In present 92.8% of world steel production is casted on continuous casting machine. The key phase of continuous casting is tundish. Beside of refining effect of slag phase also steel flow in tundish is very important factor. The main causes for inclusion formation and contamination of the melt include reoxidation of the melt by air and carried over oxidizing ladle slag, entrainment of tundish and ladle slag, and emulsification of these slags into the melt. These causes are due to generation of turbulence in the melt. Although turbo stop lowers the turbulence in some extent. But it is not capable of totally decrease of turbulence specially during lowering of metal bath at the time of ladle exchange operation, cause contamination of the steel melt in tundish. So in the present work it has been focused to develop a novel shroud which have significant role to supply of steel from ladle to tundish at slow rate to avoid turbulence, emulsification and formation of slag eye in tundish to produce quality steel in a sustained manner.
The HOLLOW JET NOZZLE (HJN) is a heat exchanger used for the removal of superheat from molten steel between tundish and mold. It is a relatively new technology, developed by CRM, Belgium, through engineering the design of the conventional submerged entry nozzle (SEN) in continuous casting. In the present study, fluid-flow phenomena in a HJN system were investigated experimentally via a 0.23-scale water model, designed and operated on the basis of a Froude scaling criterion. Parallel to such, numerical simulation was carried out via FLUENT 6.1 embodying a turbulent, VOF-based, multiphase flow calculation procedure. These, in general, indicated that the incoming liquid, following its impingement on the solid baffle, spreads radially and flows down as a thin liquid film along the wall of the HJN. A large number of experiments were carried out to determine the radial spread of the impinging water jet and its point of attachment on the wall of the HJN as a function of volumetric flow rate, baffle geometry and dimensions, diameter of HJN, etc. These indicated that baffle geometry and dimensions together with the diameter of the HJN influence the point of attachment (or the corresponding ''attachment distance'') most. It was demonstrated that attachment distance and the associated contact area between the flowing liquid and HJN wall can be considerably improved by appropriately modifying the currently employed baffle design. Such experimental findings were corroborated well by the FLUENT-based numerical procedure, which was in general able to capture the intricacies of film flow in the HJN system reasonably accurately. In addition to these, simplified models for attachment distance and film thickness have been developed and proposed for axisymmetrical HJN operation. Based on such, a relatively simple differential heat flow model has been developed for prediction of melt temperature in an industrial HJN system. It is demonstrated that in the absence of any elaborate numerical computation, the simplified models developed in this study provide a reasonable basis for engineering calculations in the axisymmetrical HJN system.
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