In order to optimize steel flow and maximize the contact time of the inclusions with the slag layer inside the tundish, a proper flow-control arrangement must be designed, considering the shape, the dimensions of the prototype, and the plant operating conditions of the tundish. Physical and mathematical modeling has been used in this study, in a complementary fashion, to evaluate the influence of turbulence-inhibiting devices on the velocity fields, tracer dispersion, small-and large-particle trajectories, flow-pattern characteristics, and grade changes in a large-volume tundish. From the water model and mathematical simulation results, a flow-control system with the best performance was identified; this system must contribute to improving the productivity and cleanliness of the continuous-cast steel.

Water modeling and mathematical simulation techniques were used to study the melt flow under the influence of turbulence inhibitors in a multistrand bloom caster tundish. Three different cases were studied: a bare tundish (BT), a tundish with two pairs of baffles and a waved impact pad (BWIP), and a tundish equipped with turbulence inhibitor and a pair of dams (TI&D). Chemical mixing of tracer turbulence diffusion was also simulated and compared with actual experimental results. The TI&D arrangement showed an improvement of the fluid flow characteristics, yielding better tracer distribution among the outlets, lower values of back mixing flow, and higher values of plug flow. A mass transfer model coupled with k-turbulence model predicted acceptably well the experimental chemical mixing of the tracer in the water model. The water modeling and the numerical simulation indicated that the TI&D arrangement retains the tracer inside the vessel for longer times, increasing the minimum residence time. These results encourage the use of turbulence-inhibiting devices in bloom and billet casters, which pursue excellence in product quality.

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en Ingenierfa Mscaruoa, Morelia Mich., Mexico.Non-metallic inclusion removal from liquid steel in a tundish is studied using two-phase flow modelling by Particle Image Velocimetry (PIV) techniques and mathematical simulation. The removal efficiency is studied as a function of Flow Control Devices (FCD) arrangements inside the tundish, gas bubbling and mass flow rate. The mathematical two-phase model includes an Eulerian-Eulerian approach for the gasliquid system and a Lagrange approach for the solid particles trajectories. The validation of this model was acceptably proved through PIV measurements and colour tracer experiments in a two-phase water model. The removal efficiency of the tundish in the cases of gas bubbling becomes independent of particle size and FCD arrangements. An increase of mass flow rate decreases the particle mean residence time in the tundish and therefore the removal efficiency. Under the same conditions coupling-uncoupling phenomena of solid particles from the liquid flow depends strongly on their response time. Where this phenomena occurs, it is determined that the particle response time in the model goes from 10-5 to 10-3 seconds for particle size ranging from 20 to 160 11m, respectively; this transition is dependent on particles size and mass flow rate.

Fig. 13. Bubble plume structure; a) physical modeling and b) numerical simulation.

The flow patterns prevailing at the free-surface in a water model of a slab continuous casting mold using several water flow rates and entry nozzle submergence depths are experimentally and numerically studied in this work. The experimental study was carried out using an one-third scale cold water model, constructed in accordance with the Froude similarity criterion. Water level measurements were carried out with ultrasonic distance sensors and recorded in a computer. Numerical simulations were made with a commercial computational fluid dynamics software. It was found that free-surface oscillations are composed by several periodic components. There exists a fundamental periodic frequency of 1.2 Hz. Besides, there exist two other frequencies of 1.8 and 2.1 Hz whose contribution to the free surface dynamic behavior depend on the spatial position and on the process parameters, namely, the volumetric flow rate and the submerged entry nozzle (SEN) submergence depth. In accordance with the obtained results, several recommendations about operating policies of actual industrial casters are made.KEY WORDS: free surface velocity; mold flow; power density spectrum; slab continuous casting; submerged entry nozzle.well-known Navier-Stokes equations, which in vectorial form are expressed as follows 8,10) Given that the experiments are carried out isothermally, the energy equation is not considered. The K-e turbulence model was selected for mathematical modeling, which is described by the following expressions: ... (4) In the above equations K is the turbulent kinetic energy, e is dissipation rate of K. s K , s e , C 1 and C 2 are constants whose values are 1.0, 1.3, 1.44 and 1.92 respectively.8) The fluid viscosity must be corrected for turbulence in the Navier-Stoke equations employing an effective viscosity m eff ϭm l ϩm t , where m l is the laminar viscosity and m t is the turbulent viscosity. The latter can be determined as follows: (5) where C m ϭ0.09 is a constant. The boundary conditions in the mathematical model were those recommended by Thomas et al. 8) and are as follows: Inlet turbulence parameters at the inlet were Kϭ0.044 m 2 s Ϫ2 and eϭ1.00 m 2 s Ϫ3. At the outlet, the boundary condition was fixed in such a way that the mass balance was satisfied.A commercial CFD software was employed for numerical solving of the above mathematical model. A two-dimensional mesh with 32 500 nodes was created with a time step of 0.001 s. A personal computer with 1 GB of RAM memory and 3.0 GHz CPU was utilized for the numerical simulations. A run for 70 s of real time required a CPU time of approximately 5 h. In order to track the free surface profile, two-phase flow was considered and the Volume-of-fluid (VOF) model 10) was chosen for tracking of the air-water interface. Physical ModelingA plastic one-third scale water model was designed and constructed in accordance with the Froude similarity criterion. Froude criterion guarantees that the water model is similar to the industrial caster mold from the geometrical and dynamical...

Transient fluid flow behavior in a tundish with two different arrangements, a bare tundish and a tundish using flow control devices, was studied using physical modeling and a mathematical model. The study places special emphasis on buoyancy effects, particularly transient buoyancy effects due to step change in inlet temperature. For the bare tundish case, the inertial forces are strongly dominant, while in the arrangement using flow control devices, tundish with turbulence inhibitor and low dams, the buoyancy forces are dominant. The results were compared to those representing the real behavior, considering temperature variations, for each tundish arrangement. This comparison made possible the determination of the probable implicit error that could be present in the estimation of the fluid flow characteristic behavior used for the design of the tundish geometry and flow control devices when the temperature variations are not considered.

A mathematical model was developed to study effects of the vortex and the short circuit flow phenomena during tundish operation on the inclusion removal for a wide range of particle diameters. The model was solved using FLUENT® commercial software; for the particle tracking the Lagrangian discrete phase model was employed. Even when the vortexes drag about 50% of the inclusions, the most detrimental phenomenon for inclusion removal is the short circuit flow. It is important to stress that for the global inclusion behavior the removal rate decreases as the tundish level increases. It can be concluded that when increasing the tundish capacity without any flow control device adjustment, the steel cleanliness is deteriorated significantly.