Numerical Simulation of Gasdynamic Flows Formed by an Electric Arc in an External Transverse Magnetic Field

The results of numerical investigations of an electric arc in an external transverse magnetic field are given. The effect of external controlled discharge parameters and of the magnetic field of the electrodes on the characteristics of a flow of arc-discharge plasma is treated. Some singularities of the flow formed by an electric arc in an external transverse magnetic field are revealed.     

微阴极电弧推力器放电特性研究

相对于大型卫星, 微纳卫星具有模块化、发射灵活、可编队飞行等特点。微阴极电弧推力器 (μ-CAT) 是一种适用于微纳卫星的推进装置, 具有体积小、质量轻、功耗小等特点。本文分析了μ-CAT的工作原理, 对推力器结构进行了设计, 并利用高真空电推进实验平台, 完成了对推力器放电特性实验装置的搭建。在高真空条件下对μ-CAT进行了点火试验, 测试了推力器放电时的伏安特性曲线, 分析了单脉冲周期的电压电流变化规律。随后分别在有无外加磁场的条件下, 采用法拉第探针测量了μ-CAT等离子体离子电流空间分布情况, 实验结果表明磁场具有减小等离子体羽流发散角的作用。研究工作可为后续推力器放电参数优化设计和羽流测量工作提供理论指导。     

Numerical Analysis of the Characteristics of an Arc in Laminar and Turbulent Gas Flows

The equations of magnetic gas dynamics are used to calculate the characteristics of an electric arc in a plasmotron channel versus the gas flow rate. The results obtained with the aid of the laminar and the two-parameter k– model of turbulence with allowance for deviations from equilibrium in the plasma and for the swirling of the gas are compared with experimental data. The stability of a laminar flow to the effect of weak hydrodynamic perturbations is investigated.     

The Use of the Method of Fictitious Regions to Calculate the Characteristics of an Electric Arc

The possibility is examined of using the method of fictitious regions to calculate the characteristics of an electric arc in a multiply connected region. Analysis of the results points to the legitimacy of using this method.     

Effect of Gravity on Arc Shape in GTA Welding-for Low Electric Arc Current

Gas tungsten arc (GTA) welding was performed both in a microgravity environment and in a terrestrial environment,and the arc shapes in both environments were compared. A microgravity condition was obtained using the free fallsystem at the Japan Microgravi     

Vacuum Arc Discharge on Integrally Cold Cathode

Initial researches of the existence of a cathode spot on the working surface were conducted in vacuum arc plasma sources of the coaxial design. The moving of the cathode spots on the limited sizes working surface does not give full picture of the development of the arc discharge. This article describes the vacuum arc plasma source of extended design generating the directed belt plasma stream and operating in pulse mode. The researches carried out give additional information about development of the cathode spots of the vacuum arc discharge. It is found that the speed of the cathode spots' motion depends on the cathode temperature.     

Conditions of Burning of an Arc with a Recoverable Carbon Cathode

A system of equations of integral balances are solved simultaneously with a heat problem in order to determine the parameters of the cathode region of an arc with a recoverable carbon cathode formed from a plasma-generating medium. The solution corresponding to the conditions of recovery is identified in the set of solutions of this system of equations, obtained by varying the input parameters. It is demonstrated that only one solution out of this set corresponds to the mode of carbon cathode recovery, which is indicative of the sensitivity of the recivery mode to the arc parameters in actual practice.     

Cathode Spots of Vacuum Arc Discharges

Vacuum arc discharge is used for formation of pure metal and complex combined coatings, and also for the impact of the discharge on a surface to remove superficial contaminants. Physical processes observed in an arc discharge are mostly determined by the behavior of cathode spots, which are fundamentally unstable plasma formations and are characterized by a certain value of average lifetime. Reliable stabilization of the cathode spots and controlling their movements on the working surface grants the technology a grater importance in application.     

真空阴极弧离子镀阴极斑点的移动研究

建立了真空阴极弧离子镀圆形平面靶侧面引弧时 ,阴极斑点的受力模型 ,分析了影响电弧运动的因素 ,改进了圆形平面靶侧面形状 ,大大提高了石墨靶阴极斑点从侧面到靶平面的过渡速度     

Characteristics of the Development of Electric Discharge between Jet Anode and Liquid Cathode

We present experimental results on the behavior of the burning of electrical discharge between a nonuniform jet anode and liquid cathode and of the discharge voltage and current pulsations for various voltages of the power supply. We determine the frequency spectrum of the discharge voltage oscillations, as well as the temperatures on the electrolyte cathode surface, by means of infrared thermography and pyrometer.     

Effect of the Angular Distribution of Cathode Ions on the Current Flow in a High-Current Vacuum Arc

The effect of the angular distribution of cathode ions on the parameters of a vacuum arc is investigated. It is shown that, at current densities characteristic of a high-current arc, collisions of flows of fast ions from different cathode spots may result in a high value of the ion temperature at the cathode plasma boundary. The boundary in current density of the region of a stable current flow as a function of the width of angular distribution of cathode ions is determined. It is found that, in the region of supersonic flow of ions, the permissible value of the current density drops rapidly as the angular distribution width increases, and in the subsonic region, it rises rapidly. An expression is obtained for the maximum possible ion sound velocity and for the equivalent critical ion velocity. Two- and three-fluid hydrodynamic models are used to perform calculations that illustrate characteristic distributions of parameters in the discharge gap. Analysis of the calculation results makes it possible to discuss the characteristic features of current flow in a vacuum discharge.     

Erosion of a Copper Cathode in a Nonstationary Arc Spot. I. Experimental Investigation

A study has been made of the dependence of the erosion of a copper cathode of an electricarc heater on the basic operating parameters: the arc current, the velocity of movement of an arc spot, and the temperature of the electrode surface. The experiments were conducted in a coaxial electricarc heater with a magnetic movement of the arc in an air medium for an arc current of 95–480 A and a magnetic field of 0.005–0.417 T. The duration of the experiment, the axial velocity of a plasmaforming gas, and the flow rate of a cooling water were held constant. It has been shown that there are two different erosion regimes: the microerosion regime characterized by a weak dependence on the current and the macroerosion regime with a strong dependence on the current; the transition from one regime to the other is realized upon the attainment of the critical value of the current, dependent on the magnetic field and the thermal regime of the electrode. The existence of a velocity interval in which the specific erosion is minimum has been shown, which confirms the predictions of the earlier thermal model of erosion of cold electrodes.     

Erosion Characteristics of Copper-Based Composite Electrodes in an Electric Arc of Variable Length with Transverse Gas Blowing

We present experimental data on the erosion of electrodes made of copper-based pseudoalloys during contact breaking at current amplitudes up to 150 kA in nitrogen at a pressure of ~2 MPa with transverse gas blowing. The electric-erosion characteristics of copper–iron pseudoalloy CuFe (85/15%) electrodes obtained by laser layer melting, as well as CuFe (70/30%) and CuW (25/75%) pseudoalloy electrodes fabricated by traditional powder technology (sintering of pressed powder compacts) are reported. The specific erosion of electrodes in variable-length arc amounts to ~1 mg/C, which somewhat exceeds the value observed for a fixed-length arc discharge gap.     

Carbon Nanotubes Grown on the Surface of Cathode Deposit by Arc Discharge

Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH₄ gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH₄ gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH₄ gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm.     

Carbon Nanotubes Grown on the Surface of Cathode Deposit by Arc Discharge

Abstract

Carbon nanotubes prepared by de arc discharge of graphite electrodes in He and CH₄ gas took markedly different morphology. Thick nanotubes embellished with many carbon nanoparticles were obtained by evaporation under high CH₄ gas pressure and high arc current. Thin and long carbon nanotubes were obtained under a CH₄ gas pressure of 50Torr and an arc current of 20A for the anode with a diameter of 6mm.     

基于标准阴极特性的面齿轮阴极设计方法

目的 解决电解加工过程中,简单曲面阴极设计方法不能保证面齿轮加工精度的问题。方法 利用标准阴极进行正交试验,得出钢制面齿轮的最优电解工艺参数。利用该工艺参数对阴极重新设计,加工试件,根据试件的测量结果对原始阴极进行修形,得出最终阴极形状。结果 通过对正交试验数据进行处理,得出钢制面齿轮的最优电解工艺参数为K=20, U=10 V, v=0.6 mm/min;根据试件的误差测量结果,推导出最优修形数为0.4602。结论 此阴极设计方法所设计的阴极能保证面齿轮的加工精度,而且能够加工出IT7级精度制件,同时为复杂型面的高精度电解加工方案提供了一种可行的阴极设计方法。     

Cathode Drop of the Potential of a Vacuum Arc of Metals

The basic mechanisms of ionization in the cathode spot of a vacuum arc are considered. It is shown that the singly charged positive ions formed here are a result of the collision ionization of the evaporated atoms of a metal by electrons. On this basis the assumption is made that the cathode drop of the potential of the vacuum arc of metals is determined by the energy of ionizing electrons at which the ionization section attains its maximum.     

Numerical Investigation of Bubble Induced Marangoni Convection: Some Aspects of Bubble Geometry

Thermocapillary or Marangoni convection is a surface tension driven flow that occurs when a gas–liquid or vapor–liquid interface is subjected to a temperature gradient. In the past, the contribution to local heat transfer arising from Marangoni convection has been overlooked as insignificant since under earth gravity it is overshadowed by buoyant convection. This study numerically investigates some aspects of bubble size and shape on local wall heat transfer resulting from Marangoni convection about individual bubbles on a heated wall immersed in a liquid silicone oil layer (Pr = 110) of depth 5 mm. It was found that increasing bubble volume causes an increase in the area over which Marangoni convection has affect. Heat transfer therefore increases with bubble size. Over the effective area, the surface averaged hot wall heat transfer is not affected greatly by bubble shape. The surface averaged heat transfer over the effective area on both the hot and cold walls is affected dramatically by bubble size, but the increase is more profound on the cold wall.     

Structure of the Welding Arc Cathode Spot with a Nonconsumable Electrode

The cathode spot autographs on a glass surface are investigated through an electron microscope, with a magnification up to 100000. We discover that the welding arc cathode spot consists of separate cells with the substructure, current channels, 10–60 nm in diameter. We acquire color photographs of the welding arc cathode spot with the cathode torch. Photograph processing through different filters reveals the shape of the cathode spot and the cathode torch. We perform the estimate calculations of the current density in the welding arc cathode spot substructure.     

层状板岩动力破坏特性数值试验研究

为研究层理面数和冲击载荷对层状板岩动力破坏特性影响,利用LS-DYNA有限元软件模拟了层状板岩试件在不同冲击速度下的SHPB实验,再现了SHPB实验过程中的加载波形和层状板岩试件的破坏过程,模拟结果与实验结果吻合度较好。研究结果表明:层状板岩试件的耗散能量随层理面数的增加而增加,双层、三层和四层板岩试件相比单层板岩试件耗散能量的增长分别为0.2%、0.4%和1.87%;试件破坏开始于端面周边,滞后于应力峰值,当冲击速度为6.5 m/s时,层状岩石试件以轴向劈裂破坏为主,冲击速度为12 m/s和20 m/s时试件的破坏模式为轴向劈裂破坏、径向剪破坏和端面拉压破坏的混合破坏。