电弧增材成形中熔积层表面形貌对电弧形态影响的仿真

电弧增材成形常采用单道多层或多道搭接的熔积方式,不同的熔积方式下对应的熔积层表面形貌不同,从而影响电弧的形态及其传热传质过程.本文建立了纯氩保护电弧增材成形的电弧磁流体动力学三维数值模型,以及不同表面形貌的熔积层模型,并在保持阳极与阴极之间距离和熔积电流不变的条件下,通过模拟计算获得增材成形特有的单道和多道搭接熔积条件下的不同表面形貌对应的电弧形态以及相应的温度场、流场、电流密度、电磁力、电弧压力分布.数值模拟结果表明:平面基板上起弧情况下电弧中心具有较高的温度、速度、电流密度以及压强;单道多层熔积情况下熔积层数对电弧的各个参量影响较小;多道搭接熔积情况下电弧呈非对称分布,电弧中心温度较前两者低,电流密度、电磁力和电弧压强的分布偏向熔积层一侧.     

Zur Theorie der Wirbelstabilisierung in einem zylindrischen Lichtbogen

Contrarily to well known cylindrical, whirl-stabilized electric arcs with rotating walls or with nearly tangential gas inlets, we discuss a new geometry of an electric arc for producing a whirl around the axis. These investigations have been performed for transferring the theory to a torus arc in a similar way. By using a numerically calculated temperature distribution the hydrodynamic properties are studied taking into consideration the single-fluid model of plasma physics. The results are compared with our experiments and those of other institutes. They agree well and give hope to a stabilizing effect for an electric arc of this geometry. The analytical distributions of the velocities and the pressure are calculated on the basis of perturbation theory. The results are applied to a nitrogen arc at a pressure of one atmosphere and for a definite set of parameters.     

Downstream Conditions in a Constricted ARC with Radial Injection

The thermal, flow and electrical conditions are presented for the downstream portion of an argon arc with local fluid constriction. The arc is initially wall-stabilized in a 10 mm diameter water-cooled constrictor and at some point after flow becomes fully developed the arc is constricted by a radial inward jet. The redevelopment of the flow downstream of the injection slot is investigated by measurements of the pressure drop, wall heat flux and electric field. It is observed that redevelopment proceeds roughly as predicted by classical theory. Measurements of the electric field indicate that the region of maximum constriction is limited in extent.     

分流器形式炮口消弧装置的电路模拟优化与试验

针对轨道炮电枢出炮口时拉弧问题,提出了一种基于分流器形式的炮口电弧抑制方案。以固体电枢为研究对象,采用Simulink软件根据发射器与消弧装置的电气参数建立含有炮口消弧装置的发射系统仿真模型,目的是通过对消弧装置电气参数不同阻抗值的仿真计算,实现消弧装置电气参数与发射系统电气参数的最佳匹配,达到降低消弧支路对电枢出炮口速度的影响,同时有效地抑制炮口电弧。由于与消弧装置串联的电枢前方轨道阻抗在消弧支路阻抗中占比很大,通过消弧装置阻抗电阻、电感优化调整,实现电枢在膛内运动起始阶段,消弧支路的阻抗远大于电枢支路的阻抗,发射电流大部分都流过电枢,保证了电枢的加速运动。随着电枢向炮口方向运行,消弧支路阻抗快速减小,同时在磁通压缩作用下,消弧支路中电流快速增加,电枢支路电流减小,但由于电枢前后方磁场对其都是推进作用,电枢出炮口速度基本不受影响,保持较高的系统效率;电枢出炮口后,消弧支路的阻抗小于电弧的阻抗值,建立合理的电弧快速消引条件,消弧支路电流远大于电枢上电流,发射系统的剩余能量可通过消弧装置释放,降低炮口拉弧对发射性能的影响。经过消弧装置的电阻和电感多参数值的计算与分析,最后确定与文中发射系统匹配的消弧装置电阻约为1 mΩ,电感约为0.1 μH。结合发射装置结构,设计出的消弧装置电阻为1.32 mΩ,电感为0.124 μH,在搭建的发射系统仿真模型中对其进行了充电电压3 kV等级的发射仿真计算,在充电电压3 kV的发射能量等级下进行了消弧发射试验,仿真结果与试验结果具有较好的一致性,消弧效果良好。     

Determination of the characteristics of an electric arc plasmacontaminated by vapors from insulators

Results are presented from an experimental study (at atmospheric pressure) carried out on plasma penetrated by vapors from different industrial insulators. The data describe the influence of each insulator type upon the characteristics of the electric arc plasma, i.e. the resulting increase of the temperature, electronic density, electric field, and extinction velocity of the arc. Measurements were made spectrometrically and by means of probes     

Study of the Nitrogen Arc under Reduced Pressure

The paper presents a model of arc in a d.c. vortex plasma torch which allows to determine distributions of temperature and plasma electron density in conditions of reduced pressure. The model makes it possible to elucidate voltage-current characteristics of the arc at different pressures and its dynamic behaviour connected with the phenomenon of the electric arc root displacement. The experimental research also determined voltage-current characteristics for different flow rates and pressures. The fluctuations of the arc current and the arc voltage were measured. The corresponding wave shapes were analysed by Fast Fourier Transform. The frequency variations with flow rate, arc current and pressure were studied and discussed.     

Results of a computer simulation of an arc plasma in a curved discharge tube

In this paper are presented some results of numerical calculations of an arc plasma in a curved geometry. More about the mathematical methods (relaxation methods, transformation of the basic equations to toroidal coordinates) are to be found in earlier papers (Refs.^4,6,7). In particular the effect of the curvature on thermal, magnetic, electric and dynamic quantities in a wall stabilized electric arc at atmospheric pressure will be discussed.     

Dynamic behaviour of alternating current arc discharge in a multi‐arc generator at atmospheric pressure

In this letter, a multi‐arc generator with three high‐voltage electrodes and a common grounded one was developed for the purpose of obtaining large area and steady arc plasma at atmospheric pressure. Three typical discharge states were found in the multi‐arc generator: independent movement of three arc columns, confluence of two arc columns, and confluence of three arc columns. The three discharge states cyclically occur on the evolution of the arc discharge and their duration is influenced by the power dissipation and plasma working gas flow rate. With an increase of discharge power and a decrease of the gas flow rate, the duration of multiple arc confluence increases, which contributes to the suppression of the fluctuation amplitude of each arc. Frequency domain analysis of the arc voltage envelope shows that the frequency of arc fluctuation increases in the multi‐arc mode in the multi‐arc generator compared to that in the single arc mode.     

Anode Heat Transfer in a DC Electric ARC with Superimposed Axial Flow

A DC electric arc is operated in argon at pressures between 100 and 760 mm Hg, axial flow velocities from 0 to 100 m/sec, and currents from 50 to 200 amps to assess the influence of these parameters on anode heat transfer using a double-anode configuration consisting of two plane, parallel anodes. Since the anode arc attachment size is appreciably smaller than the anode surface area in these experiments, a method is developed using an optical and/or floating potential probes for measuring the size of the near-anode arc column. The relative variation of two perpendicular dimensions of the near-anode arc column for variation in the arc operating parameters (pressure, flow velocity, current, anode separation) are measured. The results reveal that the cross section of the nearanode column is not circular and the average local heat fluxes show a strong dependence on the gas pressure.     

Vacuum breakdown on metal surfaces

The unipolar arc model is described. Experimental proof that unipolar arcing represents a discharge form which easily leads to explosive plasma formation is provided. Using a laser-produced plasma, it has been demonstrated that unipolar arcs ignite and burn on a nanosecond time scale without any external electric field being applied. Similar unipolar arc craters have been observed on the cathode surface of a pulsed vacuum diode with an externally applied field of 0.5 MV/cm. The experimental results show that cathode spots are formed by unipolar arching. The localized buildup of plasma above an electron-emitting spot naturally leads to a pressure gradient and electric field distribution which drives the unipolar arc. The high current density of a unipolar arc provides explosive plasma formation     

Numerical model of the anode region of high-current electric arcs

A two-dimensional, two-temperature axisymmetric numerical model has been formulated for the flow-affected region and the boundary layer in front of high-intensity electric arc anodes. The plasma flow is laminar, steady, incompressible, and the plasma composition is found from the diffusion equation because chemical nonequilibrium is expected. Computational results are obtained for an atmospheric pressure argon arc considering two different situations: a free-burning electric arc and an arc with a constrictor tube. The solutions indicate two different anode attachments modes-a constricted and a diffuse attachment. It is found that under the conditions considered in the calculations, the gradient-induced current densities become significant at distances in the order of 1 mm from the anode surface. The thermal anode boundary layer is compressed with increasing current. The thickness of the thermal boundary layer for the constricted mode is approximately three times smaller than for the diffuse mode. A reversal of the electric field strength occurs over the entire thickness of the boundary layer in all calculated cases. A satisfactory agreement is reached between the calculated heat flux values and experimental results obtained for a 200-A free-burning electric arc     

Radiation of electric arc burning in argon

Using real experimentally obtained integral values, the paper deals with modelling of electric arc stabilised by flowing gas. Attention is focused namely on approximate estimation of radiation coefficient of argon. A designed model of electric arc burning in argon of atmospheric pressure inside arc heater’s anode channel is described. The model makes it possible to compute axial and/or radial dependencies of some quantities of interest (temperature, velocity, electric field intensity, arc radius, etc.), and subsequently to judge energy exchange between the arc and its surroundings. Sets of model’s input data, including arc voltage, arc current, argon flow-rate, and flow-rates and temperatures of water cooling individual parts of the arc heater, have been measured during numerous experiments. In a studied case with relatively high argon flow-rate, radiation has been found to be prevailing mechanism of energy transfer from arc to anode channel walls. Based on this finding, techniques have been designed for simple approximate estimation of radiation coefficient of argon in a limited extent of temperatures. As an example, they have been tested on a particular set of measured and computed data. Argon radiation coefficient estimated in this way has been compared with the results of theoretical computations carried out by other authors. Considering simplifications used and differences between a real situation and an ideal theoretical model, agreement of the results is within satisfactory limits.     

The DC Arc in a Supersonic Nozzle Flow

The boundary layer integral method at its second level of approximation has been used to study the DC arc in a supersonic nozzle flow. It is shown that with the inclusion of the arc momentum balance, the critical point of the flow is, generally, not the sonic point of the external flow. The speed, at which a disturbance propagates relative to the external flow, is in general supersonic and is dependent on the arc conditions. The arc model is capable of predicting the axial electric field, the arc size and the axial pressure distribution as a function of current. For affinely related nozzles, the solution is determined by a parameter N, which is related to zt, the stagnation condition and the nominal current density at the throat (I/At). Numerical results are given for a particular nozzle shape although the method of analysis is general. Practical implications as regards nozzle design for a gas blast circuit breaker are briefly discussed.     

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利用自行设计的快速移动静电探针对大气压下以氩气为工质的大尺度磁分散电弧等离子体进行诊断,分析了探针电压与电流的波形,绘制探针伏安特征曲线(U-I曲线),得到了发生器轴线方向等离子体波动特性以及电子温度沿轴线的变化趋势.发现等离子体发生器中心具有回流区,得到了电弧等离子体的大致体积.     

Der Einfluß einer Krümmung auf eine wandstabilisierte Lichtbogenentladung

In this paper the analysis of gas heating phenomena in wallstabilized toroidal electric arcs is derived and the results are applied to a nitrogen arc at a pressure of one atmosphere. These investigations have been performed on the basis of the single-fluid model of plasma physics taking into consideration the thermal properties of the wall material. By using a differential method it is outlined how the equation of energy is solved not only in the arc but also in the wall.     

Zur Theorie der Gasaufheizung in axialsymmetrischen,wandstabilisierten Lichtbögen

In this paper the analysis of gas heating phenomena in wallstabilized electric arcs with axial gas flow derived in an earlier paper is applied to a nitrogen arc at a pressure of one atmosphere. For this reason the behaviour of the inlet length, the perturbation quantities and the integral characteristic values of such an arc is discussed and their parameter dependences are investigated. The results give the best parameter values for getting the highest enthalpy flux and the best efficiency of the arc heater.     

Gyrocenter shift of low-temperature plasmas and the retrograde motion of cathode spots in arc discharges

The gyrocenter shift phenomenon explained the mechanism of radial electric field formation at the high confinement mode transition in fusion devices. This Letter reports that the theory of gyrocenter shift is also applicable to low temperature high collisional plasmas such as arc discharges by the generalization of the theory resulting from a short mean free path compared with the gyroradius. The retrograde motion of cathode spots in the arc discharge is investigated through a model with the expanded formula of gyrocenter shift. It is found that a reversed electric field is formed in front of the cathode spots when they are under a magnetic field, and this reversed electric field generates a rotation of cathode spots opposite to the Amperian direction. The ion drift velocity profiles calculated from the model are in agreement with the experimental results as functions of magnetic flux density and gas pressure.     

Electrical conductance time constants for freely decaying arcs

Electrical conductance time constants for the early stages of free decay after current modulation have been calculated from experimental measurements on a 5 mm diameter cascade arc at atmospheric pressure. The time constants were found by measuring the electric field response of the asymptotic portion of the arc column immediately after a sudden step decrease of arc current. The electric field strength was monitored by means of the copper cooling disks of the cascade, whose probe characteristics were studied thoroughly. The initial high current was supplied by a capacitor discharge circuit which was inductively compensated to produce a square wave pulse of ～ 2 msec duration. Time constants for initial decay were measured in both argon and nitrogen for initial currents ranging from 100 to 400 amperes. The initial free decay time constants of nitrogen were found to increase weakly from approximately 25 to 35 usec over the initial current range considered. The time constants of argon decreased from approximately 100 to 60 Μsec over the same initial current range.     

高压热处理对铝青铜热物理性能的影响

在5 GPa压力下对铝青铜进行750℃、保温15 min的高压热处理,对高压热处理前后铝青铜的电导率以及25～600℃温度范围内的热扩散系数、热容和热导率进行测试,结合显微组织的观察结果,探讨了高压热处理对铝青铜热物理性能的影响。研究表明:高压热处理能增大铝青铜的热扩散系数,减小热容;对热导率而言,温度低于400℃时高压热处理能增大铝青铜的热导率,而温度高于400℃时高压热处理能减小铝青铜的热导率。分析认为,产生变化的主要原因是高压热处理使铝青铜的微观组织发生了变化。