A new design of a ladle shroud, obtained through water modeling, that controls turbulence of the entry jet in continuous casting tundishes is proposed. Particle Image Velocimetry (PIV) measurements indicate that this design decreases the impact velocity on the tundish bottom to close to 1/3 of that provided by a conventional ladle shroud. This achievement is due to a swirling jet that promotes a recirculatory flow in the horizontal planes of the tundish. The swirling effects help to dissipate the turbulence energy of the jet before it impacts the tundish bottom making possible decreases of fluid velocities that impact the back and front walls of the tundish. Turbulence models like k -e, k -w and RSM were applied to simulate the experimental PIV measurements of velocities in the fluid flow. Only the RSM model yielded results that agree remarkably well with the experimental determinations. These results make possible to avoid the employment of flow control devices such as dams, weirs, turbulence inhibitors and the like in tundishes.KEY WORDS: tundish; ladle shroud; turbulence dissipation; PIV; mathematical models. and a density of 1 030 kg/m 3 was fed through a syringe in the upper part of the ladle shroud. By following the tracks of these particles, using a Particle Image Velocimetry (PIV) equipment, velocity fields of water were recorded. Particle tracks were recorded by a Coupled Charged Device (CCD) equipped with a lens of depth field. All signals are processed in a PC; using the cross correlation technique and Fast Fourier Transforms they are converted into fluid velocities. [23][24][25] Figure 2 shows a scheme of the experimental setup. Two ladle shrouds were investigated the first one is of a conventional (LS) design and its dimensions are shown in Fig. 3(a) the second is a swirling ladle shroud (SLS) which consists of central pipe with three intermediate chambers that work as a brake of fluid velocity and an upper blade whose function is to start a swirling motion of the fluid all through the shroud length up to its tip. The tip of the shroud has bell shape to reinforce the braking effect on the fluid which flows into the tundish. Water flow rate was 5.83ϫ10Ϫ4 m 3 /s corresponding to 3.8 tons of liquid steel/min in the current tundish, according to the Froude criterion. This flow was maintained constant for this work. Theory of Turbulence ModelsThe most commonly used turbulence model is that devised by Jones and Launder 28) and known as k-e, it has many advantages; its concept is simple, is implemented in very commercial codes and it has demonstrated capability to simulate correctly many industrial processes like combustion, 27) fluid flow in tundishes 15,16) and multiphase flows 28) among many other applications. Nevertheless, it fails to provide reliable results of swirling flows and highly strained angular velocities of rotating flows.30) Since we are dealing here with a complex swirling flow two other turbulence models were tried; the k-w model of Wilcox 29) and the Reynolds Stress model (RSM) which ...

Flow of steel in a one-strand slab tundish equipped with a turbulence inhibitor (TI) and a transversal gas bubbling curtain was studied using mathematical simulations, PIV measurements and Residence Time Distribution (RTD) experiments in a water model. The use of a bubbling curtain originates two recirculating flows, upstream and downstream at each of its sides. The first one meets, at some point along the tundish length and close to the bath surface, the downstream that is driven by the TI. After, free shear stresses provided by the upstream make the downstream be directed toward the tundish bottom forming a bypass flow. At the other side, in the outlet box, there is strong recirculating flow which impacts the end wall and goes directly toward the outlet. Two-phase flows simulated mathematically matched experimental flow fields measured with PIV measurements. Tundish performance for inclusions flotation is maximized when only the TI is used followed by using only the bubbling curtain. Increases of gas bubbling flow rate increase the mixing processes in the tundish according to the RTD determinations.

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Fluid flow dynamics during ladle drainage operations of steel under isothermal and nonisothermal conditions has been studied using the turbulence shear stress transport k-model (SST k-) and the multiphase volume of fluid (VOF) model. At high bath levels, the angular velocity of the melt, close to the ladle nozzle, is small rotating anticlockwise and intense vertical-recirculating flows are developed in most of the liquid volume due to descending steel streams along the ladle vertical wall. These streams ascend further downstream driven by buoyancy forces. At low bath levels, the melt, which is close to the nozzle, rotates clockwise with higher velocities whose magnitudes are higher for shorter ladle standstill times. These velocities are responsible for the formation and development of a vortex on the bath free surface, which entrains slag into the nozzle by shear-stress mechanisms at the metal-slag interface. The critical bath level or bath height for this phenomenon is 0.35 m (in this particular ladle design) for a ladle standstill time of 15 minutes and decreases with longer ladle standstill times. At these steps, the vertical-recirculating flows are substituted by complex horizontal-rotating flows in most of the liquid volume. Under isothermal conditions, the critical bath level for vortex formation on the melt free surface is 0.20 m, which agrees very well with that determined with a 1/3 scale water model of 0.073 m. It is concluded that buoyancy forces, originated by thermal gradients, as the ladle cools, are responsible for increasing the critical bath level for vortex formation. Understanding vortex mechanisms will be useful to design simple and efficient devices to break down the vortex flow during steel draining even at very low metal residues in the ladle.

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