Modelling Study on the Plasma Flow and Heat Transfer in a Laminar Arc Plasma Torch Operating at Atmospheric and Reduced Pressure

A modelling study is performed to investigate the characteristics of both plasma flow and heat transfer of a laminar non-transferred arc argon plasma torch operated at atmospheric and reduced pressure. It is found that the calculated flow fields and temperature distributions are quite similar for both cases at a chamber pressure of 1.0 atm and 0.1 atm. A fully developed flow regime could be achieved in the arc constrictor-tube between the cathode and the anode of the plasma torch at 1.0 atm for all the flow rates covered in this study. However the flow field could not reach the fully developed regime at 0.1 atm with a higher flow rate. The arc-root is always attached to the torch anode surface near the upstream end of the anode, i.e. the abruptly expanded part of the torch channel, which is in consistence with experimental observation. The surrounding gas would be entrained from the torch exit into the torch interior due to a comparatively large inner diameter of the anode channel compared to that of the arc constrictor-tube.

Mathematical model on heat transfer of water-cooling steel-stick bottom electrode of DC electric arc furnace

For predicting and controlling the melted depth of bottomelectrode during the process of steelmaking, the water-cooling steel-stick electrode is taken as an example, to analyze the process ofheat transfer, then 3D mathematical model by control capacity methodis built. At the same time, the measurement on the melted depth ofbottom electrode is conducted which verified the correctness of thebuilt mathematical model. On the base of verification, all kinds ofkey parameters are calculated through the application and a series ofresults are simulated. Finally, the optimum parameters are found andthe service life of bottom electrode is prolonged.

Theory and Practice of Heat Transfer in Electric Arc and Flare Furnaces and Power Plants

The author describes the fundamental laws of physics, the laws of thermal radiation of ionized and non-ionized gas volumes. Based on open laws, a modern theory of heat transfer and methods for calculating heat transfer in electric arc and flare metallurgical furnaces, furnaces of steam boilers, and combustion chambers of gas turbine plants of power plants have been developed. The use of scientific discovery makes it possible to create innovative electric arc steel-smelting furnaces, flare heating furnaces, and combustion chambers in which the consumption of electricity and fuel is reduced, productivity and service life are increased, and the amount of harmful emissions into the environment is reduced.

Numerical Modeling of the High-Intensity Transferred Arc with a Water-Cooled Constrictor Tube

Stable and axi-symmetrical DC high-intensity transferred arcs with a coaxial water-cooled constrictor tube have been used to study the arc characteristics for many years. All the previous modeling studies concerning the high-intensity transferred arcs were restricted to the near-anode region. Modeling results are presented in this paper concerning the characteristics of the whole high-intensity transferred arc, referring to a recent experiment. It is shown that the computed flow and temperature fields for different flow rates of the working gas are overall similar, but a fully developed flow regime can only be achieved in the water-cooled constrictor tube at low working-gas flow rates. The predicted radial profiles of plasma temperature at the cross section near the constrictor-tube exit compare favorably with available experimental data, but corresponding comparison about the plasma axial-velocity profiles shows appreciable difference, revealing that there may exist considerable errors in the plasma velocity measurements using a sweeping Pitot tube.

Study on heat source model in twin-arc GMAW with a common weld pool

The heat input from arcs to weld pool in twin-arc gas metal arc welding （GMAW） with a common weld pool is investigated by high-speed photography. The characteristics of arc shapes and droplet transfer are studied and then the models for heat flux distribution on top surface of weld pool and enthalpy distribution of metal droplets transferred into weld pool are established. By using the model, 3-D geometries of weld pools in twin-arc GMAW with a common weld pool are predicted. Corresponding welding experiments on mild steel plates are carried out and the results indicate that the predicted shape of weld bead on cross section shows good agreement with measured one.

单向多孔材料在电弧中冷却性能的数值模拟

定向凝固制备的单向多孔材料在电弧加热器中可以替代水冷铜壁,提高电弧加热器的焓值和热效率,具有广阔的应用前景。针对单向多孔材料在电弧中的传热过程建立数学模型,利用数值模拟的方法研究了孔隙率、孔直径、通入角和注入率对单向多孔材料在电弧中冷却性能的影响规律。结果表明:孔隙率从7.9%增加到26.7%时,内壁面的热通量可降低约92%;在孔隙率和冷气流速不变的条件下,孔直径从0.3 mm增加到0.8 mm时,内壁面的平均温度从498 K增加到697 K;通入角的变化会同时影响单向多孔材料内壁面热通量和冷气注入率,进而影响材料的冷却性能;冷态气流注入率从14.2%增加到42.7%时,单向多孔材料内壁面热通量降低约17%。本研究结果可为单向多孔材料在电弧加热器中的应用提供参考。

基于高频变极性电流源的交叉耦合电弧焊摆动行为抑制

交叉耦合电弧焊工艺理论上可以实现焊接过程中传热、传质解耦和独立控制,具有很大的发展潜力,然而,传统的交叉耦合电弧工艺中旁路电弧电流一般由低频交流焊接热源提供,工作过程中会出现主电弧随着旁路电弧的极性改变而发生电弧摆动现象,使各个电弧之间的热力分配不平衡,传热、传质解耦不彻底.在增材制造应用中,会面临熔滴落点位置不可控、成型精度低等问题,为了解决主电弧的摆动问题,设计开发了旁路电弧为高频变极性电弧的交叉耦合电弧焊接热源.试验结果表明,这种焊接热源可以通过提高旁路电弧的变极性频率,有效地抑制主电弧的摆动行为,进一步实现交叉电弧中填充焊丝熔化速率与工件热输入之间的传热解耦,同时,抑制主电弧摆动后的现象表现为主电弧高频小幅度振动,理论上可以实现对熔池的搅拌作用,利于枝晶破碎、促进焊缝晶粒细化.

变位磁场强度对电弧熔积中电弧和熔池传热与流动的影响

目的研究变位磁场强度对变位磁场作用下电弧熔积中电弧和熔池传热与流动的影响规律与机理。方法基于流动动力学方程(麦克斯韦方程组、动量守恒方程、连续方程、能量守恒方程),建立了变位磁场作用下TIG电弧-熔池耦合的数值模型,对比分析了外加不同强度的变位磁场对电弧与熔池传热传质的影响规律与机理。结果外加变位磁场使电弧发生偏移,电弧等离子体具有偏向一侧与旋转的流动趋势,熔池的整体形貌向x正方向与y负方向发生偏移,熔池除了具有中心向外流动趋势以外,还具有偏向一侧与围绕中心旋转的趋势。随着变位磁场强度的增大,电弧与熔池整体形貌偏移量增大且偏向一侧与围绕中心旋转的趋势增强。结论外加变位磁场可使电弧发生偏移,且变位磁场强度增大,电弧与熔池整体形貌偏移量增大。

电弧增材制造传热传质数值模拟技术综述

电弧增材制造过程涉及丝材的送入和熔化,熔融金属向熔池的过渡,熔池中液态金属的对流、凝固和成形。缺陷的形成与电弧增材制造过程中发生的复杂多物理场现象密切相关。因此,需要借助高保真数值模拟技术来深入理解这些物理现象,并将其作为优化工艺条件、制造高质量产品的理论依据。本文综述了电弧增材制造传热传质数值模拟涉及的关键技术,并对未来研究方向进行了展望:首先,介绍了几种典型的热源模型,鉴于电弧增材制造过程中熔池的形成与演变是多种驱动力共同作用的结果,分析了浮力、电磁力、表面张力、电弧压力、电弧剪应力模型对流体流动和熔池表面变形的影响;然后,总结了三种金属过渡模型,包括速度入口填充液态金属、指定位置添加球状质量源项以及直接建立固态金属焊丝;最后,介绍了常用的气液界面跟踪方法。

CMT电弧增材制造铝合金传热传质与熔池行为数值模拟

为研究冷金属过渡(cold metal transition,CMT)电弧增材制造铝合金传热传质与熔池流动特性,基于Fluent软件建立了三维CMT电弧增材制造数值模型.模型中,采用动网格技术模拟焊丝竖直方向上的往复运动,利用流体体积法捕获气/液界面,焓-孔隙率法追踪固/液界面,并施加周期热量输入和阶段电弧力作用来等效电弧放电行为,研究分析了焊道成形传热传质过程与熔池动态行为.结果表明,焊道成形初期,熔池余高和坡度较大,形貌犹如半个球体,成形后期热量积累造成焊道余高后方较前方略小,而后端熔宽较前端略宽;单滴过渡周期内,焊丝机械回抽对熔池表面流动影响最为明显,液桥断裂产生较大反冲作用于熔池;熔池内部则是电磁力作为主导驱动力产生一股顺时针环流,环流随燃弧阶段周期切换而不断加强与减弱,并基本贯穿整个过渡周期,使得熔池内部热对流更加充分.模拟结果与试验结果显示吻合良好.

间接电弧焊技术的热量传输机制及研究现状

传统电弧焊技术焊接效率的提升伴随着焊接热输入的增加,不利于焊接质量的提升。间接电弧焊技术通过母材不接电极,实现了焊接效率与热输入解耦的效果,具有降低母材热输入的同时提高焊接效率的独特优势。本文对间接电弧焊与传统电弧焊的热量传输机制差异进行分析,并综述了现阶段间接电弧焊技术的研究现状。藉此指出,未来主要研究朝以下三个方向发展:一是研究多热源复合工艺;二是结合有限元建模技术研究熔滴行为特性及熔池热-力机制,促进空间多位置焊接适用性;三是研究异种焊丝的共同熔敷机理。

变位磁场作用电弧增材中电弧和熔池传热与流动数值模拟

为了揭示具有纵向和横向分量的外加变位磁场对TIG电弧增材成形过程中电弧和熔池传热与流动的影响机理,基于流体动力学软件Fluent,建立了电弧与熔池耦合的三维瞬态模型。对比分析了不同角度的变位磁场对电弧形貌、电磁力、热流密度、熔池形貌及熔池速度场的影响规律与机理。结果表明:无外加磁场时,电弧与熔池对称分布,施加变位磁场时,电弧和熔池中产生周向旋转和偏向一侧的电磁力,使电弧与熔池发生旋转与偏移,熔池除了具有由内向外的流动,还具有围绕中心旋转和偏向一侧的流动;增大变位磁场的变位角度使横向磁场分量减小,纵向磁场分量增加,从而使偏向一侧的电磁力减小,周向旋转电磁力增大,进而使电弧偏转与熔池偏移减弱,熔池旋转流动趋势增强。研究结论可为后续磁控电弧增材制造传热、传质的机理分析及工艺参数的选择提供理论依据和参考。

弧形涡流发生器对湍流相干结构及强化换热的影响

涡流发生器是一种常见的被动强化换热元件,因高性价比而受到广泛应用。本文针对带有弧形涡流发生器的方形管道,采用高时间分辨率粒子图像测速(Time-Resolved Particle Image Velocimetry,TRPIV)技术和大涡模拟(Large Eddy Simulation,LES)方法,研究了涡流发生器诱导的湍流相干结构特征及其对涡流发生器强化换热的影响。实验分析表明,湍流特征量统计图捕捉到了发卡涡涡腿和低速条带的印记。利用涡旋辨识准则提取了发卡涡和反向旋转的准流向涡对(Counter-rotating quasi-streamwise Vortices Pair,CVP),两者在弧形涡流发生器诱导的流场中共存且相互作用,随着涡旋结构演变与发展,其展向尺度不断增大。为研究湍流相干结构与强化换热的关系,通过数值模拟分析了湍流相干结构与温度梯度的空间分布情况,发现两者的分布具有良好的区域一致性,反映了湍流相干结构对强化换热的影响与控制。对比安装弧形涡流发生器前后的壁面平均努塞尔数,发现平均努塞尔数大幅提升,最大提升20%左右,且其沿流向的变化趋势与湍流相干结构的发展演化一致。

Fluid Flow Modeling of Arc Plasma and Bath Circulation in DC Electric Arc Furnace

A mathematical model describing the flow field, heat transfer and the electromagnetic phenomenon in a DC electric arc furnace has been developed. First the governing equations in the arc plasma region are solved and the calculated results of heat transfer, current density and shear stresses on the anode surface are used as boundary conditions in a model of molten bath. Then a two-dimensional time-dependent model is used to describe the flow field and electromagnetic phenomenon in the molten bath. Moreover, the effect of bottom electrode diameter on the circulation of molten bath is studied.

Non-equiliburum Modelling of the Electrical Characteristics of a Free-burning Arc

An arc model considering deviations from thermodynamic and chemical equilibrium has been developed in order to achieve a better understanding of the arc plasma close to material surfaces.The model is based on unified consideration of the thermionic tungsten cathode,the arc region and the flat anode made of copper.The heat transfer within the electrodes is coupled with the plasma through the energy fluxes onto the electrode boundaries.Electrical characteristics of an 8 mm long free-burning arc are presented along with findings from spectroscopic measurements of the plasma emission in atmospheric pressure argon.The arc current varied from 60 A up to 200 A,and the gas flow rate was set at 12 L/min(at atmospheric pressure,room temperature).

Analysis of the 3-D fluid velocity and temperature profile in keyhole plasma arc welding

Modeling and simulation of fluid flow and heat transfer in keyhole plasma arc welding is of great significance for optimizing the process parameters. In this study, a three-dimensional transient model is established to analyze numerically the heat transfer and fluid flow phenomena in keyhole plasma arc welding. VOF （volume of fluid） method is used to track the boundary of the keyhole. The dynamic developments of keyhole geometry, the fluid velocity field and temperature profiles are numerically simulated. And the changing Of the fluid velocity and pressure distribution on the keyhole wall in the forming process of the keyhole are analyzed.

Effect of Injection Position on In-Flight Melting Behavior of Granular Alkali-Free Glass Raw Material in 12-Phase AC Arc Plasma

An innovative in-flight glass melting technology with a multi-phase AC arc plasma was developed to save energy and reduce emissions for the glass industry. The effect of the injection position on the in-flight melting behavior of granulated powders was investigated. Results show that the injection position has a strong effect on the melting behavior of alkali-free glass raw material. With the increase in injection distance, the vitrification, decomposition, and particle shrinkage of initial powders are improved. Longer injection distance causes much energy to transfer to particles due to a longer residence time of powder in the high temperature zone. The high vitrification and decomposition degrees indicate that the new in-flight melting technology with 12-phase AC arc can substantially reduce the melting and refining time for glass production.

送丝速度对电弧增材熔池流动及焊道成形影响的数值模拟

通过数值模拟研究了不同送丝速度下电弧增材制造单道熔积成形过程中的传热传质及熔池流态,分析了送丝速度对焊道形貌的影响.结果表明,当送丝速度较小时,基板接受的电弧热较多,熔池的熔深较深且流动性较强,成形焊道较宽且高度较低;随着送丝速度的增大,熔融金属向上堆积,熔池体积增加,送丝速度达到一定值时,电磁力与表面张力达到动态平衡,熔深与焊道高度接近;当送丝速度较大时,液态金属对流减弱,熔深较浅,在表面张力的作用下,熔池边缘收缩导致焊道隆起.模拟与试验结果吻合较好,研究结果可以为GTAW电弧增材技术的工艺参数调控提供理论依据.创新点:通过数值模拟方法探究了送丝速度影响电弧增材制造熔池传热与流动,以及焊道成形的作用机理.

旁路等离子-MIG复合电弧及耦合熔池作用机理与数值分析

旁路等离子-MIG复合工艺是通过等离子焊枪的导电铜嘴与焊丝之间形成的分流弧、焊丝与母材之间的主路弧同轴耦合进行焊接的新型工艺,不但保持了MIG焊的高效性,还可以通过对旁路电流的调节实现焊接过程能量的精确控制.为了深入了解该工艺条件下复合电弧与耦合熔池的物理作用机制,通过建立流体动力学瞬态计算模型,并基于合理的试验验证,对旁路电流加载前后气液两相内部及界面处的传热传质行为进行了对比研究.结果表明,相比未加载旁路电流时,电弧的最高温度下降约1000 K,同时电弧与耦合熔池交界处的有效热通量整体下降;熔池内部液态金属回流速度明显下降,因此导致熔深和熔宽尺寸均有所减少;复合电弧和耦合熔池的最大电磁力方向没有改变,但数值均有所降低.

考虑空气对流换热的弓网电弧仿真研究

为了更精确地研究电弧的温度分布特性,提出一种考虑空气对流换热的弓网电弧放电模型。该模型基于磁流体动力学原理,添加对流换热项修正热平衡方程,通过COMSOL软件多物理场仿真得到了弓网电弧温度分布,并使用PG 2000型光谱仪通过Boltzman法验证了750 V下电弧中心5 mm处的温度,平台测量结果与模型计算结果基本一致,验证了模型的可靠性。研究结果表明:电弧柱区域内温度最高点出现在电弧柱中心距接触线表面1.42 mm处,并随着电压的提升高温区域不断向阴极扩散;空气流动速度的提升可以加快电弧的散热,避免其形成热集中区域碳滑板表面温度远高于接触线表面,其温度差为4160 K,表面温度随材料热导率的增大持续升高。