Jiang_et_al_2010
6 pág.

Jiang_et_al_2010


DisciplinaLingotamento Contínuo de Aços30 materiais62 seguidores
Pré-visualização3 páginas
the gas hole is 
2.0 mm. Fig. 4 shows the shape and the size of the porous 
plug. 
 
J. Jiang et al., Water modeling of molten steel flow in a multi-strand tundish with gas blowing 145 
 
 
 
 
 
 
Fig. 3. Cases investigated in this study: (a) case 2, 180 L/h, 210 mm×56 mm; (b) case 3, 90 L/h, 210 mm×56 mm; (c) case 4, 90 L/h, 
210 mm×56 mm; (d) case 5, 90 L/h, 105 mm×56 mm; (e) case 6, 60 L/h, 105 mm×56 mm; (f) case 7, 120 L/h, 210 mm×56 mm; (g) 
case 8, 120 L/h, 105 mm×56 mm; (h) case 9, 120 L/h, 105 mm×56 mm; (i) case 10, 120 L/h, 210 mm×28 mm; (j) case 11, 120 L/h, 210 
mm×56 mm. 
 
Fig. 4. Porous plug used in the water experiments. 
3. Results and discussion 
Fluid flow characteristics in the water model are listed in 
Table 2. The dead flow volume fraction in most tundishes 
with gas blowing is less than that in the prototype tundish, 
but case 2 is an exception, and the reason will be discussed 
later. Therefore, proper gas blowing can reduce the dead 
flow volume fraction in the tundish. However, it is noticed 
that the minimum residence time in case 1 is the longest, so 
gas blowing reduces the minimum residence time in the 
current tundish. This is different from the results obtained by 
Zhong et al. [2], whose results showed that gas blowing 
hardly influenced the minimum residence time. Perhaps this 
is due to the different tundish configurations used in the two 
investigations. 
146 Int. J. Miner. Metall. Mater., Vol.17, No.2, Apr 2010 
 
Table 2. Fluid flow characteristics in the water model 
Case tmin / s tmax / s tav / s Vdv / %
Case 1 62 275 665 11.0 
Case 2 42 412 658 12.0 
Case 3 38 305 679 9.1 
Case 4 54 351 685 8.3 
Case 5 42 448 713 4.8 
Case 6 52 446 710 5.0 
Case 7 41 422 726 2.9 
Case 8 61 402 709 5.2 
Case 9 58 360 684 8.5 
Case 10 59 373 677 9.4 
Case 11 36 377 681 8.9 
 
In cases 2 and 11, the minimum residence times are very 
short, 42 and 36 s, respectively. When the flow jets reached 
the bottom of the turbulence inhibitor, first, flew up and then 
flew into the 3 holes in the baffle. The flow coming from the 
front hole was divided into 2 parts, one part flew into the 
surface of the molten steel due to the driven force from bub-
bles, and the other part flew into the middle outlets directly. 
Therefore, the minimum residence time in the middle outlets 
was much shorter than that in the side outlets because of the 
front hole in the baffle, which caused the flow in the tundish 
inhomogeneous. Therefore, the middle hole (shown in Fig. 1) 
on the baffle was covered in the following experiments. 
For cases 3 and 4, the gas flow rate is same, but the gas 
blowing location is different. According to the results in Ta-
ble 2, the dead flow volume fraction in case 4 is 8.3%, 
smaller than that in case 3. Cases 3 and 5 have the same gas 
blowing location and gas flow rate but different areas of 
porous plug; however, the dead flow volume fraction in case 
5 is smaller than that in case 3. For case 6, the gas flow rate 
is smaller than that in case 5, but case 6 gets a longer mini-
mum residence time. Therefore, the gas blowing location, 
gas flow rate, and the area of porous plug gas greatly influ-
ence the flow characteristics in a tundish, the gas blowing 
location near the baffle, smaller gas flow rate, and smaller 
area of porous plug are better for improving fluid flow 
characteristics. This conclusion also can be proved in the 
following experiments. 
For cases 7 and 8, the gas flow rate and area of porous 
plug are same, but the gas blowing location is different. The 
minimum residence time is only 41 s for case 7, but for case 
8, the minimum residence time reaches 61 s. In case 7, all 
the flow from the side holes in the baffle flows into the sur-
face along the bubbling curtain and then flows down quickly 
due to the absorbing force on the outlet, and reaches the 
middle outlets first. In case 8, the porous plug is far from the 
side holes, so part of the flow from the side holes can keep 
the same flow direction, and the other part will flow into the 
surface of the fluid along the bubbling curtain. The velocity 
of the second flow becomes slow because the first flow 
weakens the absorbing force at the outlet, so the minimum 
residence time in case 8 is longer than that in case 7. For the 
same reason, case 9 also achieved good experimental results; 
the minimum residence time is 58 s and the dead flow vol-
ume fraction is 8.5% 
Typical RTD curves for case 1 (without gas blowing) and 
case 10 (with gas blowing), are shown in Figs. 5 and 6, re-
spectively. It can be seen that the RTD curves in the tundish 
with gas bubbling curtain is obviously different from those 
without gas blowing. The peak concentration time of the 
tracer for the experiment with gas injection is significantly 
larger than that without gas blowing. The curves for the ex-
periment without gas blowing fluctuate in the vicinity of the 
peak concentration, while the curves for the case with gas 
 
Fig. 5. RTD curves for case 1 (without gas blowing): (a) global RTD curve; (b) local RTD curve. 
J. Jiang et al., Water modeling of molten steel flow in a multi-strand tundish with gas blowing 147 
 
 
Fig. 6. RTD curves for case 10 (with gas blowing): (a) global RTD curve; (b) local RTD curve. 
blowing reveal a smooth curve. This shows that the flow 
characteristics in the tundish can be improved by using gas 
blowing. It also can be noticed that both RTD curves for the 
outside outlet and inside outlet fit better in Fig. 6 than those 
in Fig. 5. For case 1, the minimum residence time at the 
middle outlet and side outlet is 52 s and 81s, respectively, 
but for case10, the minimum residence time at the middle 
outlet and side outlet is 59 s. Therefore, using gas blowing 
can reduce the difference of flows at the middle outlet and 
side outlet. 
Visual observation in the experiments with potassium 
permanganate solution as a dye tracer showed that the tracer 
decelerated before passing through the bubbling curtain and 
accelerated after flowing through the curtain. When it 
reached the bubbling curtain, the dye tracer changed the 
flow direction and reached the surface of fluid. Inclusions 
could be brought into the surface by the flow; and they were 
absorbed by top slag. The bubble produced by gas blowing 
could absorb small inclusion and also could provide the 
condition for inclusions collision and aggregation, which are 
good for inclusion removal. 
4. Conclusions 
(1) Gas blowing can greatly improve the flow character-
istics in the tundish with a turbulence inhibitor. It dramati-
cally increases the peak concentration time, greatly de-
creases the dead volume, and reduces the minimum resi-
dence time. 
(2) The gas blowing location, gas flow rate, and the area 
of porous plug area greatly influence the flow characteristics 
in the tundish; the gas blowing location near the baffle, 
smaller gas flow rate, and smaller porous plug area are bet-
ter. 
(3) Using gas blowing can reduce the difference of the 
flow at the middle outlets and side outlets for the 
multi-strand tundish. 
(4) Introducing gas blowing into a tundish and combining 
the turbulence inhibitor can improve inclusion floating and 
removal, and the cleanness of molten steel can be advanced. 
References 
[1] L. Zhang and S. Taniguchi, Fundamentals of inclusion re-
moval from liquid steel by bubble flotation, Int. Mater. Rev., 
45(2000), No.2, p.59. 
[2] L.C. Zhong, L.Y. Li, B. Wang, M.F. Jiang, L.X. Zhu, L. 
Zhang, and R.R. Chen, Water modelling experiment of argon 
bubbling curtain in a slab continuous casting, Steel Res. Int., 
77(2006), No.2, p.103. 
[3] M.J. Zhang, H.Z. Wang, A. Huang, Q.X. Meng, and H.Z. Gu, 
Water modeling of effect on steel liquid flow in the bottom 
gas blowing tundish of different porous materials, J. Wuhan 
Univ. Sci. Technol. Nat. Sci. (in Chinese), 29(2006), No.5, 
p.433. 
[4] M.J. Zhang, H.Z. Wang, A. Huang, H.Z. Gu, and D.Q. Liu,