Fluid Dynamics of Vortex Formation in Tundish Operations: Mathematical Modelling

A mathematical model was developed to study the significance of the fluid dynamics of vortex formation in tundish operations. The aim is to contribute to the fundamental understanding of vortex formation and related phenomena. For this purpose a typical slab tundish was employed; the mathematical model was solved using FLUENT® commercial software capable to simulate highly turbulent flows. The well known k‐? turbulence model was applied to compute this effect in the process. The mathematical simulations confirmed the results from a water analogue model. The vortex formation is directly related to the highly turbulent flows present in the reactor. Great changes in velocity fields during short times and large distances between the upper edge of the dam and the free surface of the bath enhance the formation of vortex flows.     

双挡坝中间包内钢液的流动行为

通过采用水模拟和数值模拟分别对中间包不同结构进行全因素试验,研究了双挡坝结构对钢液流动行为的影响,着重探讨了不同类型的双挡坝中间包内钢液的流动状态和速度分布。结果表明:低坝应设置在高坝后,顶端钢液流速将减小29%,降低浇注末期发生卷渣的概率;低坝应与高坝流钢孔同高,钢液的平均停留时间可达到最大稳定值;高低坝距离差为40~160mm时,流体流动状态较稳定,低坝后无漩涡产生。分析认为:中间包入口区和出口附近均为强湍流状态,其他区域均为过渡流状态,入口区利于夹杂物的碰撞长大,应至少保证该区域长度大于中间包长度的1/4,出口区强湍流易产生大夹杂物导致水口堵塞,应控制在出水口附近0.25m的区域内。     

板坯连铸中间包挡坝结构优化的数学与物理模拟

通过几何相似比0.4的中间包水模型和Fluent数学模型对钢厂60 t二流板坯中间包不同结构挡坝下的钢液流动形态进行了分析。结果表明,中间包使用原结构-200 mm高无孔挡坝时钢液贴底流严重,且挡坝较低,对钢液提升作用不明显,不利于夹杂物上浮去除,浇注区形成较大死区。挡坝开向上15°两圆孔且高度增加至270 mm后,中间包内钢液滞止时间提高12.5%,死区减少36%,钢液在浇注区向钢液面流动,浇注区的死区和钢液温度分层现象基本消失。     

八流小方坯中间包结构优化

针对某钢厂八流小方坯中间包,采用数值模拟方法,对流场进行分析,结果表明,该钢厂使用的中间包结构不合理,近流有短路流出现,且各流差异较大,不利于去除钢液中的夹杂物,不利于提高各流间钢液的均匀性。通过改变挡墙孔高和坝高,分析了4种不同组合方案,并逐一进行流场分析,经过比较得出最佳中间包结构,消除了近流的短路流,即有利于夹杂物上浮和去除,同时也保证了各流间钢液的均匀性。     

鞍钢中薄板坯连铸中间包水模型实验研究

通过中薄板坯连铸中间包水模型实验,观察中间包水模型流场,优化设计中间包挡墙和坝的位置,分析了塞棒抑制钢水旋涡,减少卷吸的作用.     

两流非对称中间包流场准对称化的数学物理模拟

通过水模型实验和数值模拟,研究了不同湍流控制器下两流非对称中间包内流体流动特性。数值模拟结果表明：湍流控制器几何结构对两流非对称中间包流体流动特性有明显影响。圆形湍流控制器内流场涡心靠近底部,出口处流体流速垂直向上;中间包流场涡心靠近长水口,涡心高度与挡墙高度基本同高,中间包表面波动大,容易发生卷渣现象。不对称长方形湍流控制器底部为不对称波浪形,流场涡心靠近出口,流体以一定角度从湍流控制器出口流出;其右侧出口面积大于左侧,水口右侧流体流量大于左侧;由于增大了出口面积,出口处流体速度减小,中间包表面平稳。水模型结果表明采用不对称湍流控制器中间包两流之间的平均停留时间差比圆形湍流控制器中间包减少1/4,算术平均值增加5.3%,说明非对称湍流控制器增强了中间包去除夹杂物能力且能有效缩小两流之间流体流动的差异。     

连铸中间包内钢液流动特性及控流技术

中间包内钢液的流动状态对钢中夹杂物的去除效率影响较大。增加中间包容量可使铸坯内弧—侧Al2O3总量显著降低，在中间包使用挡墙和坝可减少内、外侧钢流温度差和拉漏发生率，去除钢中夹杂物。过滤器、湍流缓冲器和旋涡控制装置等相关技术的应用均提高了铸坯的清洁度。     

上水口环形吹氩对中间包内渣眼形成的影响

 中间包上水口环形吹氩可以在塞棒周围形成清洗钢液的环形气幕,同时部分氩气泡随钢液进入上水口内,可以减少非金属夹杂物在水口内壁的黏附,起到防止水口堵塞的作用。然而,不合理的吹氩量会导致中间包内液面渣层受过强的气液羽流冲击而形成渣眼,使得钢液裸露并发生二次氧化,严重影响铸坯质量。采用标准 k ε 湍流模型研究中间包内流体流动,采用DPM模型和VOF模型耦合方法,研究上水口环形吹氩条件下渣眼的形成及演化规律。结果表明,上水口环形吹氩在塞棒周围形成较强的上升流,塞棒上部邻近区域存在多个涡流区;在钢液涡流的影响下,中间包液渣下层远离塞棒区域,上层向塞棒区域迁移;随着吹氩量的增大,平均湍动能增大,塞棒附近钢液速度逐渐增大,钢渣界面钢液速度先增大后减小,渣眼边缘钢液速度先增大后减小然后再增大,速度与垂直方向夹角逐渐减小;增大吹氩量,中间包熔池液面形成以塞棒为中心的渣眼,渣眼面积逐渐增大。试验条件下不产生渣眼的临界吹氩量为4.2 L/min,对应的钢渣界面最大速度为0.247 m/s,与垂直方向夹角为70°。     

连铸钢包浇注过程中旋涡的形成机理

连铸钢包浇注末期出现的旋涡卷渣现象会对连铸钢水质量产生重要的影响,为了有效控制生产中的旋涡卷渣现象,对钢包浇注末期旋涡的产生机理开展详细研究.依据相似原理,构建了相似比为1∶6的钢包物理模型,对钢包浇注过程中旋涡产生及卷渣过程进行研究,分析了初始液面高度、出水口尺寸与布置位置、出水口结构等因素对旋涡形成规律的影响.结果表明：旋涡形成过程与初始液面高度无关;钢包出水口尺寸和布置位置对于旋涡形成过程影响显著.随着出水口直径的增大,旋涡临界高度逐渐增加;随着偏心率的增加,旋涡临界高度逐渐降低,最佳偏心率为3/4.提出三片挡块式出水口结构,可以显著降低钢包浇注末期的旋涡临界高度,降低高度达50％左右.     

不同挡墙挡坝组合对两流中间包内流场的影响

在相似理论的基础上,通过水力学模拟对两流板坯连铸中间包3种不同挡墙挡坝组合形式下包内流场进行研究.试验结果表明:方案1(挡墙-挡坝-端挡坝方案)挡墙与挡坝间距不合理,端挡坝未起到控流作用致使中间包内流体平均停留时间、峰值时间短,死区比例较大(27.9%);方案2(挡坝-挡墙-端挡坝方案)显著改善了中间包内流场状况,全混流区及活塞流区比例增加,死区减小为21%;方案3(双墙双坝方案)由于增加一组挡墙延长了流体流动的路径,流体在中间包内的停留时间明显增加,死区比例最小(16.7%),同时微观电导率波动值也最小(0.025 ms/cm),为3种方案之最优.     

二流T型23 t中间包控流装置的数值模拟和结构优化

通过计算流体力学软件FLUENT建立的数学模型对钢厂200 mm×1 600 mm铸坯二流T型23 t中间包现挡墙和坝、湍流控制器和坝、湍流控制器和现挡墙以及新挡墙4种结构方案进行三维数值模拟,研究原中间包及安装不同控流装置后的钢水流动特性。结果表明,在所有的设计方案中安装有湍流控制器和坝的中间包能够达到最佳优化效果;中间包的死区体积分率由30.18%降到16.51%,活塞流区与死区的体积分率比R_Vp/Vd由55.80%增大到129.44%;中间包内流动稳定,有利于夹杂物的上浮。     

中间包控制汇流旋涡的水模研究

 为了减小中间包汇流旋涡所造成的卷渣对钢质量的危害,就某钢厂现有中间包的各工艺参数对汇流旋涡形成的影响进行了水模实验研究,结果表明：小塞棒高度、小拉速和小中间包水口口径对防止汇流旋涡有利,渣在一定程度上可以抑制旋涡的产生和发展,但渣层的厚度对旋涡没有明显影响;塞棒高度为60 mm、拉速为068 m/min、中间包水口内径为56 mm和有渣是本实验所得的该钢厂实际中间包最佳防止汇流旋涡工艺条件。     

Numerical Investigation of the Fluid Flow in Continuous Casting Tundish Using Analysis of RTD Curves

 A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices (weir and dam) was carried out using the commercial CFD code FLUENT 60. The (k ε) two equation model was used to model turbulence. The residence time distribution (RTD) curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered (bare tundish, weir, weir+dam), the tundish equipped with the arrangement (weir+dam) is a best and optimal geometric configuration of tundish.     

抑旋板条件下多流中间包流动特性的数值模拟

以某厂35 t对称四流方坯中间包为研究对象,采用数值模拟方法研究了抑旋板对中间包流场特征的影响.结果表明:未加入抑旋板时,在端部的4流水口上方易形成逆时针旋涡,钢液面降至69 mm时便出现卷渣现象;在4流水口附近加入抑旋板,可以破坏水口处逆时针旋转流场,降低水口附近钢液流速,提高液面稳定性,对抑制汇流旋涡形成效果明显.改变抑旋板安放角度及高度,可使中间包内钢液均沿径向流入水口,钢液表面无明显旋涡形成,卷渣液位降低了40.6%,金属收得率显著提高.     

连铸中间包控流装置优化研究与实践

通过水力学模拟试验,研究了昆钢7号方坯铸机中间包采用多孔挡墙时的钢水流动特征.研究结果表明:中包采用多孔挡墙时,各流流动特征趋于一致,流体初次响应时间、平均停留时间增大,死区体积减小,中包冶金效果得到明显改善,3号多孔挡墙为最佳方案.试验结果应用于生产后,铸坯质量得到明显改善,TS800U铸坯非金属夹杂物出现率由52%降至3.5%.     

Hydrodynamic Modeling and Mathematical Simulation of Flow Field and Temperature Profile for Molten Stainless Steel in an Asymmetrical T‐Type Single‐Strand Continuous Casting Tundish with Arch or Round Hole(s) at Dam Bottom

In order to obtain the optimal structural parameters of the dug arch or round hole(s) at dam bottom in an 18–20 tons asymmetrical T‐type single‐strand continuous casting tundish, the flow field profiles and temperature profiles of molten stainless steel in the tundish with arch or round hole(s) at dam bottom have been investigated using hydrodynamic modeling coupled with mathematical simulation. The optimal structural parameters of arch hole(s) at dam bottom can be obtained from hydrodynamic modeling as that two arch holes with 30 mm as height and 50 mm as radius are symmetrically dug at dam bottom with the distance between arch hole center and dam center as 205 mm; or the optimal structural parameters of round hole(s) can be recommended as that one round hole with 70 mm as diameter is dug at left of the dam bottom with the distance between hole center and dam center as 205 mm. The results of mathematical simulation suggest that digging arch or round hole(s) at dam bottom with above‐mentioned structural parameters cannot obviously induce negative effects on streamlines and velocity vector profiles of molten stainless steel in the tundish by short circuit flow via arch or round hole(s) at dam bottom. The calculated temperature drop of molten stainless steel between the submerged ladle shroud and submerged entry nozzle in the tundish with arch or round hole(s) at dam bottom is about 3.0 K, the maximum temperature drop of molten stainless steel in the tundish is about 6.0 K.     

单流板坯中间包内湍流抑制器对流场的影响

通过水力学模型实验,研究了湍流抑制器对单流板坯中间包内钢液流动的影响,并比较了有无湍流抑制器时中间包内钢液流动的特性。湍流抑制器使钢液由长水口注入中间包后再返回,从而消除了中间包短路流,发展了表面流,延长了滞止时间和平均停留时间,有利于中间包内夹杂物的去除。湍流抑制器与单挡坝的结构在控制中间包内钢液流动方面效果较好。     

Investigation of Eccentric Open Eye Formation in a Slab Caster Tundish

Metallurgical and Materials Transactions B - Inert gas shrouding in tundish can result in the formation of a tundish open eye (TOE) due to the presence of reversed flows on the upper surface of the...     

Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model

Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm³/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm³/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.     

三流非对称中间包流场水模拟研究

在保证产量的情况下,为使夹杂物充分上浮去除,钢水温度均匀,进一步提高某钢厂320 mm×480 mm连铸方坯的生产质量,针对三流非对称中间包,设计1∶3水模拟试验和数值模拟,进行不同拉速和有无挡坝的研究。通过速度场和温度场的数值模拟以及不同拉速下的水模拟,可以发现,随着拉速的增加,三个水口的停留时间减小,并且三个水口的停留时间有一定差距。添加挡坝后随着拉速的增加,平均停留时间减小得更为缓慢。速度场和温度场的分布规律并不随拉速的变化而变化,但拉速的增加会使中间包内的速度和温度上升。