Modeling and Measurements of Multiphase Flow and Bubble Entrapment in Steel Continuous Casting
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bbles captured during the continuous casting of steel are a major cause of defects, such as blisters and slivers, in rolled steel products.[1] Ar gas is usually injected at the slide gate or stopper rod to prevent nozzle clogging.[2–4] The jets of molten steel then carry those bubbles through the Submerged Entry Nozzle (SEN) and into the mold cavity region, where they greatly affect the flow pattern, surface level fluctuations, and slag entrainment. Large bubbles captured near the surface can lead to blister defects, such as pencil pipe, after rolling and annealing.[5,6] Furthermore, the moving Ar bubbles collect nonwetting inclusion particles, such as alumina. If such a bubble is captured by the solidifying steel shell, the layer of inclusions covering its surface will lead to large oxide clusters, which cause severe sliver defects in the final product.[7,8] Ar bubbles entering the mold region end up at three locations: (1) some reach the top surface, pass through KAI JIN, Research Assistant, and BRIAN G. THOMAS, C.J. Gauthier Professor, are with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street (MC-244), Urbana, IL, 61801. Contact e-mail: [email protected] XIAOMING RUAN, Senior Researcher, is with the Steelmaking Research Department, Research Institute Baoshan Iron & Steel Co., Ltd., 889 Fujin Rd., Shanghai 201900, P.R. China. Manuscript submitted September 28, 2015. Article published online December 22, 2015. 548—VOLUME 47B, FEBRUARY 2016
the slag layer, and escape harmlessly to the atmosphere; (2) some are captured near the meniscus and lead to surface defects; (3) some are captured deep in the caster and cause internal defects. Many previous works have studied two-phase flow of argon and molten steel in the SEN and mold region of the continuous caster using water models and computational models.[2,7–24] Increasing Ar gas causes increased upward flow near the SEN and tends to reverse the classic double-roll flow pattern to single roll with surface flows away from the SEN toward the narrow face.[10,19,20] Asymmetric, oscillating flow is observed if gas fractions are excessive.[2,25] Computational models of this multiphase flow should be three-dimensional and two-way coupled, as the Ar gas affects the steel flow and vice versa, especially with large gas fractions.[9–11,21] Many researchers have used Eulerian–Eulerian flow models to investigate this two-phase flow problem.[10,18–20,26] Liu et al.[21] recently used inhomogeneous Multiple Size Group (MuSiG[27]) Eulerian models of the gas phase to describe the polydispersed bubbly flow in this process. Flow is affected by the input bubble size distribution. Liu et al. measured Sauter mean diameters (1 to 3 mm) in their physical water model, which are typical of previous measurements.[28] Increasing gas flow generates more and larger bubbles.[2,25,28] Argon bubbles in steel are reported to be larger than air bubbles in water.[21,28] Other models have used Lagrangian descriptions for the argon gas bubbles[9–15,17
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