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Title:High fidelity numerical investigations of tailored magnetic fields for defect reduction in continuous casting of steel
Author(s):Singh, Ramnik
Advisor(s):Vanka, Surya Pratap; Thomas, Brian G.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Continuous Casting
Mold Flow
Large Eddy Simulation (LES)
Electromagnetic Braking (EMBr)
Ruler EMBr
Flow-Control-Mold EMBr, Scaling Criterion
Abstract:In the Continuous Casting (CC) process, defects are created when the inclusions are entrained deep into the strand and are entrapped in the solidifying shell. Both the creation and entrapment of inclusions are a function of transient fluid flow behavior in the mold along with the inclusion properties. This thesis focuses on better understanding of mold flow with Electromagnetic Braking (EMBr), which is an attractive method due to its non-intrusive nature. EMBr greatly influences turbulent flow in the continuous casting mold and its transient stability, which affects level fluctuations and inclusion entrainment. Large eddy simulations are performed to investigate these transient flow phenomena using an accurate numerical scheme implemented on a Graphics Processing Unit (GPU). Two arrangements of EMBr are studied in this work, the single ruler EMBr configuration and the “Flow-Control-mold” or “FC-mold” EMBr configuration. The effects of each configuration are studied by comparing with corresponding cases without any applied magnetic field. The in-house developed CFD model is first applied to simulate experiments conducted on a 1/6th scale physical caster model with GaInSn as the low-melting conducting liquid and is then applied to the corresponding full-size caster to evaluate scaling criterion in the presence of applied magnetic fields. The mold flow has a classic “double-roll” flow pattern without the application of any magnetic fields. The application of ruler EMBr over the nozzle deflects the jets upwards and increases the top surface velocity. With insulated walls, the mold flow has large scale fluctuations and an unstable flow pattern. This instability is completely damped by using conducting side walls. These flow patterns are matched well in the corresponding real-size caster by maintaining only the Stuart number. However, to match the level fluctuations between the two casters, a Froude number ratio based scaling technique is applied. The computational model is next applied to study transient flow in a real commercial steel caster and the computed results are compared with nail board measurements. Without magnetic fields, this caster exhibits a “double-roll” flow pattern, but with transient unbalanced flow oscillations, producing unbalanced flows and vortices which might be detrimental to steel quality. The application of a FC-mold EMBr damps this unbalanced flow behavior and also reduces surface velocity, surface level fluctuations, and variations in the surface level profile. Although this might lessen slag entrainment problems, the small surface velocities resulting from this strong magnetic field across the top surface may make the meniscus prone to freezing and associated surface defects.
Issue Date:2013-08-22
Rights Information:Copyright 2013 by Ramnik Singh. All rights reserved.
Date Available in IDEALS:2013-08-22
Date Deposited:2013-08

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