铝电解过程中R-C曲线的理论分析

通过对铝电解过程中氧化铝浓度与氧化铝分解电压、电解质本体电压、阳极气泡电压、阳极反应过电压以及阳极扩散过电压之间关系的理论计算分析,确定了铝电解槽电压与氧化铝浓度间的关联关系,并绘制出铝电解槽的R-C控制曲线,为实现铝电解过程中氧化铝浓度的控制提供理论依据。     

40 kA制钠电解槽流场的模拟研究

电解质在阳极气泡和阴极钠液浮力的作用下在制钠电解槽内循环流动,是典型的气—液—液三相流动。使用FLUENT软件建立40kA制钠电解槽三维流场的数学模型,通过计算得到了电解槽内气泡、钠液的浓度和速度分布情况,以及熔盐的流场分布图。     

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。     

铝电解槽阳极气泡行为研究

利用透明槽研究铝电解槽阳极气体行为.研究表明：阳极气体的生成是一个连续的过程,阳极侧部生成的气泡比阳极底部生成的气泡小.正对阴极的阳极表面生产的气泡比其它阳极部位上生成的气泡小,这是一个明显的现象.而且,正对阴极的阳极表面生成的气泡不会汇集成大气泡,这和其它阳极部位生成的气泡有很大的差异.阳极底部生成的气泡全部从阴阳极中间的电解质移动溢出电解质.阳极气泡的大小影响槽电压,气泡直径增大3 mm,槽电压增加0.21 V.同时,电流密度为0.5 A/cm2底部阳极气体离开阳极时槽电压的变化为0.16 V.电流密度为0.3 A/cm2,底部阳极气体离开阳极时槽电压的变化为0.12 V.     

铝电解过程中阳极气泡对槽电压波动的影响

铝电解过程中阳极底部产生气泡,气泡排放会引起电解槽的槽电压波动.本文采用透明槽进行铝电解实验,在阳极上施加恒定电流电解,电流密度为0.7 A/cm~2,观察气泡行为和气泡对槽电压影响,研究了水平阳极和阳极倾斜角为2°的条件下得到的气泡在阳极底部的形成长大过程,分析了气泡对槽电压的影响.结果表明:槽电压-时间曲线呈锯齿形状波动,每一个波动对应一个阳极气泡的形成周期.气泡刚逸出完时,槽电压最小,随着气泡的逐渐长大,槽电压逐渐增大,气泡将要逸出时达到最大.与水平阳极相比,阳极倾斜角为2°的条件下,气泡在阳极底面的停留时间变短了,电压-时间曲线也是呈锯齿形波动,气泡逸出的频率比水平阳极快,倾斜阳极气泡的周期平均为4 s,而水平阳极的气泡周期平均为9 s.     

铝电解阳极气泡图像Matlab处理研究

阳极气泡排放过程的运动会搅动电解质,对铝电解产生很大的影响,进行铝电解阳极气泡的研究可以掌握气泡的排放与电解质流动之间的关系。通过透明电解槽拍摄了铝电解阳极气泡的析出行为,用Matlab数学软件处理了实验过程所得到的图像。确定了灰度转化、直方图规定化、二值化、气泡特征提取的技术路线。采用该技术路线可以清晰地得到铝电解阳极气泡图像,提取气泡面积、质心等特征。研究发现,直方图规定化相比直方图均衡化可以获得更加清晰地气泡图像,二值化可以清晰的提取到气泡边部轮廓。通过以上技术路线,可以清晰的观察到原始图像无法分辨的气泡。用图像处理软件Image pro-plus 6.0获得气泡大小等特征,通过连续两帧气泡图像获得气泡速度,从而为进一步研究铝电解阳极气泡奠定了基础,还可以应用于冶金反应器的水模型实验等图像分析,稀土金属等其他金属电解过程的气泡行为研究等。     

NiFe_2O_4基惰性阳极的润湿性及气泡析出行为

利用座滴法和双室透明电解槽对NiFe2O4基惰性阳极的润湿性和气泡析出行为进行研究。结果表明,电解质对NiFe2O4基惰性阳极的润湿性要优于碳素阳极。在低电流密度情况下电解,阳极气泡的析出是一个动态过程,它先在阳极表面形核,以球形方式长大,小气泡在长大过程逐渐汇聚偏移,然后逸出。惰性阳极上析出的气泡尺寸比碳素阳极小,在阳极上的逗留时间也更短。大电流密度情况下,气泡的生成速度加快,尺寸降低,很难准确测量气泡的直径。     

阳极壁面向下倾斜对气泡影响的研究

以3kA钕电解槽为研究对象、相似理论为基础,建立了稀土电解过程的水模型物理试验平台,分别对几种不同阳极壁面倾斜角度工况下单气泡的生长过程进行试验,分析了电解过程中气泡脱离时间、气泡直径、滑移距离等参数的变化情况。结果表明,阳极壁面倾斜角度越大,气泡脱离时最大直径越大,脱离所需时间和滑移距离越大,越易造成阳极效应。     

不同开槽阳极铝电解槽的节能性研究

基于有限体积方法,建立三维传统阳极、纵向开槽和横向开槽阳极铝电解槽非稳态数学模型,采用磁动力流体模型(MHD)中电势法计算电磁场,把电磁力作为动量方程的源项,通过流体体积函数(VOF)法追踪电解质-铝液界面的波动,用离散相模型(DPM)追踪气泡的运动路径.对比分析传统阳极、纵向开槽和横向开槽阳极铝电解槽中电解质-铝液界面波动和气泡分布情况.结果表明,纵向开槽阳极下电解质-铝液界面波动幅度小于横向开槽阳极下的电解质-铝液界面波动幅度,且都小于传统阳极下电解质-铝液界面波动幅度.纵向开槽阳极底部的气体体积分数最小.     

稀土电解槽气液两相流动数值模拟

利用CFD软件,建立了稀土电解槽的阳极气泡及熔体整体流场数学模型。对稀土电解槽的阳极表面化学反应自动生成气体的流场进行了数值模拟,得出了电解槽的熔体整体流场分布图及在不同位置气体浓度分布曲线图,使之更贴近于电解槽的实际工况,为熔盐稀土电解槽的槽型优化提供依据。     

Investigation into the Total Dissolved Gas Dynamics of Wells Dam Using a Two-Phase Flow Model

Bubbles entrained by spilled water at hydroelectric projects increase the concentration of total dissolved gas (TDG), which may lead to gas bubble disease in fish. In this paper, the TDG dynamics downstream of Wells Dam are investigated using a two-phase flow model that accounts for the effect of the bubbles on the flow field. The TDG is calculated with a transport equation in which the source is the bubble/liquid mass transfer, a function of the gas volume fraction and bubble size. The model uses anisotropic turbulence modeling and includes attenuation of normal fluctuation at the free surface to capture the flow field and TDG mixing. The model is validated using velocity and TDG field data. Simulations under two plant operational configurations are performed to gain a better understanding of the effect of spill operations on the production, transport, and mixing of TDG. Model results indicate that concentrated spill releases create surface jets that result in the lowest TDG concentration downstream. On the other hand, spreading the spill release, with moderate flow through each gate, produces the highest TDG values downstream as a result of more air available for dissolution and smaller degasification at the free surface.     

Bubble Sizes, Breakup, and Coalescence in Deepwater Gas/Oil Plumes

Bubble size distribution (BSD) plays a major role in transport and fate of gas or oil released in deepwater. However, no reliable method is available to estimate gas or oil BSD after a deepwater spill. Breakup and coalescence have been identified as key processes controlling BSDs in turbulent jets. The present work introduces bubble breakup and coalescence processes for deepwater gas or oil spill models. A population balance equation representing bubble volumes is used to model the evolution of bubble sizes caused by breakup and coalescence. Existing theories for bubble breakup and coalescence rates in bubble columns are adopted to deepwater plumes. The advantage of the present model is that the BSD is generated as a result of breakup and coalescence; and therefore, a predefined BSD is no longer necessary for simulations. The comparison of model-computed results with laboratory and field data shows a good agreement. Scenario simulations show that the seed diameter given to start computations affects only for a short distance from the release point. Simulations also show that bubble breakup and coalescence is important only during the early stages of the plume where turbulence is dominant. The importance of accounting for gas bubble breakup and coalescence in estimation of gas dissolution is also demonstrated.     

气泡法测定多孔材料的中流量孔径

论述了用气泡法测定多孔材料中流量孔径的方法和数据处理过程。分析了中流量孔径计算方法和普通气泡法计算的平均孔径之间的差别。     

Theory of Initial Growth of a Microcavity in a Liquid Metal Around a Gas-Releasing Particle. Part 1. Physical and Mathematical Models

Certain inhomogeneities in a liquid can act as bubble nucleation centers. If such a center is a source of gas on a considerable scale, the bubble can grow rapidly to an appreciable size. The following model is proposed for analyzing this process: a solid sphere (compound containing a gas-forming element such as hydrogen) is surrounded by a liquid metal. The initial equations are as follows: the Navier-Stokes equation, in which there are terms containing the concentration of the gas component; the equation of continuity; and the equation for the convective diffusion of the gas component in the liquid metal. The growth of the bubble obeys an integrodifferential equation derived here, which reflects the effects of the hydrodynamic, diffusion, and capillary factors.     

<Emphasis Type="Italic">In Situ</Emphasis> Observation on Bubble Behavior of Solidifying Al-Ni Alloy Under the Interference of Intermetallic Compounds

The growth behavior of hydrogen bubbles and their interaction with intermetallic compounds during solidifying Al-Ni alloy were investigated by synchrotron radiation. The bubble growth can be divided as three stages, i.e., free growth, accelerated growth, and shrinkage. The free growth agrees well with stochastic model. The accelerated growth is attributed to the increase of hydrogen concentration and its gradient at the bubble–liquid interface caused by their contact. The negative hydrogen concentration gradient ahead of the bubble–liquid interface resulted in the bubble shrinkage. Also, the increasing gas pressure and decreasing Ni content promoted hydrogen dissolution.     

Modeling of Liquid Level and Bubble Behavior in Vacuum Chamber of RH Process

In the Ruhrstahl-Heraeus (RH)refining process,liquid steel flow pattern in a ladle is controlled by the fluid flow behavior in the vacuum chamber.Potassium chloride solution and NaOH solution saturated with CO 2 were respectively used as a tracer to investigate the liquid and gas flow behaviors in the vacuum chamber.Principal compo-nent and comparative analysis were made to show the factors controlling mixing and circulation flow rate.The liquid level and bubble behavior in the vacuum chamber greatly affect fluid flow in RH process.Experiments were per-formed to investigate the effects of liquid steel level,gas flow rate,bubble residence time,and gas injection mode on mixing,decarburization,and void fraction.The results indicate that the mixing process can be divided into three re-gions:the flow rate-affected zone,the concentration gradient-affected zone,and their combination.The liquid steel level in the vacuum chamber of 300 mm is a critical point in the decarburization transition.For liquid level lower than 300 mm,liquid steel circulation controls decarburization,while for liquid level higher than 300 mm,bubble behavior is the main controlling factor.During the RH process,it is recommended to use the concentrated bubble injection mode for low gas flow rates and the uniform bubble injection mode for high gas flow rates.     

Theory of Initial Growth of a Microcavity in a Liquid Metal Around a Gas-Releasing Particle. Part 1. Physical and Mathematical Models

Certain inhomogeneities in a liquid can act as bubble nucleation centers. If such a center is a source of gas on a considerable scale, the bubble can grow rapidly to an appreciable size. The following model is proposed for analyzing this process: a solid sphere (compound containing a gas-forming element such as hydrogen) is surrounded by a liquid metal. The initial equations are as follows: the Navier-Stokes equation, in which there are terms containing the concentration of the gas component; the equation of continuity; and the equation for the convective diffusion of the gas component in the liquid metal. The growth of the bubble obeys an integrodifferential equation derived here, which reflects the effects of the hydrodynamic, diffusion, and capillary factors.

     

Bubble Formation through Reaction at Liquid‐Liquid Interfaces

Slag foaming is an important phenomenon in steelmaking processes with both beneficial as well as negative effects. The present work is part of the wider project on the modelling of slag foaming, with special reference to dynamic conditions. Since bubble formation is the first step to foam formation, the present work was carried out in an attempt to simulate the bubble formation in slag/metal reactions in steelmaking processes by water‐modelling experiments. The bubble formation due to the gas produced through chemical reaction at the interface between oleic acid and sodium bicarbonate solution was systematically monitored. The chemical reaction rate was varied by varying the concentration of sodium bicarbonate. The bubbles were observed to be generated in the heavier aqueous phase just below the water‐oil interface. The bubbles penetrated the interface and escaped through the oil phase. The rate of the reaction was estimated from the volume of the gas that passed the water/oil interface. It was observed that the bubble formation and bubble growth mechanism were influenced by the reaction rate while the bubble size seemed to be unaffected by the reaction rate.     

Characteristics of round vertical gas bubble jets

Radial and axial profiles of gas concentration and bubble frequency have been measured for vertical gas bubble jets in the systems air/water, helium/water, and nitrogen/mercury using an electroresistivity probe. Gas velocities have been determined in the air/water system. All radial profiles were close to Gaussian. An integral model was applied to calculate axial distributions theoretically. Entrainment coefficients were determined for the experimental conditions. Axial profiles were correlated also in nondimensional representations. The bubble frequencies were used to compute local and average values of bubble size. Jet expansion and bubble size were found to depend considerably on the physical properties of the system. K. -H. Tacke and K. Schwerdtfeger were with Max-Planck-Institut für Eisenforschung when part of the experiment was carried out.     

Study on dimension and migration behavior of bubble under annular argon blowing at tundish upper nozzle

The water model experiments were carried out to study the bubble morphology in the tundish and mold with the process of annular argon blowing at tundish upper nozzle. The effects of the position of gas permeable brick, the casting speed and the argon flow rate on the bubble size distribution, the bubble migration behavior and the flow behavior of liquid steel near the liquid level in tundish were further investigated, coupled with the numerical simulation. The results show that with the process of annular argon blowing at tundish upper nozzle, a frustum cone shaped bubble plume can be formed around the stopper rod. The concentration of argon bubbles gradually decreases outward along the radial direction of the stopper rod. Owing to the wall attached effect, the bubble plumes float upward along the stopper rod, which can increase the collision probability between bubbles and the velocity of bubble plumes, causing a larger impact strength on the liquid level in tundish. In addition, a part of small bubbles are wrapped into the nozzle and the mold due to the drag force of liquid steel. With increasing argon flow rate, the number of bubbles in annular bubble plumes and the vertical velocity of liquid steel near the liquid level in tundish increase significantly. With increasing casting speed, the width and the bubble number of annular bubble plumes gradually decrease, leading to a decrease of the vertical velocity of liquid steel near the liquid level in tundish. Increasing the distance between the annular gas permeable brick and the center of tundish upper nozzle, the dispersion of bubbles and the width of bubble plumes increase, and the impact strength of bubbles acting on the liquid level in tundish becomes weaker. As the argon flow rate and the casting speed increase, and the distance between the gas permeable brick and the center of tundish upper nozzle decreases, the gas volume and bubble size in the mold increase. Under the experimental conditions, when the inner and outer diameters of the annular gas permeable brick are 110mm and 140mm, respectively, and the casting speed is 1.2m/min, the appropriate argon flow rate is 4L/min.