钢液中球状夹杂物颗粒受力情况的数值模拟

通过理论分析和数值模拟的方法,研究了1873 K钢液中球状夹杂物颗粒运动过程中的受力情况.静止钢液和湍流场中,夹杂物颗粒所受的压力梯度力、虚拟质量力、Saffman力及Magnus力较小,可以忽略不计.静止钢液和均匀湍流场中,随着夹杂物颗粒尺寸的变大,颗粒所受Brown力逐渐衰减,当夹杂物颗粒直径大于20μm时颗粒所受Brown力基本不会对其运动造成影响,可以忽略不计.小于10μm的夹杂物颗粒布朗运动较为剧烈,单位质量夹杂物颗粒所受Basset力和Brown力较大,成为主导夹杂物颗粒运动的主要作用力;尺寸较大的夹杂物颗粒(直径D>50μm),Basset力、质量力和Stokes力共同作用影响夹杂物颗粒的运动、碰撞和去除.      

纳米Fe_2O_3粉末的表面吸附性能

采用TG-DTA结合XRD等实验方法,研究纳米级Fe2O3粉末的表面吸附性能;分析Fe2O3粉末表面吸附水量及脱附热与纳米颗粒尺寸的依赖关系;利用数学模型结合热力学理论定量描述纳米Fe2O3颗粒的比表面能和表面过剩吉布斯函数,及其随颗粒尺寸的变化关系。结果表明:随纳米Fe2O3颗粒尺寸减小,脱附水的温度区间逐渐增宽,脱水量和脱附热增大;且比表面积的显著增大导致比表面能、表面过剩吉布斯自由能明显升高,纳米颗粒吸附性能增强。     

连铸板坯内部缺陷及结晶器内钢液电磁流动的控制

利用水模实验和流场数值模拟相结合的方法对连铸过程凝固壳俘获气泡和夹杂物的行为以及结晶器内钢液的湍流和气泡对夹杂物的吸附进行了研究。水模实验揭示了湍流的存在,说明液流在水口不同喷口处的流速不同。通过流场数值模拟估计了钢液流动的湍流流速。利用X射线扫描法,研究了与拉坯方向垂直的铸坯模截面的气泡分布。通过扫描电镜（SEM）观察黏附在气泡表面的Al2O3颗粒数量。为防止气泡进入钢液内部,采用流动控制结晶器（FC）和电磁水平稳定器（EMLS）2种类型的电磁流动控制系统来减少射流速度对结晶器窄边的冲击。     

金属液的脱氮

本文综述了金属液熔渣脱氮、真空脱氮和气泡携带法脱氮方法。熔渣脱氮热力学研究主要涉及脱氮反应和熔渣的氮容量。真空度、氩气搅拌和金属液中氧、硫浓度是影响真空脱氮和气泡携地脱氮的主要因素。     

轴承滚动体研磨钢泥废料表面油污去除

轴承滚动体研磨过程中使用一些磨液以起到润滑和冷却作用。磨液为水、油酸以及配加的少量氢氧化钠,因此,钢泥废料表面会吸附上含有油酸和油酸钠的研磨油污,该油污对钢泥废料的后续还原处理生产还原钢粉产生不利影响,必须予以去除。采取400℃蒸馏挥发脱附法对轴承滚动体研磨钢泥废料表面油污的去除进行了研究。通过热重的方式研究了钢泥表面油污挥发脱附的失重情况,得出400℃钢泥表面油污挥发脱附大约需要17.1min,油污的挥发脱附满足二级动力学模型;通过油污蒸馏挥发脱附机理研究,明确油污脱附既要满足热力学条件,同时也受油污蒸汽溢出动力学影响;400℃氩气气氛下油污挥发后碳质量分数由2.89%降至0.76%,钢泥表面油污去除效果较好。     

机械搅拌反应器内气体分布的数值模拟

机械搅拌反应器内通常包含气、液、固等多相体系,利用计算流体力学方法针对其内部复杂物料运动的模拟近年来取得了很大进展。欧拉双流体模型被用来模拟一种装配Rushton型叶轮机械搅拌反应器内包含气泡的气液两相流,并通过不同的相间力模型及自定义湍流子模型描述槽内气泡复杂运动。分析了不同曳力、气泡诱导湍流、升力、湍流分散力等模型在模拟气泡分布时的效果,并将模拟结果与Barigou和Greaves的试验结果进行比较。结果表明,提出的模拟方法在机械搅拌反应器模拟中能够得到准确的气体分布结果。     

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。     

强搅拌调浆在金川硫化铜镍矿浮选中的作用机制研究

通过浮选试验、粒度分析测试和扫描电镜(SEM)分析,研究强搅拌调浆在金川硫化铜镍矿浮选中的作用,并考察其作用机制。浮选试验结果表明:强搅拌调浆能够提高金川硫化铜镍矿的浮选指标,强搅拌的时间越长,强度越强,金川硫化铜镍矿的浮选指标越好。固定调浆时间为20 min,当调浆强度从1950增加到2800 r·min-1时,镍的浮选回收率从81%增加到87%。金川硫化铜镍矿中的蛇纹石矿泥与硫化矿物颗粒表面电性相反,容易通过静电吸引作用吸附在硫化矿物表面形成矿泥罩盖层,细颗粒矿泥的罩盖阻碍了硫化矿物颗粒和气泡的粘附,降低了硫化矿物的浮选回收率。粒度测试和扫描电镜分析结果证实了金川硫化铜镍矿中的粗颗粒硫化矿物表面罩盖有细颗粒矿泥,矿泥的主要成分为蛇纹石等含镁硅酸盐矿物。对矿浆进行强搅拌调浆能够脱附硫化矿物表面罩盖的蛇纹石矿泥,蛇纹石矿泥粒度越粗,越容易从硫化矿物表面脱附,而粒度极细的蛇纹石矿泥较难脱附。强搅拌的强度越强,时间越长,硫化矿物表面罩盖的蛇纹石矿泥数目越少,越容易与浮选气泡粘附,浮选回收率越高。     

转炉冶炼脱磷过程数学模型

在对复吹转炉脱磷过程的机理分析的基础上,应用冶金热力学、动力学、传输原理和反应工程学理论,建立了转炉冶炼脱磷过程数学模型,确定了模型的有关参数.模型的     

粒度大小对赤铁矿和石英浮选分离的影响

通过浮选试验、DLVO理论计算、聚焦光束反射测量（FBRM）等研究了油酸钠浮选体系下粒度大小对赤铁矿和石英浮选分离的影响。人工混合矿浮选试验表明,窄粒级粗粒或中等粒级的赤铁矿?石英混合矿（CH&CQ和MH&CQ）的浮选效果较好,其中CH&CQ和MH&CQ的分选效率分别为85.49%和84.26%,明显高于全粒级混合矿（RH&RQ）的分选效率74.94%;但窄粒级的细粒赤铁矿?石英混合矿（FH&FQ）的浮选效果则较差,其分选效率只有54.98%。浮选动力学试验表明,赤铁矿的浮选速率和回收率不仅与赤铁矿的粒度有关,还受石英粒度的影响,细粒脉石矿物石英会降低赤铁矿的浮选速率和回收率。DLVO理论计算表明,当矿浆pH值为9.0时,石英与赤铁矿颗粒间的相互作用力为斥力,此时细粒石英很难“罩盖”在赤铁矿表面并通过这种“直接作用”的方式抑制赤铁矿浮选,这也与聚焦光束反射测量（FBRM）的测定结果基本一致;颗粒?气泡碰撞分析表明,在浮选过程中细粒石英可能通过“边界层效应”的方式跟随气泡升浮（夹带作用）,影响赤铁矿颗粒与气泡间的碰撞及黏附,从而降低了赤铁矿的浮选速率和回收率。      

Flotation Kinetics

Abstract

The physical variables that influence the rate of flotation are examined. The probabilistic model of flotation is used to establish the effect of the particle si2e and density, bubble size and agitation on the rate of flotation

In quiescent flotation, it appears that the flotation rate is limited by the particle-bubble collision and subsequent attachment of the particle to the bubble. For fine (<20 μm) or low density particles the remedy for low recovery rates would be to either use small bubbles of the order of 100 μm, or to use moderate to high agitation with larger bubbles

In the usual turbulent conditions, the limit is set by the destruction of the bubble-particle aggregates. Broadly speaking, the same parameters favour both attachment and detachment so that the ultimate flotation rate is a compromise between these two competing mechanisms

The bounds which define the best agitation level and bubble size to use are strong functions of the particle size and density. This results in conflicting requirements for the optimum flotation of the fine and the coarse particles. Best conditions for the flotation of each are indicated.     

Interaction of reactive oily bubble in flotation of bastnaesite

To understand the flotation mechanism of bastnaesite using reactive oily bubble, the interaction between bastnaesite parti-cles and reactive oily bubbles was investigated by electro-kinetic studies, induction time measurements and small-scale flotation ex-periments. The bastnaesite flotation could be seen as a hetero-coagulation between bastnaesite particles and reactive oily bubbles which was confirmed by the zeta potential distribution and induction time measurements from pH 4.8 to pH 9.0. The small-scale flotation tests were consistent with the hetero-coagulation results, and showed a better flotation of reactive oily bubble than air bubble among all pH range. The interaction force between bastnaesite particles and reactive oily bubbles was evaluated by the classical DLVO theory. It indicated that the attachment could be predicted well by the DLVO theory only in a restricted pH range due to the absence of hydrophilic interaction repulsion force and chemical interaction force.     

Aggregation Kinetics of Inclusions in Swirling Flow Tundish for Continuous Casting

 The mechanism of inclusion aggregation in liquid steel in swirling flow tundish is analyzed by applying the theory of flocculation which was developed in the field of colloid engineering. The gas bridge forces due to the micro bubbles on hydrophobic inclusion surfaces were considered responsible for the inclusion collision and agglomeration, which can avoid the aggregation to breakup. The quantity of micro bubbles on hydrophobic inclusion particle is more than that on hydrophilic one. The trend of forming gas bridges between micro bubbles on particles is strong in the course of collision. The liquid film on hydrophobic particles is easy to break during collision process. Hydrophobic particles are liable to aggregate in collision. According to the analysis of forces on a non-metallic inclusion particle in swirling chamber, the chance of inclusion collision and aggregation can be improved by the centripetal force. Hydrophobic particles in water are liable to aggregate in collision. Hydrophilic particles in water are dispersed although collision happens. The wettabiliy can be changed by changing solid-liquid interface tension. The non-metallic inclusion removal in swirling flow tundish is studied. It shows that, under certain turbulent conditions, the particle concentration and the wettability between particles and liquid steel are the main factors to induce collision and aggregation.     

Development of investigation techniques of froth flotation from the beginning of its wide industrial use. Part two. Methods of evaluation of the adsorption and orientation of heteropolar molecules of reagents in the adsorption layer on the surface of particles

Methods for evaluation of the adsorption and orientation of heteropolar molecules of reagents in the adsorption layer on the surface of particles and the adsorption of reagents on the surface of bubbles are considered. Experiments of nonfrothing flotation from a turbulent medium, methods of froth flotation (FF) with a limited air consumption, measurement of detachment forces simulating the FF, determination of the adherence times of the particles to the bubbles, and measurement of the contact angles can be used to reveal the character of the orientation of adsorbed molecules or ions of reagents. To evaluate the adsorption of reagents on the surface of bubbles, only static procedures for determination of the surface tension (σ), methods of recording the relaxation curves σ(t), and methods for evaluation of froth formation and destruction can be used. This possibility is reviewed to establish the relation between the definite properties of reagents and their concrete effect under the dynamic FF.     

Fundamental of Inclusion Removal from Molten Steel by Rising Bubble

The mechanism of inclusion removal by attachment to rising bubble was analyzed, and the movement behavior of inclusion, the mechanism of bubbles/inclusion interaction, collision probability and adhesion probability were discussed. A mathematical model of inclusion removal from molten steel by attachment to fine bubble was developed. The results of theoretical analysis and mathematical model showed that the optimum bubble diameter for inclusion removal is 1 to 2mm. A new method that argon is injected into the shroud from ladle to tundish during continuous casting has been proposed to produce fine bubble. It provides theoretical guides for production of super clean steel.     

Mathematical modeling and computer simulation of the rotating impeller particle flotation process: Part I. Fluid flow

Removal of unwanted particles from molten metal by flotation is one of the most useful melt cleansing techniques used by the foundry industry. An effective way of flotation of particles in a melt relies on purging a gas into the molten metal through holes in a rotating impeller. Impeller rotation creates turbulence inside the melt, which helps agglomerate the impurity particles and, thereby, enhances their removal from the melt. In addition, turbulence increases the probability of particles attaching to the rising gas bubbles and, therefore, enhances the chance of their removal from the molten metal. A mathematical model has been developed to simulate the turbulent multiphase flow field inside the flotation treatment furnace. Simulations based on the model were used to demonstrate the effect of the various process parameters on the performance of a batch-type rotating impeller particle flotation process.     

Investigation of froth flotation and selection of reagents on the basis of the mechanism of their effect: Report 1. Substantiation of the selected methods for investigation of the process

Three strengthening components of the particle-bubble contact that emerges under the effect of appearance of the external detachment force f in the dynamic conditions of froth flotation are considered. These are the flexure of the bubble surface at the contact perimeter, the increase in the contact angle θ, and the local increase in the surface tension σ on the bubble surface near the perimeter of its contact with the detached particle. Using the equations of capillary physics and experiments, three possible mechanisms of flexure of the bubble surface (which are caused by the effect of gravitation and reagents, namely, classical, hysteresis, and capillary mechanisms) are revealed. The necessary properties of reagents, which promote such flexure under the effect of f, are established. These are their ability to selective hydrophobization of the particle surface and to the local increase in the surface tension σ on the stretched bubble surface. Two groups of simple methods are recommended to investigate the process and to select reagents which model the process of froth flotation: (i) to evaluate the ability of reagents to vary the wettability of the particle surface—flotation experiments in frothing and nonfrothing apparatuses and to measure detachment forces, the time of adherence of the bubbles to the particles, and contact angles; (ii) methods for recording the relaxation curves and evaluating frothing properties (for reagents acting preferentially on the bubble surface). The effect of the capillary pressure of the gas in variously sized bubbles on the value of detachment forces of the particles from them, as well as the invariance of these forces of σ during slow detachment, are shown.     

Mathematical Model for Growth and Removal of Inclusions in Molten Steel under Gas‐stirring Conditions

A three‐dimensional mathematical model has been developed to predict growth and removal of inclusions during gas stirring through eccentric tuyeres in a ladle. In the model, the efficiency of inclusion removal is investigated under three different collision mechanisms: Brownian, turbulent and Stokes collision. The Importance of the three approaches of wall adhesion, Stokes flotation and bubble adhesion on inclusion removal is analysed and the efficiency of inclusion removal through three types of tuyeres in central, eccentric and multi‐tuyere form is studied. The results indicate that inclusion growth resulting from turbulent collision is most important and the effect of Stokes collision is remarkable with increased inclusion size, while inclusion growth resulting from Brownian collision is negligible. Removal by Stokes flotation is the main mechanism for large inclusions, while inclusion removal by wall adhesion is negligible. The smaller the bubbles are, the higher the efficiency of inclusion removal is. The type of tuyere arrangement has a great effect on inclusion removal. Inclusion removal in a 135t ladle with one eccentric tuyere is more efficient than in a ladle with central tuyere or multi‐tuyere design.     

Interactions between a Small Bubble and a Greater Solid Particle during the Flotation Process

ABSTRACT

The interaction between bubbles and solid particles is an important mechanism in many industrial processes and flotation is a significant component of the most utilized applications. While flotation of mineral ores deals with fine particles and larger bubbles, the aim of this review is to focus on the opposite case; the interaction between smaller bubbles and larger particles encountered mostly in plastic flotation. Plastic flotation seems to be one of the appropriate methods for separating plastics, which is necessitated by increasing plastic consumption and the growing need to recycle. The first part of the article focuses on the problem of the collision of a bubble with a particle, both spherical and planar. The collision efficiency is discussed. The second part is devoted to the problem of liquid film rupture and the creation of the three-phase contact line. The third and final part focuses on the problem of the three-phase line expansion and the effect of surfactants on the resulting bubble stability.     

Solidification processing of Al-Al2O3 composite using turbine stirrer

Solidification processing of Al-Al₂O₃ composites involves mixing of nonwetting alumina particles in molten aluminum alloy resulting in a slurry where the particles are often attached to bubbles sucked at the center of vortex below the stirrer. The internal surface of bubbles is eventually oxidized by oxygen from air entrapped in it. These bubble-particle combines may float or settle during casting depending on the overall density influencing the particle and porosity distribution in a cast composite ingot where the performance of a stirrer may be evaluated under a given condition of processing. Particle incorporation is more for turbine stirrers instead of flat blade stirrers, but the porosity also increases. Flotation of bubble-particle combines during casting of ingot results in higher particle content at the top. Microstructure shows clusters of particles along circular boundaries of thin oxides at the top of the ingot and sometimes at the bottom. This may be a consequence of filling of bubbles to different extents by surrounding liquid puncturing the oxide layer, if necessary, during solidification. When the manner of stirring is changed to 2 minutes of stirring of particles into molten alloy with an intermediate 2-minute period of no stirring before stirring the slurry again for 2 minutes, relatively uniform particle incorporation results along the height of cast ingot compared to that obtained by continuous stirring. This difference in particle distribution may be attributed to flotation of bubble-particle combines to release the particles on the top of the slurry when stirring ceases and its remixing into the slurry when it is stirred again. However, an increase in the intermediate period of no stirring and a higher processing temperature result in enhanced porosity and a more inhomogeneous particle distribution along the height of the ingot.