Flow Driven by an Archimedean Helical Permanent Magnetic Field. Part II: Transient and Modulated Flow Behaviors
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ion at the solidification front play very important roles during the solidification process. The resulting heat, mass, and solute transport phenomena affect not only the movement of the solid–liquid interface, but also the global heat distribution. These changes affect the morphology of the solid–liquid interface as well as the micro/macrostructure, micro/macrosegregations, and freckling of the materials[1–3] and thus the mechanical properties of the materials. However, elucidating the mechanism of this process has been a key challenge in the solidification field, leading Professor Guthrie to the question, ‘‘Fluid Flows in Metallurgy-Friend or Foe?’’[4] Magnetic fields and electromagnetic forces are commonly used in industrial applications for nonintrusive stirring[5,6] and flow control[7,8] of a solidifying melt. In general, different magnetic fields are suitable, such as BO WANG, Ph.D. Candidate, and XIAODONG WANG, Professor, are with the College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 101408, China. Contact e-mails: [email protected], [email protected] YVES FAUTRELLE and JACQUELINE ETAY, Professors, are with the Grenoble Institute of Technology/SIMAP/EPM, PHELMA, BP75, 38402 St Martin d’He`res Cedex, France. XIANZHAO NA, Professor, is with the State Key Laboratory of Advanced Steel Processing and Products, Central Iron and Steel Research Institute, Beijing 100081, China. FLORIN BALTARETU, Professor, is with UTC Bucharest, bd. Pache Protopopescu, Bucharest, Romania. Manuscript submitted April 27, 2016. Article published online August 15, 2016. 3476—VOLUME 47B, DECEMBER 2016
rotating (RMFs), traveling (TMFs), and pulsating magnetic fields and combinations of these three. For a finite liquid melt enclosed in a cylindrical column, the imposition of an RMF can generate an essentially swirling flow, which is often called the primary flow. Because of the restricting effect of the sidewalls, this primary flow produces a secondary (meridional) flow in the form of two counter-rotating, toroidal vortices[9] as a result of the Ekman pumping effect. Although the amplitude of the secondary flow is several times smaller than that of the primary flow, the convective transports in the vertical and radial directions are mainly achieved by the former because the primary flow consists mainly of a nearly rigidly rotating core.[9] TMF causes traction in the direction of its wave vector. The TMF-driven flow returns through the central part, where the axial body force is weaker, and consequently, there is a meridional circulation in the form of a single toroidal vortex.[10,11] For applications of forced convection driven by magnetic fields during the solidification process, each field type has advantages and disadvantages. RMF-driven convection promotes the columnar to equiaxed transition (CET) in growth and provokes a distinct grain-refining effect.[12] Unfortunately, RMF-driven flow also causes adverse side effects such as macrosegregations.[13–15] TMF-driven flow has been gai
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