Experiments on Arc Perturbation in Turbulent Gas Flow

Electric arcs burning in a strong, turbulent, axial nitrogen gas flow are studied. Time-resolving (framing) picture series of the arc and its deformations are taken through the quartz tube channel wall. Individual perturbations like kinks exist under strong, turbulent flow conditions. They move with constant acceleration in the direction of the cold gas flow. The temperature of the arc core is disturbed at the position of these disturbances, too. This shows up most distinctly, if the decay of the arc after short-circuiting is studied, as has been done additionally.     

Calculation of thermal and spatial characteristics of a longitudinally blown arc

A method is proposed for calculating the thermal and spatial characteristics of the column of an electric arc in the channel of a plasmatron for a given set of averaged electrical and gas dynamical parameters. The method is based on the channel model of a longitudinally blown arc. For given discharge parameters (current intensity in the discharge, power input into the discharge, mean pump rate of the gas through the plasmatron) the method permits quite accurate determination of the temperature in the current conducting channel of the discharge arc, the radius of the channel, and distribution of the temperature fields in the nonconducting zone (heat transfer zone) as a function of the longitudinal flow coordinate z downstream. The results may be used in modeling and engineering calculations for determining the most efficient conditions for heating a gas by pumping through the channel of an arc plasmatron.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 76–82, August, 1991.     

空心针板放电等离子体气体温度和振动温度研究

使用空心针板放电装置,以氩气作为导入气体,在大气环境下产生了1.6~3 cm波长的等离子体炬。利用发射光谱法,研究了等离子体炬弧根和弧梢处的气体温度和振动温度,以及它们随气体流量的变化。等离子体气体温度通过对OH基309 nm附近的谱带进行拟合得到,等离子体振动温度由氮分子第二正带系C3Πu—B3Πg计算得到。实验发现弧根和弧梢处的气体温度相等,并随着气体流量的增大而下降。当气体流量从3.0 mL.min-1增大到6.5 mL.min-1时,气体温度由350 K下降到300 K。当气体流量较小(如3.0 mL.min-1)时,弧梢处的振动温度(1 950 K)高于弧根处的振动温度(1 755 K)。随着气体流量的增大,弧梢处与弧根处的振动温度均下降,但弧梢处下降速率较快。当气体流量较大时,二者趋于相等。     

Axially blown SF6-arcs around current zero

The increase of the interrupting capability of modern SF6 puffer breakers demands a better knowledge of the interaction of the arc with the gas flow. During the current interruption in an SF6 breaker the arc temperature in the stagnation zone is of decisive importance. The temporal evolution of the arc temperature and the diameter is studied by means of interferometry and emission spectroscopy. Experimental results are presented which show the influence of the current slope and the gas pressure on the arc decay. These results are compared with a theoretical model describing the temperature decay after current interruption.     

Study of a circuit-breaker arc with self-generated flow. II. Theflow phase

For pt.I see ibid., vol.16, no.6, p.606-14 (1988). The experimental results presented concern the variations of the mean electric field and gas mass flow during this phase. The most important part consists of a modeling of the evolution of the interruption arc during the decrease of the current from 1000 A to 0. In this modeling, based on the conservation equations of mass and energy, the boundary conditions are determined by an approximate separate modeling of the arc whereas turbulence is treated through Prandtl's approximation. This theoretical study has been developed in the case of SF₆ and nitrogen. The computed values of the electric field and temperature show that the arc has a quasi-stationary behaviour as long as the current intensity is greater than a few tens of amperes, for a decay rate of 1.35 A/μs. The energy losses are governed by radiation at high current and by turbulence conduction at low current. The most important results concern the conductance, whose evolution time constant, immediately prior to current zero, is 3.5 μs in SF₆ and 15 μs in nitrogen. The difference is essentially due to variations with temperature of thermal conductivity and specific heat in two gases     

基于0级数据的星载大气痕量气体差分吸收光谱仪在轨衰变监测

大气痕量气体差分吸收光谱仪(EM I)是一种紫外可见成像光谱仪,主要用于实现高空间分辨率的全球每日大气痕量气体浓度反演.EM I在轨运行期间,受空间环境影响,元器件性能随时间推移会不断衰变.为有效监测其衰变状况,利用载荷对地各轨0级数据解析出在轨温度,实现长期在轨温度监测;通过计算各轨道星下点黑暗时的暗背景图像噪声的均...     

闪电消散过程等离子体温度衰减规律的理论研究

利用流体运动方程、连续性方程和能量守恒方程,对自然闪电回击后的消散过程建立数学模型,计算了等离子体温度随时间和空间的变化规律.结果分析表明：在相同的通道半径处,前期温度随时间衰减较快,后期较慢,并且,初始温度越高,衰减越快;随着半径的增大,温度的衰减幅度逐渐减小.同一时刻,半径小的位置温度梯度较小,半径大的位置温度梯度较大.由衰减到NO冻结温度的时间和位置,初步推断氮氧化物（NO_x）生成主要在闪电冲击波之后50 ms内、半径R=9 mm的等离子体通道内. 关键词： 闪电消散过程 等离子体 温度     

小功率等离子体射流的流特性

采用焓探针对小功率(5kW)热喷涂等离子体射流的焓、温度和速度进行了测量和计算。研究了气体成分、流量、电弧电压和电流对等离子流体的焓、温度和速度分布的影响。结果表明,对于单一氩气等离子体,当使用新喷嘴时,增大氩气流量能够使喷嘴内部电弧弧根向出口方向移动,从而增加等离子体射流的焓、温度和速度。对于Ar-N2等离子体,增加气体中氮气的含量,会提高等离子电弧电压,在同样的输入功率下,改变等离子电流和电压对等离子体的焓、温度和速度影响较小。对于Ar-N2等离子体,增加氢气含量会明显地提高等离子射流的速度和热传递。     

Observation of arc modes in a magnetically rotating arc plasma generator

An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry.     

Laser interferometric measurements of electron density in an arc plasma

The paper describes the application of a laser interferometric technique to arc discharges operating at atmospheric pressure. The limitations of this method are discussed in detail. Results are given for the axial electron density in an argon arc, tube 5 mm diameter, over a current range 30–75 A. In addition the decay of the electron density following rapid arc interruption is also given. It is shown that the time constant of the conductance decay which can be derived from the preceeding measurements is in very good agreement with experimental values determined directly.     

Production of a large area diffuse arc plasma with multiple cathode

An arc channel at atmospheric pressure tends to shrink generally. In this paper, a non-transferred DC arc plasma device with multiple cathode is introduced to produce a large area arc plasma at atmospheric pressure. This device is comprised of a 42-mm diameter tubular chamber, multiple cathode which is radially inserted into the chamber, and a tungsten anode with a nozzle in its center. In argon/helium atmosphere, a large area and circumferential homogenous diffuse arc plasma, which fills the entire cross section surrounded by the cathode tips, is observed. Results show that the uniformity and stability of diffuse arc plasma are strongly related to the plasma forming gas. Based on these experimental results, an explanation to the arc diffusion is suggested. Moreover, the electron excitation temperature and electron density measured in diffuse helium plasma are much lower than those of constricted arc column, which indicates the diffuse helium plasma probably deviates from the local thermodynamic equilibrium state. Unlike the common non-transferred arc plasma devices, this device can provide a condition for axial-fed feedstock particles. The plasma device is attempted to spheroidize alumina powders by using the central axis to send the powder. Results show that the powder produced is usually a typical hollow sphere.     

Numerical Analysis of Alternating Current Arcs

Solutions of the coupled, non-linear, two-dimensional, non-steady equations of continuity, momentum, and energy have been obtained for an alternating current argon arc located in a constant diameter channel of a converging nozzle configuration. Real gas properties, radiation, convection, viscous dissipation, and turbulence effects were incorporated in the analysis. Spatial and timewise distributions determined included the flow, temperature, and pressure fields, dynamic arc radius, and arc resistance gradient.     

Self-Similar Gas Motion Near The Evaporating Electrode of An Electric Arc

Simple solutions of 1Dt gas-dynamical equations based on similarity analysis are possible for the gas surrounding a point source of mass and energy such as an electrode (cathode) arc spot. To obtain nontrivial (non-zero temperature) solutions throughout, two-scale formulation is used that permits an additional boundary condition near the source. Three generalised gas flow variables, R, Z and V, related to gas density, temperature and velocity are calculated and presented as functions of a single similarity parameter, λ, related to position and time. The computational results are compared with data from two gas discharge experiments: on gas disturbances due to an electric arc of micrometer length in atmospheric air and on expansion of a metal-vapour plasma cloud generated by a low-pressure cold-cathode arc.     

Evolution of magnetically rotating arc into large area arc plasma

An arc channel tends to shrink due to its conductivity increasing with the increase of temperature.In this study,to generate large area arc plasma,we construct a magnetically rotating arc plasma generator,which mainly consists of a lanthanide tungsten cathode(13 mm in diameter),a concentric cylindrical graphite anode chamber(60 mm in diameter)and a solenoid coil for producing an axial magnet field.By controlling the cold gas flow,the magnetically rotating arc evolves from constricted mode to diffuse mode,which almost fills the whole arc chamber cross section.Results show that the diffuse arc plasma has better uniformity and stability.The formation mechanism of large area arc plasma is discussed in this paper.     

Prediction of gas tungsten arc welding properties in mixtures ofargon and hydrogen

A theory of gas tungsten arc welding (GTAW) arcs that treats the tungsten electrode, the arc, and the workpiece as a unified system has been applied to make predictions in two dimensions of the temperature distributions in the arc, the tungsten cathode, and the workpiece, for any given arc current and gas mixture. Predictions of arc temperatures, radii, and voltages are compared for argon and mixtures of argon and hydrogen. It is found that arcs in gas mixtures containing hydrogen are more constricted and have a higher maximum temperature and arc voltage than arcs in pure argon. The addition of hydrogen also significantly increases the volume of molten material in the weld pool due to the higher thermal conductivity of argon-hydrogen mixtures at temperatures at which molecules of hydrogen dissociate. Predictions are also compared for workpieces of steel and aluminum. The volume of molten material is very much less for aluminum, despite its lower melting point, because of the higher thermal conductivity of aluminum. Predicted arc voltages as a function of current for a mixture of 10% hydrogen in argon are in good agreement with experimental results     

On the temperature dependence of the phosphorescence of CaF2 : Mn phosphor in different atmospheres

The temperature dependence inthe region of 24–150°C of the phosphorescence of CaF₂ : Mn phosphor in the atmospheres of nitrogen gas, vacuum and moisture-saturated air were studied. A decay formula was found to adequately describe the rate of decay of the trapped electrons — which is assumed to be proportional to the amount of phosphorescence observed — in thermal traps. In nitrogen gas and vacuum the decay constants of the trapped electrons are dependent only on the storage temperature and not on the storage atmosphere of the phosphor. A slight effect of water on the rate of decay of the trapped electrons was also observed.     

高压火花隙开关中气体冷却的数值模拟

 高温气体的冷却对火花隙开关的重复运行具有重要的影响。利用流体方程、热传导方程和理想气体状态方程构建的方程组,对火花隙开关中高温气体冷却的过程进行了数值模拟。分析了气体导热系数、粘性系数、对流及气体压强等要素对气体冷却速度的影响,得到了气体冷却的基本规律：火花隙开关内气体的冷却以传导为主;若不采用其他手段,气体在十几ms内冷却较困难;对流的作用经数十ms后才显著;气体的粘性系数对气体冷却的影响可以忽略。可以通过选用导热系数高的气体,优化电极结构或采用吹气方法提高气体冷却速度的办法。     

The effects of a temperature dependent thermal diffusivity and radiation loss on arc column decay

Numerical computations of the free recovery of arc columns in air and nitrogen are presented. In addition to thermal conduction radiation losses are taken into account and the influence of a temperature dependent thermal diffusivity is considered. At short times after interruption a high thermal diffusivity in the core accelerates the conductance decay while at later times the rate of recovery is reduced due to a small diffusivity in the outer regions of the column. For high current arcs radiation is an important loss mechanism immediately after an interruption.     

Physical Processes in Gas-Tungsten Arcs

Experiments designed to validate a two-dimensional theoretical model of a gas-tungsten arc welding (GTAW) arc are described. The predicted temperature distributions agree well with the measured values in the body of the arc. Agreement between theory and experiment near the electrodes has been impoved by the new boundary conditions in the theory. Experimental determinations of the effects of gas flow rate, electrode stick-out distance, and nozzle diameter on the temperature of GTAW arcs are discussed. A theoretical investigation of an addition of 0.1-percent cerium to an argon arc shows that enhanced low-temperature conductivity and extra radiative cooling due to cerium can lead to marked changes in arc properties.     

Dynamic behaviour of electric arc gas discharge

The time-dependent energy and circuit equations are solved numerically to obtain temperature profiles, current-voltage characteristics and electric field strength vs axial temperature diagrams in the asymptotic region of a wall-stabilized electric arc operated in nitrogen. Dynamic current-voltage characteristics and transient phenomena of the formation of the stationary state during the spark ignition phase are studied. The arc timeconstant for free decay is computed and compared with approximate analytical results. It is found that for fixed initial conditions the arc response to the variable applied voltage is several times longer than the arc time-constant for free decay.The author is grateful to Dr. Z. Sedláek, Dr. M. Hrabovský and Dr. R. Klíma for their stimulating advices and helpful comments.