Two-fluid simulation on the mixed convection flow pattern in a nonisothermal water model of continuous casting tundish
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I. INTRODUCTION
THE tundish, working as a buffer and distributor of liquid steel between the ladle and continuous casting (CC) molds, plays a key role in affecting the performance of the CC machine, solidification of liquid steel, quality, and productivity. Liquid steel flow and temperature distribution are the basic factors governing operation of the tundish process. A multidimensional mathematical model based on computational fluid dynamics (CFD) is nowadays considered as a useful tool to analyze these transport processes in the tundish. There have already been significant efforts in the field of mathematical modeling of transport processes in the tundish. Most of these works have considered steady-state flow conditions and a forced convection system.[1–4] Hence, the momentum equations and the equations for conservation of thermal energy were solved separately. These mathematical modeling results provide useful information for understanding and improving the tundish process. However, according to the characteristics of the tundish process, the temperature of the steel in the tundish varies due to the temperature variation of inlet stream, heat loss to the surroundings, and/or external heating and cooling operations. Thus, it is obvious that there is a nonisothermal and transient state in the actual tundish process. Hence, in the authors’ previous study,[5] a nonisothermal water model was designed to study the convection pattern of liquid steel flow in the tundish. It was concluded that the convection of liquid steel in the tundish is controlled by a mixed convection pattern, that is, the combination of natural convection and forced convection. Variation of steel temperature will have a significant effect on the overall fluid flow behavior. Hence, a more integrated mathematical model is necessary, which allows for coupling of fluid flow and heat transfer under three-dimensional (3-D), transient, nonisothermal conditions. There are several publications focusing on this topic.[6–9] The single fluid model with k-« turbulence model is the generally used method to simulate the flow and heat coupling D.Y. SHENG, Research Engineer, and LAGE JONSSON, Professor and Manager, Casting and Flow Simulation, are with the Process Metallurgy Department, MEFOS, S-97125 Lulea, Sweden. Manuscript submitted August 20, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
phenomena in the tundish. In the authors’ previous research,[10] using the single fluid model, it can be found that the predicted fluid flow and heat transfer were in reasonable agreement with the measurements. However, comparing the magnitudes of temperature variation, the overprediction of heat transfer was shown, especially in the transition region of the bulk liquid. This indicated that the k-« turbulence model overestimated the turbulent intensity in the transition region, leading to too high a prediction of conductive heat transfer. This phenomenon was also described by Ilegbusi,[11] who applied a two-fluid model in order to capture the turbulence of the tundish. Th
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