Water model simulation of tundish flow under varying conditions

Water model studies have been conducted to characterise the flow conditions in continuous casting tundishes under conditions of open and submerged nozzles. In this investigation simulations of practical problems of flow interruptions from the ladle, thermal inversions due to uninsulated ladle, and pneumatic agitation near the tundish end wall were conducted. The studies showed that incorporation of suitable flow control devices brings about homogenisation of temperature and composition between strands in the above cases. This study also showed that agitation of the liquid at the end wall reduces the extent of stagnant zone in the tundish.     

Fluid flow behaviour in slab continuous casting tundish with different configurations of gas bubbling curtain

Abstract

Fluid flow characteristics in a two strand slab continuous casting tundish with different configurations of argon gas bubbling curtain (GBC) were investigated in physical modelling experiments. It was found from this research that the GBC with a small flow rate acted as a gas dam and could greatly improve the flow characteristics in the tundish. It increased dramatically the peak concentration time and plug flow volume, decreased greatly the dead volume, created surface directed flow and eliminated short circuiting. Therefore, the fluid flow characteristics in a tundish with GBC were favourable to the floatation and separation of inclusions from molten steel. The flow characteristics with low gas flow rate and short distance of the bubbling curtain from the tundish outlet were better than those with high gas flow rate and large distance of the curtain to the outlet. The optimal configuration for the improvement in fluid flow characteristics was turbulence inhibitor (TI)–weir–dam–GBC (TI–W–D–GBC), followed by TI–channel weir (CW)–GBC, TI–W–GBC and TI–GBC.     

吹氩连铸中间包内钢液流动特性的水模型实验研究

建立了模拟连铸中间包底吹氩流动过程的水模型.通过测定分析水模型的RTD（停留时间分布）曲线研究了吹气流量、吹气位置及控流元件对中间包内流动特性的影响规律,并对此进行优化.结果表明：条形透气梁安放位置对中间包内的流动特性影响最为显著,均匀开孔的多孔挡墙和条形透气梁喷吹氩气二者的配合使用能获得理想的流动特性.     

中间包气幕挡墙水模与工业试验研究

通过水模型实验和工业试验,研究了中间包底吹氩气对中间包流场和去除铸坯大型夹杂物行为的影响。水模型实验结果表明:中间包底吹气可以改善中间包流场,减少死区体积比,增加平均停留时间。不同实验参数对中间包流体流动特征值的改变程度不同。工业试验结果表明:中间包采用气幕挡墙后,中间包长水口处到铸坯的全氧质量分数降幅提高60.62%;每10kg试样夹杂物总含量由3.85mg降至2.88mg,去除大型夹杂物效果明显,尤其是尺寸小于140μm的夹杂物。     

Transient steel quality under non-isothermal conditions in a multi-strand billet caster tundish: part I. Analysis of fluid flow,thermal behaviour and inclusion behaviour

A numerical model based on computational fluid dynamics was used to simulate the effect of non-isothermal conditions on melt flows in a multi-strand billet caster tundish. To start with, water was used as the operating fluid in a one-third scale tundish to calculate the fluid flow and temperature fields under isothermal and non-isothermal conditions. The model was then extended to the full-scale tundish with molten steel as the operating liquid in order to simulate the conditions in a real plant. It was observed that using step inputs of 10° and 23° for water and steel cases, respectively, changed the fluid flow patterns significantly, more so at locations far from the inlet, due to stronger buoyancy-driven natural convective flows. The temperature distribution and inclusion trajectories within the tundish were also affected due to the presence of non-isothermal conditions.     

Mathematical modelling of flows and discrete phase behaviour in a V‐shaped tundish

In steelmaking processes, various efforts are made in order to enhance steel cleanness. Among other approaches, the volume of the tundish has been increased and flow‐controlling devices are used. The extended mean residence time of steel in the tundish leads to an improved inclusion separation. In the present study, the degree of inclusion separation in different tundish configurations is determined through numerical modelling. Flows in the tundish has been calculated under isothermal and non‐isothermal conditions. The numerical model is based on a Euler Lagrange approach. The flow and the temperature field are described through Reynolds averaged transport equations in conjunction with a turbulence model.     

Two-fluid simulation on the mixed convection flow pattern in a nonisothermal water model of continuous casting tundish

A transient two-fluid model is applied to simulate fluid flow and heat transfer in a nonisothermal water model of continuous casting (CC) tundish. The original liquid in the bath is defined as the first fluid, and the inlet stream, with the temperature variation, is defined as the second fluid. The flow patterns and heat transfer are predicted by solving the three-dimensional (3-D) transient transport equations for each fluid. The results predicted by the two-fluid model make the effect of natural convection more clear compared with the generally used single fluid model k-ɛ turbulence model.     

Transient steel quality under non-isothermal conditions in a multi-strand billet caster tundish: part II. Effect of a flow-control device

A mathematical model was built to simultaneously analyse the effects of non-isothermal conditions and flow-control device on steel quality in a real steelmaking tundish. Liquid steel was used as the operating liquid with a step-input of 23° in a full-scale delta-shaped multi-strand billet caster tundish fitted with a standard impact pad (SIP). The changes in flow pattern and temperature fields of liquid steel in the tundish under isothermal, step-up and step-down conditions were thoroughly studied. Similar to the case of a bare tundish, buoyancy effects were seen to dominate at regions away from the ladle shroud. The presence of SIP modified the flow patterns and resulted into markedly different values of RRI as compared to bare tundish. Finally, the calculated results were qualitatively compared to results obtained from a real steelmaking tundish.     

Modeling flows and mixing in steelmaking ladles designed for single- and dual-plug bubbling operations

Through solutions of appropriate forms of the Navier-Stokes equation, the intermixing of fluid within gas-stirred ladles, with asymmetric single and multiporous plugs, can be modeled quite satisfactorily. In this study, mixing behavior and mixing mechanisms are analyzed as a function of porous plug location, tracer injection point, and ladle monitoring point. It is shown that off-centered bubbling gives the most consistent results in terms of minimizing mixing times, since angular momentum intermixes fluid across the width of a ladle. Comparisons between mathematical and experimental data are presented. Formerly Postdoctoral Fellow, McGill Metals Processing Center, McGill University     

Mathematical simulation and physical modeling of unsteady fluid flows in a water model of a slab mold

Fluid flow of water in a model of a slab caster has been simulated using the large eddy simulation (LES) computational approach, and the simulated results are compared with experimental measurements performed using digital particle image velocimetry (DPIV) techniques. Simulation results agree acceptably well with the experimental measurements of instantaneous velocity fields. Flow patterns change with time as a consequence of the vertical oscillation of the jet core. These oscillations are originated by the residual Reynolds stresses that characterize turbulent flows. The asymmetry of fluid flows caused by these stresses provides biased flows. Thus, turbulence originates natural biasing effects without the influence of other operating factors such as the slide gate opening, gas bubbling, or inclusions clogging of the submerged entry nozzle (SEN). Instantaneous velocities follow periodical behaviors with time whose frequencies increase with increases of flow rate of liquid. Periodical flow changes originate velocity spikes, at some given casting speed, which are physically and mathematically identified. These sudden changes of fluid velocities are responsible of unsteady phenomena associated with fluid dynamics during steady operations of the mold.     

Investigation of transient fluid flow and heat transfer in a continuous casting tundish by numerical analysis verified with nonisothermal water model experiments

The tundish process is complicated due to the periodic nature of its operation during the changing of ladles, which makes it both a transient and nonisothermal process. A nonisothermal water model, with temperature variations in the inlet stream, is described in this article. A three-dimensional (3-D) transient mathematical model to simulate the fluid flow and heat transfer in this water model is also introduced. From the experimental and numerical results, it is shown that there is a significant thermal buoyancy force contributing to the flow in this nonisothermal water model.     

采用DEM-CFD组合模型研究高炉炉身煤气喷吹时炉内气固流动的动力学行为

为减少钢铁厂CO2排放,必须降低焦比。现在高炉炉身喷吹还原气被认为可降低焦比。但炉身喷吹煤气的效果由其在高炉内的穿透性决定。解析高炉炉身喷吹煤气的行为,可有效评价其在实际高炉中的效果。采用DEM-CFD组合模型研究了高炉炉身喷吹煤气的气固流动力学行为。考虑到气固间相互作用,采用DEM模型模拟炉料的准确分布。根据模拟结果,喷吹煤气的流动行为受填充床的透气性制约,且气体的穿透效果被限定在特定区域。除喷吹风口区域外,炉身等压面近似为水平面。喷吹煤气的流速对其在高炉内的穿透性有一定影响。然而,喷吹煤气所占横截面的面积与常规风口和炉身附加风口煤气量的比值相对应。炉身煤气喷吹被认为是控制炉身热流比的有效方法,但其难以与上升气流立刻混合。根据期望目标,需慎重选择喷吹位置。该结果可应用于顶煤气循环等新工艺的设计。     

Viscoplastic constitutive model of a nickel-based superalloy under multiaxial loading conditions

Based on Chaboche constitutive model, a viscoplastic constitutive model of nickel-based alloy under multiaxial loading is proposed by introducing Lemaitre damag...