中间包钢液流动行为的数值模拟及控流装置优化

针对某钢厂四流大方坯连铸过程中铸坯夹杂物含量较高、各流流动状态不一致等问题,本文提出了关于中间包内控流装置(坝高和导流孔结构)的改进方案,采用数值模拟方法对比研究了不同方案下中间包钢液的流场及停留时间分布(RTD)等特征。结果表明,与原型中间包相比,适当增加坝高及下层导流孔的上倾角度,有利于改善中间包钢液的流动特性,各流之间的均匀性明显提高,钢液在中间包内的停留时间有所延长,死区体积分数下降,有效减弱了中间包短路流,中间包冶金功能得到改善;控流装置最佳参数为:坝高300 mm,上层和下层导流孔角度分别为20°和45°,此时对应的钢液在中间包内的平均停留时间为210 s,死区体积分数仅为13.2%。     

Fluid Flow in Tundish Due to Different Type Arrangement of Weir and Dam

Tundish is an important metallurgical reactor in the continuous casting process. In order to control the fluid flow in tundish and thus take full advantage of the residencetime available for the removal of inclusions from molten steel, the effect of weir and dam on the fluid flow has been studied in a water model based on the characteristic number Froude and Reynold number similarity criteria. The residence time distribution curves of the flow were measured by SG800. The optimum arrangement of darn and weir and the nonstationary flow in tundish were discussed. The results show that the combination of weir and dam is benefit for the flow pattern in tundish, weir can prevent the upper recirculating flow, dam can cut off the bottom flow and turn to upwards, it is advantageous to separate the nonmetallic inclusions. Furthermore, it is important to exceed the critical depth of bath during exchange ladles, not only for the inclusion floatation but also for avoiding tundish slag drainage earlier.     

基于RTD曲线连铸中间包优化设计数值模拟

为了优化连铸中间包内型,采用数值模拟方法计算钢液在连铸中间包内的停留时间分布(RTD),并通过RTD曲线分析了连铸中间包内挡坝高度和位置对其钢液流场的影响.结果表明,结构优化后的连铸中间包钢液流场趋于合理,死区体积分数由原始方案的17.62%降至13.29%,且钢液在连铸中间包内的停留时间变化不大.     

Improvement of tundish shape and optimization of flow control devices for sequence casting heavy steel ingots

The metallurgical effect of a round tundish used to cast heavy steel ingots in machine works at present was evaluated through water modeling experiments. The flow control devices of the improved oval tundish, which was used instead of the round tundish, had been optimized. The results show that the residence time of the round tundish is short, its inclusion removal efficiency is too low, and it has more dead zones and an unreasonable flow field. Compared with the round tundish, the improved oval tundish with the optimized weir and dam has a better effect:its minimum residence time is prolonged by 38.1 s, the average residence time is prolonged by 233.4 s, its dead volume fraction decreases from 26% to 15%, and the ratio of plug volume fraction to dead volume fraction increases from 0.54 to 1.27. The inclusion removal efficiency also increases by 17.5%.     

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

In a multistrand, the outlet near the inlet produces short circuiting flow. This leads to the formation of dead zones inside the tundish, and consequently, the mean residence time decreases. In the present study, numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model. To decrease the dead zone volume inside the tundish, the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied. The outlets near the inlet were closed for varying amount of time, and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish, namely, mean residence time and the ratio of mixed to dead volume of the tundish. An optimum closure time of the near outlet has been found, which yields best mixing inside the tundish. The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution (RTD) curves. The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish. The educational version of computational fluid dynamics (CFD) software PHOENICS was used to solve the governing equations and interpret the results in different forms.     

H型中间包与T型中间包的水模对比研究

进行了H型中间包的挡墙和坝的水模拟优化试验,确定出挡墙和坝的最佳设计方案。结合H型中间包的优点,与普遍使用的T型中间包进行了水模实验对比研究。研究表明：H型中间包内流动比T型中间包内更加稳定;当挡墙间距为130 mm、上挡墙高为87.5 mm、下挡墙高为52.5 mm时,H型中间包内液体的流动状态最好,死区体积比T型中间包小;符合工艺参数条件下增大中间包容积有利于停留时间的延长。     

蜗壳式旋风分离器内流场的特点

用五孔探针和热线风速仪测定了蜗壳式旋风分离器内的速度场和压力场,分析了上部入口结构、芯管插入深度和锥体长度对流场的影响.测定表明,蜗壳式旋风分离器内流场是一个非轴对称的三维湍流场.上部环形空间内有明显的顶部二次流存在,因而形成上灰环.芯管末端附近有较大的向心径向速度,呈短路流现象.在锥体下部有较大的偏心流,因而造成排尘口处粉尘返混,降低分离效率.斜底入口结构的旋风分离器可以减少二次流的流量,增加环心空间的径向速度,而对下部流场影响很小.芯管插入深度对芯管末端附近的径向分布有影响,而对短路流量影响很小.     

不同底坡有流流场中单个气泡运动的三维数值模拟

为了对不同水底地形和不同来流情况下,单个气泡上升并与自由表面相互作用的运动进行三维数值模拟,采用了VOF中的PLIC界面重构方法.结果表明:有无来流及来流大小对水平底面的气泡上升运动几乎没有影响.从不同水底坡度和不同来流速度耦舍下气泡运动发现,流速和底坡的耦合能有效增大气泡上升速度和自由表面抬升高度,并增大气泡变形.底坡坡度或速度越大,气泡相应物理量增幅也越大,变形更明显.     

单流板坯连铸中间包结构优化

通过对单流板坯连铸中间包的水模实验,研究了不同控流装置对中间包流动特性的影响.研究结果表明,堰、坝的尺寸和位置与湍流控制器(TI)的结构对中间包流动特性影响很大,在该中间包内使用不带顶檐的湍流控制器效果好于带顶檐的湍流控制器.与原方案中间包结构相比,优化后的中间包的流体流动特性得到很大改善,最小停留时间和峰值时间分别从64s和81 s提高到了81 s和163 s,平均停留时间从237s延长到了314 s,死区体积分数从35%降低到了14%,降低了60%.     

Optimization of flow control devices in a single-strand slab continuous casting tundish

The optimization of flow control devices in a single-slab continuous casting tundish was carried out by physical modeling, and the optimized scheme was presented. With the optimal tundish configuration, the minimum residence time of liquid steel was increased by 1.4 times, the peak concentration time was increased by 97%, and the dead volume fraction was decreased by 72%. A mathematical model for molten steel in the tundish was established by using the fluid dynamics package Fluent. The velocity field, concentration field, and the residence time distribution (RTD) curves of molten steel flow before and after optimization were obtained. Experimental results showed that the reasonable configuration with flow control devices can improve the fluid flow characteristics in the tundish. The results of industrial application show that the nonmetallic inclusion area ratio in casting slabs is decreased by 32% with the optimal tundish configuration.     

两流中间包流场的物理模拟与结构优化

研究了坝、堰的结构和安装位置对55 t两流板坯连铸中间包内流体流动状态的影响,结合RTD曲线计算出的平均停留时间,确定了优化的中间包结构。研究表明:坝、堰组合之后可以改变流体的流动状态,延长流体运动的轨迹,提高流体的平均停留时间,但流体经过坝、堰后都存在一定体积的死区。采用坝1、堰1组合方案的中间包结构最佳,该方案的平均停留时间最长为299 s,死区体积分数最小为31.0%。优化控流参数后,在坝、堰间距为290 mm,堰到长水口间距为383 mm时,流体在中间包内的平均停留时间最长为351 s,死区体积分数最小为19.0%,比不加坝、堰的方案平均停留时间增加了65 s,死区体积分数减小了15.0%。由Newton公式计算表明,此优化方案的中间包去除夹杂物的临界直径为17.5μm,在351 s内夹杂物均能上浮去除。     

40t 单流中间包控流装置的优化配置

采用水模型和工业验证的方法针对40 t 单流中间包的控流装置进行优化配置研究.通过对单独湍流抑制器控流装置、湍流抑制器+下挡墙组合控流装置、湍流抑制器+下挡墙+上挡墙组合控流装置的研究表明,下挡墙在改善钢液流动形态和减少中间包内死区方面所起的作用大于上挡墙.平均停留时间随下挡墙与长水口的距离增加呈先增大后减小的趋势.确定了单流中间包以湍流抑制器+下挡墙的优化组合形式,死区比例由原来的25.9%降低到了13.6% .通过系统取样分析发现优化后中间包内 T. O 和 N 含量大幅降低,正常坯中的大型夹杂物质量分数也由原来的8.4×10-7降低到3.2×10-7 .     

连铸中间包内夹杂物去除行为的物理模拟

通过选择乳状液滴模拟夹杂物和连铸中间包物理模型实验,考察了换钢包过程中,中间包初始液面高度、长水口注入流量及控流装置对中间包内夹杂物去除行为的影响规律.结果表明:中间包初始液面高度从工作液面的1/4到3/4过程中夹杂物去除率提高较快,3/4工作液面为较理想的换钢包操作液面;夹杂物的去除率随长水口注入流量的增加而增大,注入流量超过2.5m3h-1时,夹杂物去除效果明显改善;挡墙挡坝组合控流装置的去夹杂效果较无控流装置有明显改善,在此基础上加入抑湍器后,去夹杂效果明显改善.     

兴澄特钢中间包结构优化

以兴澄特钢连铸中间包为工程背景,根据相似原理建立了中间包水模型系统,研究了4流不同结构的中间包的流体流动特性.研究表明:原结构的中间包同一侧的两流之间的流体流动特性存在很大差异,与内侧流相比,外侧流的最小停留时间、峰值时间小,死区体积大,造成中间包内钢液温度不均匀,夹杂物不能有效地上浮去除,不能很好地满足高质量特钢生产的要求.采用优化后的挡墙和坝组合的中间包控流装置,外侧和内侧的停留时间分布趋于一致,表明外侧流和内侧流之间流动特性相近.中间包结构优化后平均死区百分数由原结构的58.2%降低到10.9%.     

侧壁式感应加热中间包磁/热/流耦合模拟

提出一种新的中间包感应加热方式,建立了三种线圈模型,模拟研究了三种线圈模型的电磁力分布及其对中间包内流场和温度场的影响,并结合RTD曲线评估了最佳线圈模型和加热功率.结果表明:感应线圈向端部移动有利于改善浇注区远端钢液流动形态及温度分布;相同加热功率条件下,U形感应加热线圈优于E形感应加热线圈,且相较于双侧对称分布U形线圈,单侧U形线圈的热效率更佳,冶金效果更好;提高感应加热功率有利于改善钢液的流动和提高铸坯的质量;对于四流中间包,加热功率为800~1 000 kW时,可达到均温补热的效果.     

离心式中间包流场的大涡模拟研究

为了研究离心式中间包的流动过程,采用大涡模拟(LES)方法针对3种不同情况,即(a)电磁力加直水口注流;(b)利用钢液的位能使用弯水口注流;(c)电磁力和弯水口注流共同作用,考察了影响旋流强度和中间包内流动结构的工艺参数.结果表明,LES方法可以成功模拟离心式中间包的三维湍流流场.与单纯电磁力或单纯弯水口相比,旋转电磁力和弯水口共同作用时可使水平面的旋流强度显著增强.在原有电磁力作用的基础上,使用弯水口注流可比原流场最大速度值增加约15%~19%.     

基于边界层风洞的下击暴流稳态风场特性数值模拟

针对下击暴流稳态风场模拟问题,基于计算流体动力学方法(Computational Fluid Dynamics,CFD),首先分别采用二维、三维冲击射流模型对下击暴流风场进行数值模拟,对下击暴流风场特性进行研究.在此基础上,根据下击暴流对桥梁结构作用主要受水平风速影响的特点,采用二维数值模拟方法对边界层风洞中设置倾斜平板模拟下击暴流水平风速风场进行了研究.最后,设计并加工了边界层风洞下击暴流水平风速模拟试验装置,在边界层风洞中进行了下击暴流水平风速风场模拟试验,并将数值模拟结果与试验结果和已有文献结果进行了比较.结果表明:下击暴流风场的二维冲击射流模型模拟结果与三维冲击射流模型模拟结果吻合较好,即二维冲击射流模型是一种有效的下击暴流风场简化模拟方法;在边界层风洞中设置倾斜平板所模拟的下击暴流水平风速风场数值模拟结果和风洞试验结果具有较好的一致性,并与冲击射流模型数值模拟结果和现场实测结果均吻合较好,即在边界层风洞中设置倾斜平板可模拟下击暴流水平风速稳态风场特性.     

卧管型多管旋风分离器的进气室内流场的研究

卧管型多管旋风分离器是一种新型高温、高效除尘设备.本文根据相似理论原理.设计了与卧管型多管旋风分离器进气室相似的实验模型.在入口总气量1580Nm~3/h下,用热线风速仪对模型中旋风管入口附近区域的流场进行了重点测试,总结出模型中旋风管入口附近的三维气流速度分布规律.并将其气流速度分布计算式无因次化.此流场分布规律可推广应用到与实验模型相似的装置上,为卧管型多管分离器进气室惯性分离模型的建立及其进气室的改进提出了必要的理论依据.     

1700板坯中间包温度场的数值模拟及其优化

以1700板坯中间包为研究对象,应用FLUENT软件计算了中间包的温度场。结果表明：原型中间包内钢液温度分布不合理,两个水口出口温度不一致,且温降较大。优化后中间包内钢液温度分布更加合理,尤其是坝体高度555mm,并设导流孔的方案3为最优方案,此时中间包内钢液最低温度为1820．6K,最大温差为5K左右,进出口温差为1．9K。     

1700板坯中间包温度场的数值模拟及其优化

以1700板坯中间包为研究对象,应用FLUENT软件计算了中间包的温度场.结果表明:原型中间包内钢液温度分布不合理,两个水口出口温度不一致,且温降较大.优化后中间包内钢液温度分布更加合理,尤其是坝体高度555 mm,并设导流孔的方案3为最优方案,此时中间包内钢液最低温度为1820.6 K,最大温差为5 K左右,进出口温差为1.9 K.