Behaviour of Argon Gas Bubbles in an Electromagnetic Driven Swirling Flow

An innovative steelmaking process is suggested using an electromagnetic driven swirling flow in the up‐leg of an RH vacuum degassing vessel. The effectiveness of this new process depends on the two‐phase flow behaviour of molten steel and argon gas. A physical and a mathematical model are developed to understand the effect of electromagnetic driven swirling flows on the behaviour of gas bubbles in the up‐leg of an RH vessel. Both water model experiments and numerical simulation show the distribution and trajectories of the gas bubbles. The gas bubbles’ trajectories are spiral and move towards the centre of the up‐leg in the swirling flow field. The accumulation of gas bubbles depends on the swirling number. At the same time, the swirling flow can prolong the residence time and trajectories of non‐metal inclusions in the vessel. The viscous drag force becomes important for small bubbles in the RH degassing vessel, and small bubbles have the trend to rotate with the swirling flow.     

大型铝电解槽电流效率数值建模研究

对铝电解槽内电流损失机理和现代大型槽(>400kA)的强湍流特征进行剖析,采用界面更新理论描述铝液—电解质界面附近的传质行为,建立了电流损失计算方程、质量传递系数方程及电流效率全域计算方程,进而结合多相流体力学及熔盐电化学相关理论,在CFX平台上建立了关联熔体运动的大型铝电解槽电流效率全域数值计算模型。应用该模型对某400kA级大型铝电解槽的电流效率进行了瞬态实时计算,求得全槽时均电流效率约为92.57%。     

Turbulent Flow and Transport of Bubbles in Slab Continuous Casting Mold Under Electromagnetic Brake

Large eddy simulation model with magnetohydrodynamics(MHD)is developed to study the effect of electromagnetic braker(EMBr)on molten steel flow and transport of argon bubbles in the continuous casting process.The large eddy simulation with Smagorinsky sub-grid scale model is used to calculate the turbulent variables.The results indicate that the magnetic force can optimize the molten steel flow pattern in the braking area.The flow is asymmetric,especially in the lower of the mold,even if with applied electromagnetic effect.The flow deviation of the molten steel in the mold is inevitable existence.More bubbles tend to release from the top surface with LMF-EMBr,while,FCMF-EMBr has little effect on the overall removal fraction of bubbles,but it affects the trajectory of bubbles.     

浅析加高阳极在铝电解槽上的应用对节能降耗的贡献

中铝某分公司针对的阳极交换周期低,经广大科技人员努力,将阳极碳块的高度由原来的550mm提高到570mm,该阳极碳块应用于电解槽上,使中铝某分公司的换极周期由28．5d调整为29．5d,阳极炭耗降至510kg／t·Al（含电解反应后残极剩余量）。同时,该阳极用于铝电解生产后,电解槽生产更加平稳运行,并减少了工人的劳动强度,提高了企业经济效益。     

Mathematical Modeling of Multi-sized Argon Gas Bubbles Motion and Its Impact on Melt Flow in Continuous Casting Mold of Steel

The 3D turbulence k-ε model flow of the steel melt(continuous phase)and the trajectories of individual gas bubbles(dispersed phase)in a continuous casting mold were simulated using an Eulerian-Lagrangian approach.In order to investigate the effect of bubble size distribution,the radii of bubbles are set with an initial value of 0.1-2.5mm which follows the normal distribution.The presented results indicate that,in the submerged entry nozzle(SEN),the distribution of void fraction is only near the wall.Due to the fact that the bubbles motion is only limited to the wall,the deoxidization products have no access to contacting the wall,which prevents clogging.In the mold,the bubbles with a radius of 0.25-2.5mm will move to the top surface.Larger bubbles issuing out of the ports will attack the meniscus and induce the fluid flows upwards in the top surface near the nozzle.It may induce mold powder entrapment into the mold.The bubbles with a radius of 0.1-0.25mm will move to the zone near the narrow surface and the wide surface.These small bubbles will probably be trapped by the solidification front.Most of the bubbles moving to the narrow surface will flow with the ascending flow,while others will flow with the descending flow.     

Computational Modeling of Microstructure Evolution in Solidification of Aluminum Alloys

In this article, a front tracking (FT) model and a modified cellular automaton (MCA) model are presented and their capabilities in modeling the microstructure evolution during solidification of aluminum alloys are demonstrated. The FT model is first validated by comparison with the predictions of the Lipton–Glicksman–Kurz (LGK) model. Calculations of the steady-state dendritic tip growth velocity and equilibrium liquid composition as a function of melt undercooling for an Al-4 wt pct Cu alloy exhibit good agreement between the FT simulations and the LGK predictions. The FT model is also used to simulate the secondary dendrite arm spacing as a function of local solidification time. The simulated results agree well with the experimental data. The MCA model is applied to simulate dendritic and nondendritic microstructure evolution in semisolid processing of an Al-Si alloy. The effect of fluid flow on dendritic growth is also examined. The solute profiles in equiaxed dendritic solidification of a ternary aluminum alloy are simulated as a function of cooling rate and compared with the prediction of the Scheil model. The MCA model is extended to the multiphase system for the simulation of eutectic solidification. A particular emphasis is made on the quantitative aspects of simulations. This article is based on a presentation made in the symposium ”Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties,” which occurred March 12–16, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.     

Physical Modeling of Fluid Flow in Ladles of Aluminum Equipped with Impeller and Gas Purging For Degassing

In the current study a transparent water physical model was developed to study fluid flow and turbulent structure of aluminum ladles for degassing treatment with a rotating impeller and gas injection. Flow patterns and turbulent structure in the ladle were measured with the particle image velocimetry technique. The effects of process parameters such as rotor speed, gas flow rate, and type of rotor on the flow patterns and on the vortex formation were analyzed using this model, which control degassing kinetics. In addition, a comparison between two points of gas injection was performed: (a) conventional gas injection through the shaft and (b) a “novel” gas injection technique through the bottom of the ladle. Results show that the most significant process variable on the stirring degree of the bath was the angular speed of the impeller, which promotes better stirred baths with smaller and better distributed bubbles. A gas flow rate increment is detrimental to stirring. Finally, although the injection point was the less-significant variable, it was found that the “novel” injection from the bottom of the ladle improves the stirring in the ladle, promotes a better distribution of bubbles, and shows to be a promising alternative for gas injection.     

Modeling of Three-Phase Flow and Interface Deformation of Metal/Bath in Aluminum Reduction Cell With Cathode Protrusion

Stabilizing the interface wave of the molten aluminum(metal)-electrolyte(bath)is beneficial to shorten the anode-cathode distance(ACD)which is critical to the energy saving.A coupled mathematical model was developed to study the impact of the novel cathode protrusion on the molten fluid motion as well as the metal-bath interface deformation.The molten fluid motion in the aluminum reduction ceils is under the combined effect of the electro-magnetic forces(EMFs)and the gas bubbles generated at the anode.A transient inhomogeneous three-phase model(metal-bath-gas bubble)was established in order to calculate more accurate.The results indicate that the metal-bath interface deformation can be reduced significantly by the novel cathode protrusion which is beneficial to the electric energy saving.Besides,The EMFs decreases as a result of the optimizing of the magnetic field due to the novel cathode convex which is an important driving force for the deformation of the interface.In addition,large vortex in the metal flow field is break up into the small vortex by the cathode protrusion and then dissipated due to the viscous force and the hindering effect of the cathode protrusion.The quantity of the vortex as well as the strength of the vortex reduces significantly in the reduction cell with novel cathode protrusion.     

开槽阳极对铝电解气液两相流及气泡分布特性影响的数值模拟

基于计算流体动力学原理,建立了全尺度三阳极铝电解槽内气液两相流三维CFD-PBM耦合计算模型,采用Grace曳力系数模型和Simonin湍流扩散力模型分别计算气液相间曳力和湍流扩散力,研究和讨论了开槽阳极对阳极底掌区域内气液两相流体流动及气泡分布特性的影响。结果表明,电解质流场预测结果与文献测试结果吻合良好;对阳极进行开槽可明显加快气泡的逸出方式,从而改变电解质流场和气体体积分数分布;长度方向开槽可明显降低气体体积分数和减小气泡索特平均直径。     

铝电解槽阴极内衬的发展

简速了我国铝电解工业在发展过程中。铝电解槽阴极内衬也在不断的发展及今后的发展方向。     

Carbothermic Reduction of Alumina by Natural Gas to Aluminum and Syngas: A Thermodynamic Study

The carbothermic reduction of alumina to aluminum by methane is analyzed by thermochemical equilibrium calculations in order to determine its thermodynamic constraints. Calculations predict that in the temperature range 2300–2500°C at 1 bar pressure, the reaction Al₂O₃ + 3CH₄ = 2Al +6H₂ + 3CO should occur without significant interference by the formation of unwanted byproducts such as Al₂O, Al₄C₃, and Al-oxycarbides, and with higher yields than by using solid carbonaceous compounds as reducing agent. The reaction was examined for several initial Al₂O₃/CH₄ molar ratios. The proposed process may be carried out in a fluidized bed reactor using concentrated solar energy, induction furnaces, or electric discharges as sources of high-temperature process heat. An important advantage of such a process would be the coproduction of syngas, with the molar ratio H₂/CO = 2, suitable for the synthesis of liquid hydrocarbon fuels and polymeric materials.     

瓦斯流动对电磁辐射频谱的影响

制造了大直径密封缸体,建立了瓦斯气体流动及电磁辐射测试的实验系统,用傅里叶变换对不同压力梯度和不同种类瓦斯气体在煤体中流动时电磁辐射的频谱进行了分析。结果表明,瓦斯气体流动产生的电磁辐射频带一般在较低频带,瓦斯流动时电磁辐射的主频带基本随压力梯度的升高而增大。压力梯度越大,瓦斯流动速度越高,对煤体的破坏作用越强,动电效应也越明显,裂隙振荡的频率也越高,从而产生的电磁辐射也越强,频率也越高。

     

Effect of Slotted Anode on Gas Bubble Behaviors in Aluminum Reduction Cell

Metallurgical and Materials Transactions B - In the aluminum reduction cells, gas bubbles are generated at the bottom of the anode which eventually reduces the effective current contact area and...     

异型阴极结构铝电解槽热应力场仿真

应用大型有限元软件ANSYS建立了160kA异型阴极结构铝电解槽和传统阴极结构铝电解槽的三维热应力模型,并对其进行了模拟计算。计算结果表明,异型阴极与传统阴极有着相似的位移分布,各方向上极值差别不大;异型阴极与传统阴极内部的应力场分布趋势基本相似,但异型阴极应力场要较为复杂。两种阴极正应力最大值差别不大,异型阴极XZ面的应力集中增高,XY面与YZ面的应力集中降低。阴极形状的改变使应力极值所在的位置由长轴两端变化为阴极凸起与阴极表面的连接处,因此需要在此处作加固处理。     

电流强化对铝电解槽电、磁、流场的影响

在一定的技术条件下通过电流强化可以提高电解槽铝产量和电流效率,降低单位产品的成本。本文以国内最具代表性的郑州龙祥铝业有限公司 154kA侧部四点进电铝电解槽为研究对象,具体分析了电流强化对铝电解槽电、磁、流场的影响。结果表明:当槽型结构与母线配置不变时,电流强化不影响铝电解槽铝液电、磁、流场总体分布规律,但改变铝液层电流密度、铝液磁感应强度和铝液流速大小;阴、阳极电流、铝液层电位差、铝液层电流密度均与系列电流强度具有相同的增加率;铝液层磁感应强度随系列电流强度的增加而线性增加;铝液最大流速、铝液平均流速均随系列电流强度的增加而增大。     

5kA级惰性阳极铝电解槽流场仿真研究

针对铝电解槽流场计算方法的不足,率先提出一种用于铝电解槽流场仿真计算的间接耦合方法,并使用此方法对5 kA级惰性阳极铝电解槽分别在电磁力、阳极气体、电磁力和阳极气体共同作用下的电解质和铝液流场分布情况进行了仿真计算。计算表明,计算方法能够合理计算出电解质和铝液在任一体积力作用下的流场分布。5 kA级惰性阳极铝电解槽电解质流动主要受阳极气体控制,铝液流动主要受电磁力控制。电解质在仅电磁力作用、仅阳极气体作用、电磁力和阳极气体共同作用下的平均流速分别为1.784 cm/s、3.657 cm/s、3.814 cm/s,铝液平均流速分别为1.295 cm/s、3.509 cm/s、3.696 cm/s。