Inertial and buoyancy driven water flows under gas bubbling and thermal stratification conditions in a tundish model
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3/3/04
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Inertial and Buoyancy Driven Water Flows under Gas Bubbling and Thermal Stratification Conditions in a Tundish Model A. VARGAS-ZAMORA, R.D. MORALES, M. DÍAZ-CRUZ, J. PALAFOX-RAMOS, and J. DE J. BARRETO-SANDOVAL Steel flow dominated by inertial and buoyancy flows under gas bubbling and thermal stratification conditions, in a one-strand tundish, was studied using a 2/5 scale water model. The use of a turbulence inhibitor yields plug flow volume fractions well above 40 pct for a casting rate of 3.12 tons/min under isothermal conditions. Small flow rates of gas injection (246 cm3/min), through a gas curtain, improved the fluid flow by enhancing the plug flow volume fraction. Higher flow rates originated an increase of back-mixing flow, thus forming recirculating flows in both sides of this curtain. Step inputs of hot water drove streams of this fluid toward the bath surface due to buoyancy forces. A rise in gas flow rate led to a thermal homogenization in two separated cells of flow located at each side of the gas curtain. Step inputs of cold water drove streams of fluid along the tundish bottom. Use of the gas curtain homogenized the lower part of the tundish as well as the upper part of the bath at the left side of the curtain. However, temperature at the top corner of the tundish, in the outlet box, remained very different than the rest of the temperatures inside this tundish. High gas flow rates (912 cm3/min) were required to homogenize the bath after times as long as twice the mean residence time of the fluid. Particle image velocimetry (PIV) measurements corroborated the formation of recirculating flows at both sides of the gas curtain.
I. INTRODUCTION
THERMAL stratification in tundishes arises from the corresponding thermal stratification of steel in the ladle, which promotes a varying ladle stream temperature. Thermal stratification in tundishes is also promoted during ladle changes when hot or cold steel is introduced in the tundish promoting the generation of buoyancy forces that match or even surpass inertial forces. Buoyancy forces then radically change the fluid flow pattern inside the tundish when it is compared with the flow under steady-state and isothermal conditions. Mathematical simulations of transport phenomena involved in thermal stratification in tundishes have been reported and discussed in various references. Joo et al.[1,2] simulated heattransfer and particle dispersion in tundishes. Barreto et al.[3,4] provided information of fluid flow in tundishes using water model and mathematical simulations. Barron et al.[5] characterized, through water modeling and mathematical simulations, the thermal stratification in plasma-heated tundishes. Chakraborty and Sahai[6,7] simulated the effects of varying ladle stream temperature on steel flow in tundishes and reported delayed radical changes of fluid flow pattern due to buoyancy forces. More recently, Morales and co-workers[8,9,10] reported mathematical simulations of thermal stratification also due to varying ladle stream te
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