Electrical Conductivity and Temperature Distribution of Arc Plasma in Narrow Insulating Channels

Having examined electrical conductivity and temperature distribution of a cross-section of an arc plasma column burning in the narrow channel between insulating walls. It was shown that arc pressure created by intrinsic magnetic field has little effect at subsonic velocity. In contrast with an open arc with convective cooling, mean electrical conductivity of an arc in a narrow channel is significantly dependent on the current passing through it.     

双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

脉冲电流作用下TIG电弧的数值分析

建立了脉冲电流下自由燃烧的TIG电弧的二维轴对称数学模型,利用FLUENT软件,通过选择合适的边界条件和强烈耦合控制方程组对脉冲TIG电弧进行了数值模拟,得到了在焊接电流周期性变化下电弧形态、电弧温度场、电弧轴线方向上的温度和速度及焊接工件表面电弧压力的变化情况;针对电弧压力,得到了不同峰值电流、占空比、脉冲频率作用下的分布情况,并分析了它们在脉冲电流作用下的周期性变化规律.分析结果表明:当脉冲电流发生突变时,它们的变化滞后于脉冲电流的变化,且从基值电流向峰值电流变化时的响应速度更快,并最终达到一个相对稳 关键词： 脉冲TIG焊 电弧 数值模拟 FLUENT     

Electromagnetic fields formed upon the interaction of ionizing radiation with matter

We propose a new approach to electromagnetic field calculations that involves the consecutive application of both quantum and classical electrodynamics methods. A current’s distribution is calculated via simulation modeling, using cross-section values obtained through quantum electrodynamics. The classical delayed potential of a current pulse of arbitrary form and duration, moving in a straight line at hyperlight velocity in the space-time representation, is calculated in an explicit form.     

基于光谱诊断的多丝熔化极气体保护焊电弧干扰分析

多丝熔化极气体保护焊中,由于电弧间的相互干扰,电弧工作状态不稳定,进而影响焊接过程稳定性和焊接质量。基于Boltzmann作图法测量电子温度场和Stark展宽法研究了多丝工作条件下电弧的电子温度分布和电子密度分布,结合高速摄影获得的定量化结果,给出电弧间干扰的定量化分析。光谱诊断结果表明双丝情况下,当加入电弧工作电流大于原电弧时,原电弧电子温度中心向新加入电弧稳定偏移,而且偏向新电弧一侧电子密度明显增加,而新电弧工作电流等于原电弧时,电弧电子温度和电子密度分布都反映出原电弧工作状态不稳定。三丝情况,由于加入第三根电弧,导致中间电弧电子温度分布变得复杂,而其电子密度分布接近于单丝工作情况。     

极性对自保护药芯焊丝电弧焊光谱特征的影响

由于自保护药芯焊丝具有抗风性以及优异的焊缝性能,已广泛应用于野外管道焊接以及大型机械的修复过程。电极极性是影响焊接过程的重要工艺参数。为了研究电极极性对电弧等离子体的影响机理,设计电弧等离子体空域中各点逐步扫描的同步采集系统,通过光谱特征谱线的分析,采用Stark谱线轮廓法计算电子密度,并且基于Boltzmann作图法计算电弧等离子体的温度,同时针对Al和Mg活性元素的分布特征进行分析。结果表明,靠近电极处,沿y轴负方向,直流正接时（焊丝接电源负极性）,弧柱中心区电弧电子密度、电弧温度和活性元素呈现“水滴状”分布。而直流反接时（焊丝接电源正极性）,弧柱中心区电弧电子密度、电弧温度和活性元素的分布特征表现为“手指状”分布。根据“自磁收缩”的原理,直流正接条件下,活性元素在径向方向受到的电磁力较小,整体分布呈现发散状。直流反接条件下,活性元素在径向方向受到的电磁力较大,收缩较为严重,整体表现为收缩状态。采用相同的电参数时,直流反接条件下弧柱中心区的电弧电子密度、电弧温度均大于直流正接条件下得到的电子密度和电弧温度,其中电子密度分布特征和带电粒子的电离程度是影响电弧温度的主要因素。在相同的电极极性下,随着电流、电压的增大,电弧等离子体的温度和电子密度都在显著增大。     

Investigations of the ignition of arc spots on cold cathodes in anoble gas atmosphere

To investigate the ignition of arc spots on cold cathodes under defined conditions, a special experimental setup was developed. An arc ignited between horn electrodes in a pure argon gas atmosphere is blown magnetically against a third so called commutation electrode, which is negatively biased against the arc plasma. The ignition of arc spots on this cathode was investigated by electrical measurements and high-speed photography. The arc traces of short current pulses were examined by in situ optical microscopy of the cathode surface. Two different modes of arc-spot ignition were observed: an initiation by a diffuse glow discharge, which may pass into a constricted arc spot, and an immediate formation of a constricted arc spot. The two modes of arc-spot ignition at atmospheric pressure were attributed to different surface structures, which are characterized by broad or narrow distributions of local ion current density enhancement factors. Ion current density enhancement may raise the field strength and temperature on the tips of microprotrusions so far that they emit electrons. A sufficiently high density of small emission sites produces locally such a high average current density that a plasma channel and an arc spot on the cathode surface arc formed. With lower pressure, the influence of the surface structure is reduced and pushed back by Townsend-γ emission     

微束等离子体弧焊电弧物理特性多场耦合分析

根据磁流体动力学方程组，建立了微束等离子电弧模型，使用有限元分析软件COMSOL进行模拟计算。结果表明，电弧中心温度分布从钨针至焊件整体呈“毛笔”状，其中，喷嘴下方电弧形态呈“钟罩”形，在焊件上温度分布符合高斯分布特征；电弧等离子体在喷嘴内部速度较大，离开喷嘴后，其方向由喷嘴内的竖直向下逐渐变为到达工件时的向四周扩散；电流由焊件表面流出，经过弧柱区域流入钨针下端面，在钨针下端面附近取得最大值；电弧磁通密度分布呈“肺叶”状。最后进行了相应的熔焊试验，试验过程中拍摄的电弧轮廓与仿真电弧形态基本一致。     

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.     

Influence of residual gases on cathode spot behavior

A residual gas in a vacuum arc chamber influences the behavior of the arc by two effects: it changes the state of the cathode surface, in particular the surface cleanness, and it influences the interelectrode plasma. Experiments are summarized dealing with the influence of the residual gas on the arc parameters in a pressure range of 10^-6-10^-5 Pa. With increasing pressure, general tendencies are a decrease in the fluctuations of the burning voltage, in the chopping current, and in the current density, and an increase in the arc lifetime, spot velocity, and spot diameter. The conditions at the cathode surface are decisive for the spot behavior and not the pressure. Surface contaminations render the arc more stable. The transition between the so-called cathode spot type 1 (on contaminated surfaces) and type 2 (on clean surfaces) was found to be smooth rather than abrupt     

熔池表面形状对电弧电流密度分布的影响

电弧电流密度分布决定着电弧热流密度、电弧压力的分布,是了解焊接电弧物理本质,建立 焊接过程数学模型的基础.根据电弧物理的基本原理,建立了电弧电流密度在变形熔池表面 上的分布模型,定量分析了熔池表面形状对电流密度分布的影响规律.计算表明,电流密度 在电弧中心线附近呈双峰分布,在离开电弧中心线一定距离处变为单峰分布,熔池表面形状 对电流密度分布有明显的影响.基于该模型计算的焊缝几何形状与实测结果符合得较好. 关键词： 熔池表面变形 电流密度 分布模型     

Plasma expansion and current flow in a vacuum arc with a smallanode

A low-density plasma flow in a vacuum arc with a small anode, which intercepts only part of the cathodic plasma jet, was studied theoretically using a two-dimensional approximation. The plasma expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the plasma was determined by a self-consistent solution of the gasdynamic and electrical current equations. Magnetic forces from the azimuthal self-magnetic field were taken into account. The influence of the ratio of the anode radius to initial plasma jet radius on the plasma density, velocity, current distribution, and anode sheath potential drop is analyzed. It is shown that the mass and current flow in a 500 A arc are compressed near the axis. This leads to an increase in the plasma density by a factor of two and in the axial current density by a factor of 1.5     

Analysis of Cross-Flow Arcs in Transverse Magnetic Fields

Through the specification of two independent variables (e. g., arc current and mainstream velocity), and using appropriate phenomenological relations, the flow fields, temperature fields, and arc boundary shapes of magnetically balanced cross-flow arcs have been determined. Flow through the arc occurs at lower Reynolds numbers, Reo ~ 1; at higher Reynolds numbers a dividing streamline is formed, inside of which double vortex flow is found. Isotherms are nearly circular for the case of flow through the arc. At the higher Reynolds numbers the isotherms are non-circular throughout the cross-section with major axis transverse to the direction of flow.     

A rotating arc gas pump for circuit breaking and other applications

A rotating arc circuit breaker is described which uses an auxiliary current source to generate the magnetic field for driving the arc. Test results obtained using optical fiber measurement systems have shown that there are three main arcing phases. Initially the arc rotates at an essentially constant but low velocity, subsequently its velocity oscillates between this and much higher values, and finally the are plasma may become diffuse in nature. Test results obtained with dielectric strength probes have indicated that a unidirectional flow of arc heated gas is generated. The flow is away from the moving contact of the interrupter so promoting good dielectric strength in this critical contact region. The combination of the optical fiber and dielectric probe results indicates two possible modes of gas pumping represented, respectively, by a fan and a piston-type action of the arc. Simplified analytical models for both modes are developed with predictions obtained showing good agreement with the experimental results. Discussion of experimental results suggests that the transition from oscillatory velocity changes to diffuse arcing represents an important parameter for scaling the geometries of future interrupters and arc heaters     

带状真空电弧磁过滤器等离子体分布特性及制备类金刚石膜研究

采用大尺寸矩形石墨靶作为真空阴极电弧源, 研制了带状真空电弧磁过滤器. 使用法拉第杯和朗缪尔探针对90 ℃弯曲磁过滤器中的带状等离子体出口所在平面的15个区域的离子能量和密度进行了测试; 用该带状真空电弧磁过滤器制备了类金刚石膜(diamond-like carbon, DLC); 对相应位置上的类金刚石膜进行了Raman分析和膜厚测量. 结果表明: 磁过滤器出口所在平面的15个划分区域中离子能量分布接近麦克斯韦分布, 离子能量分布与类金刚石膜的结构具有明显的对应特征, 离子密度分布与DLC膜膜厚分布相互之间具有相关性.     

Existence regions of regimes with anomalously high rates of plasma generation in grid plasma switch elements

Results are presented from a systematic investigation of the conditions under which anomalously high rates of plasma generation are observed in the anode region of a low-voltage Knudsen arc in grid plasma switch elements. The phenomenon develops over a wide range of currents and switched voltages under conditions for which the plasma density in the cathode-grid region is noticeably higher than the density in the anode region. and its onset is characterized by a pronounced pressure threshold of ∼2×10⁻² Torr. The results are analyzed from the standpoint of the possible mechanisms for anomalous plasma generation — collisional nonresonance diffusion of electrons in velocity space, leading to enrichment of the distribution function in fast particles, and the collapse of Langmuir waves in the gap at the high energies of the beam produced when the wires of the grid are bridged by the quenching pulse and and the current is blocked. Zh. Tekh. Fiz. 67, 15–21 (June 1997)     

Plane hydroelastic beam vibrations due to uniformly moving one axle vehicle

The hydroelastic vibrations of a beam with rectangular cross-section is analyzed under the effect of an uniformly moving single axle vehicle using modal analysis and two-dimensional potential flow theory of the fluid neglecting the effect of surface waves aside the beam. For the special case of homogeneous beam resting on the surface of a water filled prismatic basin, the normal modes are determined considering surface waves in beam direction under the condition of compensating the volume of the enclosed fluid. The way to determine the vertical acceleration of the single axle vehicle is shown, which governs the response of the system. As analysis results the course of wheel load, the surface waves along the beam and the flow velocity distribution of the fluid is demonstrated for a continuous floating bridge under the passage of a rolling mass moving with uniform speed.     

Arc motion in railgun plasma armatures

H.H. Maecker's theory (1971) for arc motion and displacement is extended to the pressure-dependent arc conditions found in railgun armatures. It is shown that for the railgun plasma armature there are thermal mechanisms, which do not exist for solid armatures, that tend to move the peak of the current density forward toward the base of the projectile, thereby mitigating the tendency of the velocity skin effect to concentrate the current density toward the rear. This effect may explain the variance between some theoretically predicted current density profiles in plasma armatures and those measured by B-dot probes     

Statistical Theory of Two-Sided Multipactor

We develop a statistical theory of secondary-emission discharge (SED) taking the energy distribution of secondary electrons into account. The theory allows one to describe quantitatively the initial stage of development of a two-sided multipactor. For an arbitrary probability density of normal components of the ejection velocity and an arbitrary distance between the walls enclosing the microwave discharge plasma, we construct an analytical solution for the electron distribution function over transit times. The performed analysis is based on the results of a detailed study of conditions under which an electron reaches the opposite side. With allowance for the spread in thermal velocities, we derive a recurrence relation between the electron distribution functions over emission phases and formulate a general integral equation from which the resulting stationary distribution and the threshold of SED onset are determined.