Vortex Flows Induced by Electric Arc

In this paper a mathematical model of the stationary electric arc is made on the basis of solution of radiation gas dynamics two-dimensional equations. Numerical analysis of electric arc with small length, depending on current force, distance between electrodes, electrode behaviour and geometry, type and expenditure amount of plasma forming gas, is carried out. It is shown that under some definite conditions electric arc induces toroidal gas vortexes playing an important part in the process of heat and mass transfer in electric arc plasma.     

Processes and properties of electric arc stabilized by water vortex

Experimental investigation of an electric arc stabilized by a water vortex was carried out in a DC arc plasma torch for the power range 90-200 kW. Volt-ampere characteristics of the arc as well as the power balance were determined separately for the part of the arc column stabilized by water and for the remaining part between the nozzle exit and the external anode. The temperature of arc plasma close to the nozzle exit was determined by emission spectroscopy. Negatively biased electric probes in the ion collecting regime were used for determination of the plasma flow velocity. The measured temperatures up to 27000 K, and velocities up to 7 km/s are higher than the values commonly reported for plasma torches with DC arcs stabilized by a gas flow. Mass and energy balances within the arc chamber were determined from the experimental results. The radial transport of the energy by radiation was identified as a decisive process controlling the arc and plasma properties. The balance of radial energy transport was studied. The ratio of energy spent for evaporation of the water to the energy absorbed in the evaporated mass is very low in the water stabilized arc. This is the principal cause of high plasma temperatures and velocities found by the measurements     

On the application of the theory of Lorentzian plasma to calculation of transport properties of multicomponent arc plasmas

The application of the Lorentzian plasma theory for the calculation of the properties of multicomponent electric arc plasma is considered. It is shown that this model gives satisfactory results in the temperature range, which is corresponding to the weakly ionized arc plasma and arc plasma with dominant first ionization. The calculations are provided for the arc plasmas of noble gases and their mixtures between them and also that with metals. It is also pointed that the discrepancy between the electron temperature and gas temperature can be significant even at relatively weak electric fields, that fact must be taken into account under the simulation of arc discharges.     

Analysis of plasma characteristics and conductive mechanism of laser assisted pulsed arc welding

This study aims to investigate the arc plasma shape and the spectral characteristics during the laser assisted pulsed arc welding process. The arc plasma shape was synchronously observed using a high speed camera, and the emission spectrum of plasma was obtained by spectrometer. The well-known Boltzmann plot method and Stark broadening were used to calculate the electron temperature and density respectively. The conductive mechanism of arc ignition in laser assisted arc hybrid welding was investigated, and it was found that the plasma current moved to the arc anode under the action of electric field. Thus, a significant parabolic channel was formed between the keyhole and the wire tip. This channel became the main method of energy transformation between the arc and the molten pool. The calculation results of plasma resistivity show that the laser plasma has low resistivity as the starting point of conductive channel formation. When the laser pulse duration increases, the intensity of the plasma radiation spectrum and the plasma electron density will increase, and the electron temperature will decrease.     

Effect of Laser Pulse on Arc Plasma and Magnesium Target in Low-Power Laser/Arc Hybrid Welding

Low-power laser/arc hybrid welding process of magnesium alloy shows that the weld capability of tungsten-inert-gas arc is improved under the action of laser pulses. The effect of laser pulse on arc plasma is analyzed by studying the plasma spectra, plasma shapes, and arc voltage in this paper. On the one hand, laser pulse attracts arc plasma to laser keyhole and improves the stability of arc plasma; on the other hand, laser pulse expands the arc plasma and concentrates the electric conducting route of arc plasma. All these increase the output power and energy density of arc plasma, so the welding penetration is improved. In addition, laser pulses are controlled to act on the negative wave of alternating-current arc (the target metal has negative polarity) in hybrid welding process to improve the stability of arc plasma and weld penetration.      

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     

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     

滑动弧低温等离子体放电特性的数值模拟研究

滑动弧等离子体的电弧温度场、电场和导电区域尺寸是确定电子温度、电子密度、化学反应速率以及能量效率的重要参数.对气流量为1.43 L/min和6.42 L/min时50 Hz交流滑动弧放电的电参数进行了测量;用瞬态的电弧模型描述滑动弧的能量传递,并用近似的介质电导率和热扩散系数对模型进行简化,解决了由于电弧结构变化所导致的移动边界问题;模拟求得等离子体的电弧结构、电场强度和动态温度场等参数的演化.其中,电弧电场的模拟值与实验值基本符合,计算得到电弧轴心温度可以达到5700—6700 K.研究结果表明,气流直 关键词： 滑动弧等离子体 温度场 电场强度 导电半径     

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     

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.     

光电偶效应和光束整形对激光稳定气体保护焊接的增益

为了开发和改进激光诱导稳定焊接加工技术,需要通过激光辐射使电弧的导电率达到最大值。光电偶效应是控制该过程的主导因素,该过程的优化将会保证电弧的稳定性。光电偶效应提高了等离子体粒子电离的概率,从而提高了电弧的导电率。激光光子和氩原子之间的电子-原子碰撞相互作用产生了带电粒子。电离率越高,电弧的导电率就越高。为了充分利用光电偶效应,我们还应考虑工件上的光束焦点位置、光束形状和激光波长因素。     

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研究了滑动弧放电过程中电参数的变化,并对滑动弧等离子体中的非平衡度和各个参数之间的关系进行了讨论。应用双通道电弧模型,对电弧在气流作用下运动规律进行了数值模拟,模拟所得的结果有助于分析滑动弧非平衡等离子体的产生机理。     

Stabilization of Long Electric Arcs by Rotating Magnetic Fields of Different Configurations

The results of the investigation of the direct current electric arc under the influence on it of the rotating magnetic fields of the inductors with a different number of poles pairs are given in the article. The analysis and the comparison of the arc energetic characteristics and of its movement parameters in the rotating magnetic fields of different configurations were carried out. The comparison of the experimental data and of the results of the theoretical analysis of the arc movement in the 2-poles and 4-poles inductors fields was carried out. A number of original methods for the application of the researched type of the magnetic effect on the electric discharge in plasma techniques and technology was suggested.     

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.     

Emission Intensity Enhancement of DC Arc Plasma Induced by External Oscillating Magnetic Field

Direct current (dc) arc plasma with continuous aerosol supply was coupled with an external oscillatingmagnetic field of a few tens of mT and a frequency of up to 1 kHz. Such configuration was used to alter the plasma‐related radiative properties. The magnetic field was oriented perpendicularly to the electric field in the plasma and forced the arc column to oscillate as a whole with respect to the surrounding atmosphere. The magnitude of the appliedmagnetic.eld controls the amplitude of the oscillatory motion. Several parameters that can contribute to the radiative properties of the plasma were investigated (arc current, composition of aerosol introduced into the plasma, amplitude and frequency of the magnetic field applied). Spectral emission from different zones of the plasma column was measured by optical emission spectroscopy (OES). In comparison to steady‐state plasma, the applied magnetic field induces an intensity enhancement of emission of the most analytes considered. The intensity enhancement is strongly affected by the amplitude and frequency of plasma column oscillations, i.e. by plasma column velocity. Also, intensity enhancement depends on the plasma zone observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Der Einfluß einer radialen Masseneinströmung auf elektrische Lichtbögen

In this paper the influence of a radial instreaming gas on electric arcs is investigated. An axial or an azimuthal mass flow may be superimposed to the radial one. Using the basic equations of the single-fluid model of plasma physics the important properties and parameter dependences are numerically calculated and discussed. The results are compared with those of a corresponding arc without an instreaming radial mass flow. Using an arc heater with radial mass flow it is possible to reach much higher axis temperatures and enthalpy densities. Choosing a set of well selected working conditions nearly the whole electric input may be transformed into axial enthalpy flux of the gas to be heated. The paper illustrates the mutual interaction between the dynamic and thermic functions of an electric arc.     

Electric arc plasmatorch for steam heating

A construction arrangement of electric arc plasmatorch with copper tubular electrodes for steam plasma generation was developed and tested. Experimental data on energy curves of this plasmatorch with nominal power of 100 kW are presented.     

Computation of steady flow in the molten pool at electric-arc heating

Peculiarities of the formation of melt hydrodynamics in the molten pool of electric arc as a result of a viscous interaction with the arc plasma flow and the effect of electromagnetic forces are considered. It is shown that in a relatively shallow pool, the role of viscous interaction with plasma flow predominates electromagnetic forces. In a deeper pool, the flow in peripheral upper region is formed as before by a viscous interaction between plasma and melt, and the electromagnetic forces dominate in deep regions.     

Schnell rotierender Lichtbogen als spektroskopische Lichtquelle

An electric arc quickly moved magnetically forms a closed plasma cone or plasma ring between two concentrically arranged electrodes. Aerosols and suspended matters can be brought into the plasma in an optimum manner with a little carrier gas flow, and can be excited to emission. The dates applied and attained till now are: Arc current 5…?20 A, magnetic field strength 10⁴…?4 · 10⁵ A/m, magnetic induction 0.1…?0.3 T, rotation frequency 8…?15 kc, carrier gas air or argon maximum flow 0.5 1/min, intensity increase for CuI-lines up to factor 100. Further applications are possible for special lamps and electric arc diagnostics.