A Model Study of Inclusions Deposition, Macroscopic Transport, and Dynamic Removal at Steel–Slag Interface for Different Tundish Designs CHAO CHEN, PEIYUAN NI, LAGE TORD INGEMAR JONSSON, ANDERS TILLIANDER, GUOGUANG CHENG, and PA ¨ R GO ¨ RAN JO ¨ NSSON This paper presents computational fluid dynamics (CFD) simulation results of inclusions macroscopic transport as well as dynamic removal in tundishes. A novel treatment was implemented using the deposition velocity calculated by a revised unified Eulerian deposition model to replace the widely used Stokes rising velocity in the boundary conditions for inclusions removal at the steel–slag interface in tundishes. In this study, the dynamic removal for different size groups of inclusions at different steel–slag interfaces (smooth or rough) with different absorption conditions at the interface (partially or fully absorbed) in two tundish designs was studied. The results showed that the dynamic removal ratios were higher for larger inclusions than for smaller inclusions. Besides, the dynamic removal ratio was higher for rough interfaces than for smooth interfaces. On the other hand, regarding the cases when inclusions are partially or fully absorbed at a smooth steel–slag interface, the removal ratio values are proportional to the absorption proportion of inclusions at the steel–slag interface. Furthermore, the removal of inclusions in two tundish designs, i.e., with and without a weir and a dam were compared. Specifically, the tundish with a weir and a dam exhibited a better performance with respect to the removal of bigger inclusions (radii of 5, 7, and 9 lm) than that of the case without weir and dam. That was found to be due to the strong paralleling flow near the middle part of the top surface. However, the tundish without weir and dam showed a higher removal ratio of smaller inclusions (radius of 1 lm). The reason could be the presence of a paralleling flow near the inlet zone, where the inclusions deposition velocities were much higher than in other parts. DOI: 10.1007/s11663-016-0637-6 Ó The Minerals, Metals & Materials Society and ASM International 2016 I. INTRODUCTION THE removal of non-metallic inclusions (hereafter inclusions) in continuous casting tundishes has been widely studied via (1) water modeling experiments, (2) analyses of industrial samples, (3) empirical, semi-em- pirical, analytical, and phenomenological models, and (4) computational fluid dynamics (CFD) simulations. Traditionally, a tundish played a role as a ‘‘filter’’ for the removal of larger inclusions. [1] Many water model experiments [2–10] and the correspond- ing CFD simulations [8–10] have verified that the larger particles are easy to float up to the water surface in a tundish. However, the deficiencies of water model exper- iments are (1) the size of the buoyant particles is usually bigger than 20 lm, which cannot be applied to study the small sizes of inclusions in a steel system; (2) in some models, the surface is a free surface, i.e., water was exposed to the air; this approach fails to interpret the influence of friction of the tundish slag on the flow of liquid steel; and (3) the lack of ‘‘thermodynamic similarities’’ [11] in comparison to a steel-inclusion system. These deficiencies may hinder the understandings of inclusion removal to a tundish slag with respect to the small size inclusions, deposition at the turbulent boundary layers at steel–slag interface, and the wetting of inclusions by slag, respectively. CFD simulations of the inclusions motion and removal in tundishes have widely been studied by Lagrangian approaches [8–30] and by Eulerian approaches. [1,17,29,31–38] The earliest publications on the two approaches could be dated back to Debroy and Sychterz [12] in 1985 and Tacke and Ludwig [31] in 1987, respectively. However, the inclusions deposition through the boundary layers (here- after BL) was often neglected in CFD model studies. For CHAO CHEN, formerly Ph.D. Student with the Unit of Process, Department of Materials Science and Engineering, KTH-Royal Institute of Technology, Brinellva¨gen 23, 100 44 Stockholm, Sweden, and also Ph.D. Student with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, 100083 Beijing, P.R. China, is now Lecturer with the Department of Metallurgy, College of Materials Science and Engineering, Taiyuan University of Technology, Yingze West Street No. 79, Taiyuan 030024, Shanxi, P.R. China. Contact e-mail: chenchao@tyut.edu.cn PEIYUAN NI, Postdoctoral Researcher, ANDERS TILLIANDER, Associate Professor, and PA ¨ R GO ¨ RAN JO ¨ NSSON, Professor, are with the Unit of Process, Department of Materials Science and Engineering, KTH-Royal Institute of Technology. LAGE TORD INGEMAR JONSSON, Professor, is with the Unit of Process, Department of Materials Science and Engineering, KTH-Royal Institute of Technology, and also with the Division of CBRN Defence and Security, FOI, Swedish Defence Research Agency, 901 82, Umea˚, Sweden. GUOGUANG CHENG, Professor, is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. Manuscript submitted May 31, 2015. Article published online March 16, 2016. 1916—VOLUME 47B, JUNE 2016 METALLURGICAL AND MATERIALS TRANSACTIONS B