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The aims of the present study are to predict and improve inclusion separation capacity of a six strand tundish by employing flow modifiers (dams and weirs) and to assess the influence of inclusion properties (diameter and density) together with velocity of liquid steel at the inlet gate on the inclusion removal efficiency of a six-strand tundish. Computational solutions of the Reynolds-Averaged Navier-Strokes (RANS) equations together with the energy equation are performed to obtain the steady, three-dimensional velocity and temperature fields using the standard k-ε model of turbulence. These flow fields are then used to predict the inclusion sepapration by numerically solving the inclusion transport equation. To account for the effects of turbulence on particle paths a discrete random walk model is employed. It was observed that with the employment of flow modifiers, the inclusion separation capacity of tundish increases without any large variation in the outlet temperatures. It is shown that inclusion properties and velocity are important parameters in defining the operating conditions of a six-strand tundish.

Continuous casting processes dominate steel production the world over due to their significant advantages, i.e., considerable energy saving, small waste material, improved labor productivity and reduced pollution. Tundish is the final and most important unit of a continuous casting process in which the final processing with liquid metal can be done before it reaches the mould. Since it is the final unit, tundish serves as a reservoir for the mold which also helps to avoid splashing and removal of inclusions particles resulting from various metal air interactions together with other impurities present in the molten steel.

A large number of studies have been reported in the literature dealing with the physical and mathematical modeling of fluid flow condition together with the inclusion motion behavior inside a tundish for different tundish geometries and flow conditions. Raghavendra et al. [

Yang et al. [

Lei and He [

Tripathi and Ajmani [

Morales et al. [

Zheng and Zhu [

Most studies reported in the literature deal with singlestrand tundishes. The present study deals with a multistrand tundish. Such tundishes are being increasingly used in continuous casting processes. Many studies reported in the literature use the residence time curves to predict the inclusions behavior inside the tundish. In the present study Lagrangian motion of inclusions is tracked and it provides a good insight into the behavior of tundish. The geometry of the tundish should be such that it separates maximum percentage of inclusions present in the molten steel. Being lighter than steel, inclusions can be removed by trapping at the top surface. The use of flow modifiers is reported to promote the flow field towards the top surface which increases the inclusion removal efficiency of a tundish. The arrangement of flow modifiers used for enhancing inclusion separation efficiency should be such that temperature and percentage of inclusion at each outlet are nearly equal to produce the same quality of steel from each strand. Moreover, tundish should be subjected to modification only at the interior geometry and at the same time, it should not be expensive to fabricate.

With continuous research efforts over the last decade, computational fluid dynamics (CFD) has now become an effective tool for the design of steel tundishes. In the present study, 3-D, turbulent flow field in a six-strand trough type tundish is investigated using the standard k-ε model of turbulence. The finite volume based commercial software FLUENT 6.3.26 is used for performing the simulations. The flow fields thus obtained are used to predict the inclusion separation by numerically solving the inclusion transport equation, considering its drag and buoyancy forces. To simulate the chaotic effect of turbulent eddies on particle motion a discrete random walk model is used. The effects of flow modifiers, i.e., dam and weir, together with their height and molten steel stream velocity at the inlet gate on the inclusion motion (for different particle size and density) and outlet temperature of liquid steel have been investigated. The geometry of the multi-strand tundish is described in Section 2. The governing equations, turbulence model and boundary conditions are presented in Section 3. The code validation and results are presented in Section 4 followed by conclusions.

The geometry of multi-strand tundish considered in the present study is taken from the study reported Merder et al. [_{1} = 2785 mm, L_{2} = 2700 mm, L_{3} = 300 mm, L_{4} = 500 mm, L_{5} = L_{6} = 1000 mm, W_{1} = 1040 mm, W_{2} = 850 mm, W_{3} = 640 mm, W_{4} = 450 mm and steel bath height H = 740 mm. The inlet and outlet diameters of the gate are taken as 66 mm and 14 mm, respectively [

^{3}, specific heat = 821 J/kg·K, thermal conductivity = 30.5 W/m·K and viscosity = 0.007 kg/m·s.