morales_2005
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morales_2005


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Melt Flow Control in a Multistrand Tundish Using a
Turbulence Inhibitor
R.D. MORALES, J. de J. BARRETO, S. LO´ PEZ-RAMIREZ, J. PALAFOX-RAMOS, and
D. ZACHARIAS
Water modeling and mathematical simulation techniques were used to study the melt flow under the
influence of turbulence inhibitors in a multistrand bloom caster tundish. Three different cases were
studied: a bare tundish (BT), a tundish with two pairs of baffles and a waved impact pad (BWIP),
and a tundish equipped with turbulence inhibitor and a pair of dams (TI&D). Chemical mixing of
tracer turbulence diffusion was also simulated and compared with actual experimental results. The
TI&D arrangement showed an improvement of the fluid flow characteristics, yielding better tracer
distribution among the outlets, lower values of back mixing flow, and higher values of plug flow. A
mass transfer model coupled with k-« turbulence model predicted acceptably well the experimental
chemical mixing of the tracer in the water model. The water modeling and the numerical simulation
indicated that the TI&D arrangement retains the tracer inside the vessel for longer times, increasing
the minimum residence time. These results encourage the use of turbulence-inhibiting devices in
bloom and billet casters, which pursue excellence in product quality.
I. INTRODUCTION TI on the fluid flow pattern, tracer diffusion, and tracer
distribution in the different strands of a four-strand tundishMELT flow control in tundishes with one or two strands
of a bloom caster. Other important aspects considered were
using dams, weirs, and baffles has been widely studied using
the melt flow performance comparisons, among the bare
water models.[1\u20138] Melt flow in multiple-strand tundishes
tundish, MFCD consisting of dams and a waved impact pad,for billet and bloom casters has been studied using water
and the TI itself. In order to obtain these objectives, water
modeling and mathematical simulation techniques.[9\u201314]
and mathematical modeling techniques were applied simul-More recently, these techniques also have been employed
taneously, reaching useful conclusions in a complemen-to develop turbulence inhibitors. These devices are essential
tary fashion.to decrease fluid turbulence in the pouring region in one-
and two-strand tundishes.[15\u201320]
Turbulence inhibitors have been shown to be very useful II. WATER MODELING
to avoid slag entrapment, pick up of oxygen and nitrogen
A 1/3-scale model, using the Froude criterion, was con-from the surrounding air during ladle changes, and decrease
structed using transparent Perspex (Bodega de Pla´sticos,downgraded steel during grade changes. It is a usual trend
Mexico) plastic sheets with a thickness of 0.0127 m. Figurethat, similar to other melt flow control devices (MFCD), a
1 shows the geometric dimensions of this model. As can beturbulence inhibitor (TI) should be designed and manufac-
seen, the positions of the outlets are nonsymmetrical withtured on a tailor-made basis. Every TI should be designed
respect to the central axis of both sides of the tundish. Threeaccording to the tundish size, melt depth, flow rate, and
types of tundishes were studied: the bare tundish (BT), atundish design.
tundish with MFCD consisting of two pairs of baffles andIn the present work, melt flow control using a turbulence
a waved impact pad (BWIP), and a tundish with MFCDinhibitor in a four-strand tundish of a bloom caster is thor-
consisting of a TI and a pair of dams (TI&D).oughly studied. In this sense, this is the first report dealing
Design of the high baffles for the BWIP arrangement iswith the employment of a TI in a multiple-strand tundish.
shown in Figure 2(a). Figure 2(b) shows the design for theA multiple-strand tundish presents various challenges such
low dams, while Figure 2(c) shows a scheme of the wavedas being able to maintain the same casting temperature,
impact pad. Similarly, the TI&D arrangement is shown inhomogeneous chemistry, and similar steel cleanliness in
Figures 3(a) and (b). The first one shows the dam designevery strand.
and the second one the TI.The objective in this work was to study the effects of a
The positions of the two pairs of dams inside the tundish
for the BWIP arrangement and those corresponding to the
TI&D arrangement are indicated in Figure 4. Stopper rods
R.D. MORALES, Professor, and J. PALAFOX-RAMOS, Postdoctoral perform flow rate control of fluid, one for each outlet. TheStudent, are with the Department of Metallurgy and Materials Engineering,
operating conditions of the tundish are reported in Table I.Institute Polytechnic National, ESIQIE, C.P. 07300, Mexico. J. de J.
In order to determine the Residence Time DistributionBARRETO, Professor, is with the Materials Graduate Center, Institute
Tecnologico de Morelia, C.P. 58120-Morelia, Mexico. S. LOPEZ-RAMIREZ, (RTD) curves, tracer experiments were carried out using a
formerly Postdoctoral Student, Department of Metallurgy and Materials red dye that was injected in the inlet stream at a time zero.
Engineering, Institute Polytechnic National, ESIQIE, is Researcher, The tracer concentration was measured in two of the outlets,FOSECO INC., 20200 Sheldon Road, Cleveland, OH 44142.
one called the interior (the nearest one to the inlet) and theD. ZACHARIAS, Research Engineer, is with FOSECO INC.
Manuscript submitted October 18, 1999. other one exterior (the nearest one to the end wall of the
METALLURGICAL AND MATERIALS TRANSACTIONS B VOLUME 31B, DECEMBER 2000\u20141505
(a)
Fig. 1\u2014Geometric dimensions of the water model (m).
(b)
tundish), using two UV spectrophotometers. The output sig-
nals from these apparatuses were fed to a PC equipped with
a data acquisition card provided with software to process
the raw data into dimensionless variables according to well-
known proce-dures.[21]
Thus, assuming that the volumetric flow rates through
the four strands are identical, the amount of injected tracer
flowing out in a period dt through the i strand will be[22].
dmi 5 Ci (t)Qdt [1]
where Ci is the tracer concentration in the outlet i, Q the
volumetric flow rate, and mi the tracer mass at the strand i
(List of Symbols).
Allowing M to be the total mass of the pulse tracer (c)
injected, we obtain, by definition, the following expression:
Fig. 2\u2014Geometric dimensions for the BWIP tundish arrangement (m): (a)
tall baffles, (b) short baffles, (c) waved impact pad.dmi
M
5 Ei (t)dt [2]
model was designed to simulate the fluid flow of waterIntegrating this equation for all strands,
inside the tundish model as well as the chemical mixing
process of the tracer injected by a pulse in the incominge`0 E1 (t)dt 1 e
`
0
E2 (t)dt 1 . . . . 5 1 [3]
stream. It involves the solution of the three-dimensional (3-
or simply D) Navier\u2013Stokes equations of turbulence, the mass transfer
equation, continuity equation, and two equations for the k-«e`0 E (t)dt 5 1 [4] model chosen to represent turbulent viscosity. The equations
were reduced to their finite-difference equivalents by integ-
Once the RTD curve given by Eq. [4] was determined, the rating over the computational cells into which the 3-D
flow parameters were calculated using the methods dis- domain was divided, as shown in Figure 5. Turbulent
cussed in Reference 21. momentum equations were solved to yield steady-state con-
ditions and the turbulent mass transfer equation was solved
under unsteady-state conditions. This is a similar procedureIII. MATHEMATICAL MODELING
to that employed in the physical model, i.e., the fluid is
A. Fundamental Equations allowed to stabilize at a constant volumetric flow rate and
at an arbitrary tune taken as zero, the tracer is injectedTwo cases were considered in this study, the bare tundish
and the tundish with a TI&D arrangement. A mathematical starting its unsteady chemical mixing in the fluid.
1506\u2014VOLUME 31B, DECEMBER 2000 METALLURGICAL AND MATERIALS TRANSACTIONS B
Fig. 5\u20143-D computational mesh employed in the mathematical model.
Continuity equation:
(a) ­r
­t
1
­
­xj
(ruj) 5 0 [5]