11 pág.


Disciplina:Lingotamento Contínuo de Aços29 materiais61 seguidores
Pré-visualização5 páginas
as can be seen in Figure 6(b).


(a) (b)

(c) (d)
Fig. 10—Velocity fields of water in the tundish model: (a) entry plane in the BT arrangement, (b) plane located between both outlets in the BT arrangement,
(c) entry plane in the TI&D arrangement, and (d ) plane located between both outlets in TI&D arrangements.

Although there is still some difference between the minimum distribution in both outlets. This step is expected to influence
the fluid flow by driving it toward the upper surface of theresidence times for both outlets, this difference is smaller

than in the precedent case. The minimum residence time for bath, as is schematically shown in Figure 7. It is envisaged
that in this step flow, the fluid, flowing downstream, firstthe interior outlet prevails smaller than the exterior one.

Both curves show apparent similar statistical dispersion and hits the upper edge of the dam and changes its direction
upward, suffering a further impulse when it hits the step.the curve for the exterior outlet reports an irregular shape

after the concentration peak. This phenomenon was consis- This allows the tracer to follow a longer path, increasing its
residence time inside the tundish.tently observed in all the experimental trials. Furthermore,

it was observed that its origin lies in the fact that the holes Figures 8(a) and (b) show the RTD curves for the interior
and exterior outlets when the positions of the dams arein the multiple-hole baffles promoted the downstream pas-

sage of the tracer by packages. An intense bath surface 0.23 and 0.24 m (one position before and another after the
optimum position whose results are reported in Figure 6(c))turbulence in the pouring box zone was observed.

With the TI&D arrangement (Figure 6(c)), the fluid flow from the entry nozzle, respectively. As seen, in contrast to
the RTD curves when the dams are located 0.235 m fromis markedly improved. The minimum residence times in both

outlets are practically equal and so are the peak concentration the entry nozzle (Figure 6(c)), these new positions change
appreciably the tracer distribution in both nozzles. However,values. These latter values are also higher than the respective

concentration peaks for the BWIP arrangement. Besides it should be said that the flow characteristics for the outlets
in both cases remain superior to those corresponding to thethese improvements, the TI&D arrangement has the advan-

tage over the BWIP that it employs only three pieces in the bare tundish and the tundish with the BWIP arrangement
(compare Figures 6(a) and (b) with Figures 8(a) and (b)).tundish furniture instead of five. The bath surface turbulence

in the pouring box decreased considerably in comparison Table II shows a summary of the flow quantification
parameters for the BT and the tundish with the BWIP andwith the two previous cases.

The special design of the dams in the TI&D arrangement, TI&D arrangements; these values were calculated from the
experimental total RTD curves in Figure 9, using Eq. [3]using a step in their upper side, and their position inside

the tundish play a determinant role to control the tracer and following the procedure of Sahai and Emi.[21] It can be


(a) (b)

(c) (d)
Fig. 11—Velocity fields of water in the tundish model: (a) interior outlet in BT arrangement, (b) exterior outlet in BT arrangement, (c) interior outlet in
TI&D arrangement, and (d ) exterior outlet in TI&D arrangement.

seen that the TI&D arrangement reduces the dead volume same two planes, respectively, in the tundish with the TI&
D arrangement. At the entry plane of the bare tundish, thefraction, in contrast to the arrangement BWIP. It also

increases the plug flow volume fraction, reducing the mixed fluid observes a recirculating flow with highest velocities,
directed to the upper bath surface, near the wall after strikingvolume fraction. Using these traditional MFCDs promotes

the formation of undesirable zones. Another important flow the tundish floor (Figure 10(a)). In the same plane, the TI
controls the fluid turbulence and the recirculating flowcharacteristic of the TI&D arrangement is that it exhibits

lower fluid dispersion, represented by the dispersion parame- remains, but with smaller velocity vectors directed toward
the tundish floor located near the walls (Figure 10(c)). Inter (D/UL). These results support the contention that the

traditional MFCD are not as effective in controlling the the plane between the outlets, the recirculating pattern
remains as an influence of the high turbulence promoted byflow as the turbulence-inhibiting device. In addition to the

metallurgical and operational advantages of using turbulence the entry liquid jet (Figure 10(b)). The corresponding flow
pattern using the TI&D arrangement shown in Figure 10(d)inhibitors, their employment in multistrand tundishes can

help to obtain homogeneous steel chemistries. Implicit with indicates that the recirculating flow is eliminated, indicating
that transverse mixing is decreased.this there is also the possibility to obtain equal temperatures

and steel cleanliness in all strands of tundishes belonging Water flow characteristics in the planes of both outlets
(interior and exterior) are shown in Figures 11(a) throughto billet and bloom casters, opening a much wider application

of this device. Mainly, billet casters pursuing excellence in (d). Figure 11(a) shows a strong recirculating nonsymmetric
flow, due to the position of the outlets, as indicated by theproduct quality will find this an important tool for flow,

temperature, chemistry, and cleanliness controls. stopper rods, in the plane of the interior outlet of the BT.
Essentially, the same features mentioned previously for the
entry plane are also observed here. The highest fluid veloci-B. Mathematical Modeling of Fluid Flow ties are directed toward the upper bath surface near the
tundish walls. In the exterior outlet, the same flow patternFigures 10(a) and (b) show the velocity field of water in

the entry plane and at a plane located between both outlets is formed, although velocity vectors are smaller because the
fluid loses momentum further the bare tundish, while Figures 10(c) and (d) show the






Fig. 13—Front view of the velocity field of water in the tundish model:
(a) outlet plane in BT arrangement, (b) outlet plane in TI&D arrangement,(d) (c) near wall plane in TI&D arrangement, and (d ) near wall plane in TI&
D arrangement.Fig. 12—Upper views of the velocity fields of water in the tundish model:

(a) upper bath surface in BT arrangement, (b) upper bath surface in TI&
D arrangement, (c) center plane of the bath height in BT arrangement, and
(d ) center plane of the bath height in TI&D arrangement.

D arrangement. Figures 13(c) and (d) show the same type
of information for planes located near the wall.

Figures 11 through 13 indicate clearly the three-dimen-For a TI&D arrangement, the velocity vectors do not
sional nature of this flow. The flow is nonsymmetric alsopresent recirculating flow characteristics as can be seen for
in the horizontal planes because of the nonsymmetric posi-the interior and exterior outlets in Figures 11(c) and (d),
tion of the outlets. In the BT, the liquid jet entrains waterrespectively. Flow patterns are very similar in both outlets.
in the pour box area (Figure 13(a)). In the tundish with theFrom Figures 10 and 11, the higher dispersion observed in
TI&D arrangement, there is the formation of a recirculatingFigure 6(a) for the BT, in comparison to the TI&D arrange-
flow, but the velocity vectors are small due to the influencement (Figure 6(c)) and reported in Table II, can be clearly
of the inhibitor (Figure 13(b)). Near the wall, the fluidexplained as follows. In the BT, the fluid keeps a