

An experimental study of relative humidity and air flow effects on positive and negative corona discharges in a corona-needle charger

In this paper, the effects of inlet air RH and air flow rate on positive and negative corona discharges in a corona-needle charger have been experimentally studied and discussed. Its corona discharge characterizations in terms of current-to-voltage relationships of the corona-needle charger on the effects of inlet air RH and air flow rate were evaluated at applied corona voltages between 0 and 3.1 kV, an air flow rates between 5 and 15 L/min, a relative humidity between 20 and 90%, and an operating pressure of about 101.3 kPa. Experimental results were shown that discharge current is strongly affected by the RH level of the inlet air. The positive discharge current was found to be decreased with increasing RH value at RH values below 60% and increased with increasing RH value at RH value above 60% in the same corona voltage. The negative discharge current was found to be stable with increasing RH value at RH values below 40% and increased with increasing RH value at RH value above 40% in the same corona voltage. For the air flow rate effects, the positive discharge current was found to slightly decrease when the air flow rate increased at RH value below 90% and to increase with the air flow rate at RH value of 90%. For the negative corona, the discharge current was also found to monotonically decrease when the air flow rate increased.     

Effect of relative humidity on current–voltage characteristics of an electrostatic precipitator

This paper aims at characterizing the behavior of dc corona discharge in wire-to-plane electrostatic precipitators (ESPs) as influenced by the relative humidity (RH) of the inlet air. The current–voltage characteristics and time evolution of the current are analyzed. Experimental results show that discharge current is strongly affected by the RH level of the inlet air. For instance, the time-averaged current is lower at higher RH for a given voltage, except when RH = 99%. Time evolution of the discharge current is affected by the humidity especially in the case of negative corona.     

Plasma localization in an extended hollow cathode of the plasma source of a ribbon electron beam

The plasma density distributions in the slit aperture of the extended rectangular hollow cathode of the source of a ribbon electron beam are investigated experimentally. It is found that a local maximum whose parameters are determined by the discharge current appears in the density distribution when the slot width is less than a certain threshold value. This maximum results in an inhomogeneous current density distribution in the beam. It is shown that the appearance of the local maximum in the plasma density is related to the overlapping of the ion sheaths in the slit aperture of the hollow cathode.     

Field emission performances of CNTs bundles array

The field emission performances of normal-gate cold cathode, which is composed of different multi-wall carbon nanotubes (MWCNTs) bundles array are calculated. The device parameters such as the arrangement of bundles, array density, gate location, gate voltage, anode voltages and anode–cathode distance affect the field emission properties, which is discussed in detail. The results reveal that the hexagon bundles array needs a lower threshold voltage than square array to reach high field enhancement factor and large emission current density. The emission current density is two orders larger than that of the oxide emitter. The optimal bundles array densities of hexagon and square array to get field enhancement factor are 0.0063 and 0.00375 μm⁻², respectively. Meanwhile, the field emission performances are impacted critically by gate location and gate voltage. Field emission properties changed little while the anode–cathode distance varies within tens of micrometers, which increases the process-friendliness of CNTs field emission devices.     

Application of Electron-Beam Ionized Discharges to Switches?a Comparison of Experiment with Theory

A theoretical investigation of high-pressure discharges ionized by an external electron beam (e-beam) was conducted. Only when secondary emission from the cathode and electron-impact ionization of metastable states were included in the analysis did calculated current-voltage (I-V) characteristics for argon and methane discharges compare well with experimental data. The I-V characteristics obtained reveal a sharp rise in the current at a certain threshold voltage. This threshold voltage and the entire I-V characteristic are shifted to lower voltages when metastable ionization is significant. Below the threshold voltage and at low external ionization source strengths, a region of negative differential conductivity is obtained. In the high-current region, the I-V slope is controlled by the secondary emission coefficient. The additional cathode sheath ionization from secondary emission and ionization from metastable states significantly reduces the discharge voltage. This important effect can be used to reduce e-beam switch losses and increase lifetime through judicious gas mixture selection and proper cathode conditioning.     

环形磁场金属等离子体源冷却流场的数值模拟与优化

环形磁场金属等离子体源作为一种全新的等离子体源结构,可用于产生高度离化、无大颗粒、高密度的离子束流,但传统流道结构不能保证其高效、均匀散热,大功率工作时可能引起密封胶圈的烧蚀失效,需对其冷却流场进行优化设计.利用Solidworks Flow Simulation软件对等离子体源冷却流道进行模拟,分析出入水孔分布角度、孔数、孔径以及入水孔高度对冷却效果的影响规律,并对流道结构参数进行优化.结果表明,增大水孔的周向分布范围,有利于提高散热的均匀性;入水孔设置在结构上层有利于减少冷却水的温度分层现象,使铜套和密封胶圈都处于较好的冷却状态;适当减小孔径有利于增大冷却水射流速度,增大湍流程度强化传热,提高换热效率.优化后的流场结构可以提高冷却水的利用率,在相同流量条件下获得更好的冷却效果,改善等离子体源的放电稳定性,为环形磁场金属等离子体源的冷却结构设计提供理论依据.     

Localization of plasma in the extended hollow cathode of a ribbon-electron-beam plasma source at forevacuum pressures

The results of a study of the plasma density distribution in the slit aperture of a right-angled extended hollow cathode used in a ribbon-electron-beam plasma source operating at forevacuum pressures (1–10 Pa) are presented. It is shown that a local peak of plasma density appears in some region of the slit aperture as the slit width is decreased. This results in the appearance of a region of increased current density when the ribbon beam forms. The uniformity of the beam current density distribution is additionally disturbed by the reverse ion flow whose effect on the emission properties of the plasma is significant in the region of elevated pressure. A model which describes the development of plasma density nonuniformity in a hollow cathode is proposed which is based on the idea that the electron current flows predominantly through the slit aperture regions that are associated with local openings of the cathode layer ion sheaths. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–9, June, 2007.     

Design and manufacture of planar GaAs Gunn diode for millimeter wave application

GaAs-based planar Gunn diodes with AlGaAs hot electron injector have been successfully developed to be used as a local oscillator of 76 GHz in monolithic millimeter-wave integrated circuits.We designed two kinds of structure diode,one has a fixed distance between the anode and cathode,but has variational cathode area,the other has a fixed cathode area,but has different distances between two electrodes.The fabrication of Gunn diode is performed in accordance with the order of operations:cathode defining,mesa etching,anode defining,isolation,passivation,via hole and electroplating.A peak current density of 29.5 kA/cm 2 is obtained.And the characteristics of negative differential resistance and the asymmetry of the current-voltage curve due to the AlGaAs hot electron injector are discussed in detail.It is demonstrated that the smaller size of active area corresponds to the smaller current,and the shorter distance between anode and cathode also corresponds to the lower threshold voltage and higher peak current,and hot electron injector can effectively enhance the radio frequency conversion efficiency and output power.