Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology. In this paper, a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc. The temperature, total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials. It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column. As the arc current increases from 100 A to 200 A, the total anode heat flux increases, however, the maximum electron condensation heat flux decreases due to the arc expansion. The anode materials have a significant effect on the temperature and heat flux distributions in the anode region. The total heat flux on thoriated tungsten anode is lower than that on copper anode, while the maximum temperature is higher. The power transferred to thoriated tungsten anode, ranked in descending order, is heat flux from heavy-species, electron condensation heat, heat flux from electrons and ion recombination heat. However, the electron condensation heat makes the largest contribution for power transferred to copper anode.     

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。     

导热系数测定过程中下铜板散热速率的理论计算

采用传热学的相关理论,对稳态法测量导热系数实验过程中下铜板的散热速率进行了计算,并与实测结果进行对比分析。     

航天器变速热泵回路的技术优势分析

在保证航天器废热排放量的基础上,通过计算对比分析了固定转速热泵回路热控系统和变速热泵回路热控系统的耗电量,结果证明后者比前者节能20％左右。综合分析还表明:变速热泵可以实现软启动,对航天器上的电网无冲击,对其它用电设备无干扰;可以实现快速制冷和供热;控温精度高,回舱流体温度波动小;可靠性高,寿命长;脉动噪声小;可以实现无级调速,具有热负荷调节范围宽等技术优势。变速热泵技术已经发展成熟,具备了在航天器上应用的条件。     

An investigation on capability of hybrid Nd:YAG laser-TIG welding technology for AA2198 Al-Li alloy

This paper surveys the capability of the hybrid laser-arc welding in comparison with lone laser welding for AA2198 aluminum alloy experimentally. In the present research, a continuous Nd:YAG laser with a maximum power of 2000 W and a 350 A electric arc were used as two combined welding heat sources. In addition to the lone laser welding experiments, two strategies were examined for hybrid welding; the first one was low laser power (100 W) accompanied by high arc energy, and the second one was high laser power (2000 W) with low arc energy. Welding speed and arc current varied in the experiments. The influence of heat input on weld pool geometry was surveyed. The macrosection, microhardness profile and microstructure of the welded joints were studied and compared. The results indicated that in lone laser welding, conduction mode occurred and keyhole was not formed even in low welding speeds and thus the penetration depth was so low. It was also found that the second approach (high laser power accompanied with low arc energy) is superior to the first one (low laser power accompanied with high arc energy) in hybrid laser-arc welding of Al2198, since lower heat input was needed for full penetration weld and as a result a smaller HAZ was created.     

Heat Transfer in Electric Arc Chamber of Linear Plasmatron

Classification and performance capability of electric are linear plasmatrons are presented. The results of investigation into convective and radiative heat transfer in the discharge channel of a plasmatron are reported. The radiative heat transfer dominates both in the structure of heat losses and in the formation of discharge volt-ampere characteristic at the initial region of the flow. Relations to calculate heat losses by radiation are given. Radiative convective interaction at the arc boundary is shown to play a substantial role for high-current discharges stabilized by axial vortex gas flow. It is shown that the calculation of convective heat transfer at the turbulent region of the flow may be carried out by flow averaged parameters.     

Modeling and Measurement of the Initial Anode Heat Fluxes in Pulsed High-Current Arcs

An anode heat flux model has been developed for pulsed high-intensity dc arcs. The model is based on temperature-time-history measurements of the rear face of a very thin plane anode and high-speed streak photographs of the arc. The arc heat flux model is derived from a comparison of experimental data with an analytical solution of the one-dimensional heat conduction equation and the arc intensity and timing information obtained from high-speed photographs. A simplified input heat flux model consisting of connected segments of linearly varying heat fluxes with respect to time is used. Duration of the individual segments is determined from the streak photographs and the graphical match of measured rear-face temperature history and the numerical solution. Results using argon gas at atmospheric pressure indicate an initial transient heat flux regime of 100-?s duration with a peak heat flux of 2 × 109 W/m2 followed by a quasi-steady heat flux regime with a heat flux of 1 × 108 W/m2.     

双面电弧焊接的传热模型

将等离子焊接(PAW)电弧和钨极氩弧焊(TIG)电弧串接,相对作用于工件的正反面形成双面电弧焊接(DSAW)系统,可以引导焊接电流沿工件厚度方向流过小孔,补偿等离子电弧穿透工件时消耗的能量,以有效地提高等离子弧的穿透能力.综合考虑影响双面电弧焊接正反面熔池几何形状的力学因素,建立了熔池表面变形的控制方程,以此为基础并采用帖体曲线坐标系建立了DSAW焊接传热的数学模型,分析了DSAW,PAW焊接传热的差异,从传热的角度解释了DSAW焊接熔深增加的原因.焊接工艺实验表明,计算结果与实测结果吻合良好. 关键词： 双面电弧焊接(DSAW) 传热模型 熔池表面变形模型     

氩孤钎焊加热区比热流分布的动态分析

通过对不同弧长、不同电流氩弧的高速摄影拍摄以及利用影片数据分析处理系统对其动态过程的研究,发现用高斯函数模拟氩弧钎焊加热区的比热流q(r)分布特性时,理论计算值与测量值符合得较好.实验结果表明,氩弧钎焊时采用大电流的焊接规范既不经济亦无必要.因为,由q(r)分布模型可知,当弧长不变增加焊接电流时,氩弧钎焊加热区半径变小,而q_m急剧增大,往往诱发液态钎料过热,毛细填充作用不强等问题,使钎焊质量下降;当焊接电流不变增加弧长时,加热区半径显着增大,q_m减小,反而有利于保证氩弧钎焊质量和生产效率.     

Magnetic Field Effect on the Volt‐Equivalent of Arc Spot Heat Flux

The results of an experimental study of the arc spot heat flux on the copper cathode of a coaxial Electric Arc Heaters (EAH), with magnetically driven arc, in air are presented. The three rings method was used for indirect separation of arc spot heat flux from total heat entering the electrode. As a result of joint generalizing new and previously published data, the linear dependence of the volt equivalent of arc spot heat flux on magnetic field was obtained for the range B = 0.01 – 1 Tesla and atmospheric pressure. A method, which allows to improve the measurement of the volt equivalent in highly unsteady arc spots, is proposed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

吸附式制冷系统回热过程对系统性能的影响

在吸附式制冷系统中,回热过程起到了重要作用。理论上可回收的热量很多,实际上,由于吸附床传热系数的限制,使得回热量大大减少。同时长时间回热也减慢了吸附床的升降温速率,影响了系统运行的制冷量和能效比。本文通过对计算数据和实验数据的分析,确定了回热过程及回热时间对系统性能的影响。     

含氢电极真空弧放电等离子体时空分布特性研究

真空弧离子源在真空镀膜、材料表面改性、真空大电流开关、加速器离子注入等领域有广泛应用,目前国内外对真空弧放电等离子体的研究主要针对纯金属或合金电极,对含氢电极的研究和公开报道较少.本文利用高时空分辨的四分幅图像诊断系统,结合氢和钛原子特征线单色器件,研究了含氢钛电极的真空弧微秒级脉冲放电等离子体的轴向和径向时空分布特性.研究表明:在真空击穿阶段,阳极区域发光更为明显,阳极电极解吸附释放的氢原子是引发击穿的主要放电介质;在真空弧阶段,阴极-绝缘-真空三结合点处产生圆锥状阴极斑,喷射出大量的等离子体以维持弧放电,同时电极内壁非阴极斑区域也有少量等离子体产生,等离子体中H原子的轴向和径向空间分布均比Ti原子均匀.     

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.     

Positioning of the arc discharge channel in vacuum arc facilities

The behavior of an electric arc in a magnetic field is studied theoretically and experimentally. It is found that the arc behavior can be governed by the ponderomotive interaction of the arc with current-carrying elements. In a nonuniform magnetic field, the behavior of the arc depends on the Hall currents and the diamagnetic properties of its plasma. It is shown that the position of the arc channel between the end faces of cylindrical electrodes can be controlled by nonuniform magnetic fields. The methods and devices considered in this paper allow one, in particular, to control arc heat sources used in the heat treatment of metals.     

双丝脉冲MIG焊接电弧光谱诊断及热源耦合机理分析

搭建了双丝脉冲MIG焊接试验系统,为了分析研究双丝脉冲MIG焊接的热源耦合机理以及电弧温度场,采用光谱技术对其电弧进行了诊断分析,采用中空探针法进行等离子体的辐射采集,得到电弧等离子体的光信号,利用Boltzmann图法计算了双丝脉冲MIG焊接电弧等离子体的电子温度,得出了电弧等离子体的电子温度分布规律,并结合电信号采集和高速摄像技术对电弧进行了综合分析。研究创新之处在于结合了电弧的高速摄像图片信息和电弧等离子体的光信号对双电弧耦合机理进行分析,对电弧温度场进行了较为直观的分析研究。试验结果表明,在本试验条件下焊接过程实现了推挽式输出,实现了一脉一滴的过渡方式;两个电弧在焊接过程中在磁场的作用下相互吸引,向中心发生了偏移,在双电弧的几何中心形成了新的热源中心,并且电弧发生上飘现象;双电弧电子温度整体呈倒V型分布,在双电弧几何中心位置,距工件表面3 mm的位置电弧电子温度最高,为16 887.66 K,比最低温度11 963.63 K高大约4 900 K。     

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 acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding

As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius.     

Variational method for solving radiative transfer problems

The variational principle is used to solve two problems of radiative transfer. The first one is the temperature distribution and radiative heat flux for a plane layer of ceramic material. While the second is the calculation of the integral blankness degree of a sphere filled with dust of an arc steel-melting furnace. Numerical results obtained shows good agreement with the published data.     

Application of vacuum arc cathode spot model to graphite cathode

A model of near-electrode processes is applied here to describe the behavior of cathode spots on graphite cathode in vacuum arc. The physical model is based on a kinetic treatment of cathode evaporation, electron emission from the cathode, and plasma production. The model consists of physical assumptions and a system of equations that are formulated in the paper. Spot parameters, such as cathode erosion rate, cathode potential drop, cathode surface temperature, current density, electric field, and plasma density, temperature, and velocity in the near-electrode region are calculated numerically. The calculation includes the dependence of spot parameters on spot current and spot lifetime. The variation of spot parameters as a function of spot lifetime are very strong at lifetimes shorter than 10 μs. The calculations indicate that Joule heating in the cathode body is significant, and may exceed cathode heating by the ion heat flux. Calculated spot parameters are compared with the corresponding experimental data for relatively low arc currents (<100 A) and their agreement is discussed     

材料热物性与热源强度辨识的改进遗传算法

建立二维非线性导热逆问题(IHCP)的数学模型.通过对基本遗传算法逐步改进得到三种不同改进阶段的遗传算法,分别用于反演导热问题中材料的导热系数及其内部热源强度,并比较遗传算法在各改进阶段用于求解导热逆问题时的收敛速度与求解精度,寻求一种使导热逆问题求解效率与计算精度更高的遗传算法改进策略.结果表明:提出的遗传算法改进策略达到了预期目的.