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Mixing phenomena in a six strand billet caster tundish has been studied by numerically solving the Navier Stokes equations along with the species concentration equation in a boundary fitted coordinate system comprising the geometry of the tundish. The solution of the species concentration equation has been utilized to compute the mix, dead and plug volume of the tundish under different flow conditions. The numerical procedure and solution algorithm has been first verified by comparing the numerically obtained residence time distribution curve, which agree well with that of the experiments done for a single strand bare tundish by Singh and Koria. 44) It has been observed that the ratio of the mix to dead volume for the six strand tundish has a maximum value for a particular position of the outlets. At that particular position of the outlets (where mixing is best), an APB is placed on the bottom of the tundish surrounding the incoming inlet jet and the height of the APB has been varied to see the effect on mixing in the tundish. It has been observed that the ratio of mix to dead volume further increases with the use of APB and attains a peak value after which it decreases with the increase of the height of the APB signifying the existence of an optimum APB height. At this optimum height of the APB, the shroud immersion depth was made to change from 0 to 400 mm. It was also observed that there exists an optimum immersion depth of the shroud where the ratio of mix to dead volume still attains another peak signifying still better mixing. However, increasing the immersion depth to higher values spoils mixing significantly.KEY WORDS: billet caster tundish; mixing; mean residence time; advance pouring box; shroud immersion depth.benefit in terms of gaining better mixing in the tundish as discussed in Sec. 3.2 rather than putting dams and weirs. It should be noted here that fixing up dams and weirs in a tundish is a much involved job rather than changing outlet positions, which seem to be rather easier. Moreover on the leeward side of the dams and weirs, there will normally be dead zones which rather spoils mixing in the tundish. So this has been tried in the present work and in addition to this an Advanced Pouring Box (APB) has been put around the inlet jet where it impinges on the bottom plane so that the resulting flow may create better mixing in the tundish. The effect of the height of the APB brings in interesting variations to the flow field and also to the mixing in general. The effect of the shroud immersion depth makes the flow field still benign to mixing, which is normally not found in literature in the present form. So the present study is an effort in this direction. Physical Description of the ProblemThe geometry of the billet caster tundish is shown in Fig. 1a along with the three outlets. The tundish is shown half because of the symmetry about the inlet plane. The depth of the tundish and the bottom pad are 572 and 280 mm respectively with the size of the inlet as 25 mmϫ50 mm and all other dimensions a...

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