Investigation on the Convection Pattern of Liquid Steel in the Continuous Casting Tundish by Theoretical Analysis, Water Model Experiment and CFD Simulation.

Investigation on the Convection Pattern of Liquid Steel in the Continuous Casting Tundish by Theoretical Analysis, Water Model Experiment and CFD Simulation

D. Y. Sheng Lage Jonsson

Process Metallurgy Department,MEFOS, S 97125, Lulea, Sweden

Tel: 0046-920-201934Fax: 0046-920-255832

Email: sheng@mefos.se

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Process Introduction

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Ladle with clean steel

40 ppm Otot

Slag

20-30 ppm

Stirring

Shroud Stopper (Ar-bubbling)

10-20 ppm

Nozzle

Mould Slag+casting powder

Slag+cover powder

Tundish

Blow-Holes

(Ar+Al 2O3)

BOF

EAFBF Function of Tundish:Tradition:1, Steel distribution vessel

Modern: 2, Inclusion removal3, Alloy trimming4, Superheat control5, Homogenisation

Tundish Metallurgy

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Problem Arisement Two different opinions:The steel flow in tundish is:1, Forced Convection System?OR2, Mixed Convection System?

Thermal conditions:

1, Heat loss 2, External heating and cooling3, Variation of inlet temperature

Objective

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CFD Causes to This Study !Two different flow pattern are on my screen

Is this true ?

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Theoretical Consideration

F

F

gl

u l

Grbouyancy

inertia

~( )* ( / )

( )* ( / )~Re

3 2

2 2 2 2

( / Re )( / )

( / ).Gr

gl T

ul

g T l

uTs

s

s

s s s

ss

23 2

2 2 474

( / Re )( / )

( / ).Gr

gl T

ul

g T l

uTw

w

w

w w w

ww

23 2

2 2 4 00

Dimensional Anaysis:

Tundish

Water Model

(1) Even one degree temperature difference in the tundish, buoyancy can not be ingored.(2) Water model can be used to simulate the convection pattern due to similar of this dimensionless number.

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Water Model Experiment

1

2

4

5

6 7

893

10

11

Interface

Microcomputer

ladle(1)

tundish(2)

thermocouple

camera

outlet(3)

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Experimental measurements

0 50 100 150 200 250 300 35010

15

20

25

30

35

Time, (s)

Te

mp

era

ture

, (¡æ

)

7

8

0 50 100 150 200 250 300 35010

15

20

25

30

35

Time, (s)

Te

mp

era

ture

, (¡æ

)

9

10

0 50 100 150 200 250 300 35010

15

20

25

30

35

Time, (s)

1

2

3

4

5

6

Te

mp

era

ture

, (¡æ

)

0 50 100 150 200 250 300 35010

15

20

25

30

35T

em

pe

ratu

re, (

¡æ)

dc

ba Time, (s)

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CFD Simulation

1. 3-D Navier-Stokes equations.

2. Standard k- two equations model

3. Free surface is kept at a fixed level.

4. Fluid flow and temperature are coupled

Modeling description

PHOENICS 3.1, Sun Enterprise 4000, 6 CPU 350 MHz

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Hotter Incoming (1)

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Cooler Incoming (1)

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Schematic of flow pattern

a, equal temperature inlet

b, hotter inlet

c, cooler inlet

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Verification (1)

0 30 60 90 120 150 180 210 240 270 300 330282

284

286

288

290

292

294

296

298

300

302

CFD model

Physical model

Tem

per

atu

re, (

K)

Time, (s)0 30 60 90 120 150 180 210 240 270 300 330

282

284

286

288

290

292

294

296

298

300

302

CFD model

Physical model

Tem

per

atu

re, (

K)

Time, (s)

0 30 60 90 120 150 180 210 240 270 300 330282

284

286

288

290

292

294

296

298

300

302

CFD model

Physical model

Tem

per

atu

re, (

K)

Time, (s)0 30 60 90 120 150 180 210 240 270 300 330

282

284

286

288

290

292

294

296

298

300

302

CFD model

Physical model

Tem

per

atu

re, (

K)

Time, (s)

No.6 No.10

No.9 No.4

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Verification (2)

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Hotter Incoming (2)

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Cooler Incoming (2)

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Future work

(1) Turbulence model of the transition region(2) Use the CFD model for real tundish simulation (3) Considersing the heat loss surrounding and additional heat source (4) Time dependent inlet temperature variation will be considered.

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Conclusion

(1) Dimensionless number Gr/Re 2 can be used to set up thermal similarity between water model and actual tundish(2) Thermal buoyancy driven flow is obvious in the non-isothermal water model (3) CFD simulation keeps good agreement with mesurement(4) The tundish is a mixed convection system