validation of fluid flow and solidification simulation of a continuous...

University of Illinois at Urbana-Champaign • Metals Processing Simulation Lab • Brian G. Thomas

Validation of Fluid Flow and Solidification Simulation of a Continuous Thin-Slab Caster

Validation of Fluid Flow and Solidification Simulation of a Continuous Thin-Slab Caster

Brian G. Thomas1, Ron O'Malley2, Tiebiao Shi1, Ya Meng1, David Creech1, and David Stone1

1 University of Illinois at Urbana-Champaign,

Department of Mechanical and Industrial Engineering,1206 West Green Street, Urbana, IL USA, 61801

2 AK Steel Research

703 Curtis StreetMiddletown, Ohio 45043

Brian G. Thomas1, Ron O'Malley2, Tiebiao Shi1, Ya Meng1, David Creech1, and David Stone1

1 University of Illinois at Urbana-Champaign,

Department of Mechanical and Industrial Engineering,1206 West Green Street, Urbana, IL USA, 61801

2 AK Steel Research

703 Curtis StreetMiddletown, Ohio 45043


AcknowledgementsAcknowledgements

l Continuous Casting Consortium AK Steel, Allegheny Ludlum Corp., Columbus Steel, Ispat-Inland Steel, LTV Steel, Stollberg Inc.

l National Science Foundation (Grant DMI-98-00274)

l NCSA (computing time and use of CFX)

l AK Steel (water model and plant measurements)

l M. Langeneckert and G. Webster (finite element analysis of the mold)

l Continuous Casting Consortium AK Steel, Allegheny Ludlum Corp., Columbus Steel, Ispat-Inland Steel, LTV Steel, Stollberg Inc.

l National Science Foundation (Grant DMI-98-00274)

l NCSA (computing time and use of CFX)

l AK Steel (water model and plant measurements)

l M. Langeneckert and G. Webster (finite element analysis of the mold)


ObjectiveObjective

Validate fluid flow and solidification models with extensive measurements:Validate fluid flow and solidification models with extensive measurements:

l velocities within the liquid pool (from water models)

l temperatures measured in the molten steel pool (plant trial)

l temperatures measured in the copper mold walls (mold thermocouples)

l heat flow rate (heat balance on the mold cooling water)

l thickness of the solidified steel shell (from breakout shell measurements)

l velocities within the liquid pool (from water models)

l temperatures measured in the molten steel pool (plant trial)

l temperatures measured in the copper mold walls (mold thermocouples)

l heat flow rate (heat balance on the mold cooling water)

l thickness of the solidified steel shell (from breakout shell measurements)


The Continuous Casting Process

B.G. Thomas


Thin Slab Casting MoldThin Slab Casting Mold


Fluid Flow ModelFluid Flow Model

3D Domain and Mesh of¼ of Liquid Pool:

l Includes 3-port nozzle

l Standard high-Re K-ε turbulence model and wall laws

l Solidification front (boundary): liquidus temperature

l Predicts velocities and superheat distribution

3D Domain and Mesh of¼ of Liquid Pool:

l Includes 3-port nozzle

l Standard high-Re K-ε turbulence model and wall laws

l Solidification front (boundary): liquidus temperature

l Predicts velocities and superheat distribution


3-D K-ε Simulation Water Model3-D K-ε Simulation Water Model


Water Model FlowWater Model Flow

Velocity Along Flowing Jet (Calculated and Water Model Measurements)

Velocity Along Flowing Jet (Calculated and Water Model Measurements)

0

0.2

0.4

0.6

0.8

1

100 150 200 250 300 350 400 450 500

Calculated Speed (Jet Centerline)Calculated Speed (Average)Measured Speed

Vel

ocity

(m

/s)

Horizontal Distance from Mold Center (mm)


Molten Steel Temperature(Model Validation)

Molten Steel Temperature(Model Validation)

Pour

Liquidus 56°C superheat

0

10

20

30

40

50

0 50 100 150 200

Probe (insertion)

Probe (withdrawal)

Model

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

Sup

erhe

at (

C)

Distance below the Meniscus (mm)

SEN

Profile Location

Measurement Position

NFMiddle Point


Superheat Flux Profiles(Calculated Around the Exterior of the Strand Surface)

Superheat Flux Profiles(Calculated Around the Exterior of the Strand Surface)

0

0.5

1

1.5

2

2.5

30 1000 2000 3000 4000

Corner

Wideface centerline

Narrow face centerline

Dis

tanc

e be

low

Men

iscu

s (m

)

SuperHeat Flux from liquid to shell (KW/m2)


Temperature Contours in 3-D Portion of Mold WallTemperature Contours in 3-D Portion of Mold Wall

Wide FaceWide Face


Instrumented Mold (106 Thermocouples)Instrumented Mold (106 Thermocouples)

Dist (mm)Dist (mm)


Heat Flux and Cooling Water Heat BalanceHeat Flux and Cooling Water Heat Balance

0

0.5

1

1.5

2

2.5

3

3.5

4

0 200 400 600 800 1000 1200

Wide Face

Narrow Face

Hea

t Flu

x (M

Wm

-2)

Distance below Meniscus (mm)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 200 400 600 800 1000 1200

Wide Face

Narrow Face

Hea

t Flu

x (M

Wm

-2)


Breakout shell

Steady state

8.228.287.98Narrow Face

5.616.286.12Wide Face

CON1D predicted

measurementsUnit : oC


Temperatures Down Mold Walls (Calculated and Measured at Thermocouple Locations)

Temperatures Down Mold Walls (Calculated and Measured at Thermocouple Locations)

70

80

90

100

110

120

130

140

0 200 400 600 800 1000

IR WF 325 mm East of CLIR WF 75 mm East of CLIR WF 75 mm west of CLIR WF 325 mm west of CLOR WF 325 mm East of CLOR WF 75 mm East of CLOR WF 75 mm west of CLOR WF 325 mm west of CLCON1D predicted WF

Tem

pera

ture

(C

)

Distance from Top of Mold (mm)

70

80

90

100

110

120

130

140

0 200 400 600 800 1000

IR WF 325 mm East of CLIR WF 75 mm East of CLIR WF 75 mm west of CLIR WF 325 mm west of CLOR WF 325 mm East of CLOR WF 75 mm East of CLOR WF 75 mm west of CLOR WF 325 mm west of CLCON1D predicted WF

Tem

pera

ture

(C

)


CON1D calculation offset: 4.5mm 10.3mmCON1D calculation offset: 4.5mm 10.3mm

80

100

120

140

160

180

0 200 400 600 800 1000

East NF center

West NF center

CON1D predicted NF

Tem

pera

ture

(C

)


Wide FaceWide Face Narrow FaceNarrow Face


Solidification and Heat Transfer Model: CON1DSolidification and Heat Transfer Model: CON1D

l 1-D transient finite-difference model of solidifying steel shell

l 2-D steady-state heat conduction within the mold wall

l detailed treatment of interfacial gap including mass and momentum balances on slag layers

l uses superheat flux from flow modell predicts:

-shell thickness down the mold-temperature in the mold and shell -slag layer thicknesses (solid & liquid) -heat flux down the mold-mold water temperature rise-ideal taper of mold walls

l 1-D transient finite-difference model of solidifying steel shell

l 2-D steady-state heat conduction within the mold wall

l detailed treatment of interfacial gap including mass and momentum balances on slag layers

l uses superheat flux from flow modell predicts:

-shell thickness down the mold-temperature in the mold and shell -slag layer thicknesses (solid & liquid) -heat flux down the mold-mold water temperature rise-ideal taper of mold walls

(MW/m )2 Heat fluxHeat flux

Peak near meniscus

Copper Mold and Gap

Liquid Steel

1.0123

Dis

tanc

e be

low

men

iscu

s (m

m)

400

200

top of mold

23 mm

4

0

Mold Exit

600

Heat Input to shell inside from liquid (q )

Water Spray Zone

Meniscus

Narrow face (Peak near mold exit)

(MW/m )2

Solidifying Steel Shell

1200 ÞC1300 ÞC

1400 ÞC1500 ÞC

1100 ÞC

800

Wide face (Very little superheat )

int sh

x

z

Heat Removed from shell surface to gap (q )


Solid Fraction Effect on Steady-state Shell ThicknessSolid Fraction Effect on Steady-state Shell Thickness

0

2

4

6

8

10

12

14

16

18

20

0 200 400 600 800 1000 1200

She

ll T

hick

ness

(m

m)

Distance below meniscus (mm)

fs=0fs=0.1fs=0.3fs=0.7fs=1.0


Section through slab showing longitudinal crack that started breakout

Section through slab showing longitudinal crack that started breakout

NarrowFace

NarrowFace

CenterlineCenterline


Casting Conditions & Simulation parametersCasting Conditions & Simulation parameters

l Casting Speed: 1.524m/minl Pour Temperature: 1563 oC (61 oC superheat)l Slab Size: 984mm*132mml Mold Length: 1200mml Nozzle Submerge depth: 127mml Mold Powder Consumption Rate: 0.48kg/m2

l Mold Thickness: wide face 35mm; narrow face 25mml Steel Grade: 434 Stainless Steell Inlet Cooling Water Temperature: 25 oCl Fraction Solid for Shell Thickness Location: 0.1

l Casting Speed: 1.524m/minl Pour Temperature: 1563 oC (61 oC superheat)l Slab Size: 984mm*132mml Mold Length: 1200mml Nozzle Submerge depth: 127mml Mold Powder Consumption Rate: 0.48kg/m2

l Mold Thickness: wide face 35mm; narrow face 25mml Steel Grade: 434 Stainless Steell Inlet Cooling Water Temperature: 25 oCl Fraction Solid for Shell Thickness Location: 0.1


Events during breakoutEvents during breakout

0

500

1000

1500

2000

7120 7140 7160 7180 7200 7220 7240 7260

Dis

tanc

e be

low

ste

ady-

stat

e m

enis

cus

(mm

)

Time (s)

t0

t0 - 10

t0 - 20

t0 - 30

t0 - 40

t0 - 50

t0 - 57

mold exit

Estimated liquid level

Bottom of breakout hole

Measured liquid levelTop of breakout shell

0

500

1000

1500

2000

7120 7140 7160 7180 7200 7220 7240 7260

Dis

tanc

e be

low

ste

ady-

stat

e m

enis

cus

(mm

)

Time (s)

t0

t0 - 10

t0 - 20

t0 - 30

t0 - 40

t0 - 50

t0 - 57

mold exit

Estimated liquid level

Bottom of breakout hole

Measured liquid levelTop of breakout shell


Shell Thickness Along Wide Face (WF)(Calculated Compared with Breakout Shell Measurements)


0

5

10

15

20

25

30

0 200 400 600 800 1000

IR WF 86mm East of CLIR WF 86mm West of CLOR WF 86mm East of CLOR WF 86mm West of CLCON1D Transient CON1D Steady-State

She

ll T

hick

ness

(mm

)


Solidifcation Time (s)0 10 20 30 40 50




0

5

10

15

20

25

30

0 200 400 600 800 1000

IR WF 86mm East of CLIR WF 86mm West of CLOR WF 86mm East of CLOR WF 86mm West of CLIR WF 238mm East ofCLIR WF 238mm West of CLOR WF 238mm East of CLOR WF 238mm West of CLCON1D Transient CON1D Steady-State

She

ll T

hick

ness

(mm

)




Shell Thickness Along Narrow Face (NF) (Calculated Compared with Breakout Shell Measurements)

Shell Thickness Along Narrow Face (NF) (Calculated Compared with Breakout Shell Measurements)

0

5

10

15

20

25

30

0 200 400 600 800 1000

East NF CenterWest NF CenterCON1D TransientCON1D Steady-State

She

ll T

hick

ness

(mm

)




Model ApplicationsModel Applications

These validated modeling tools can now be applied to study related phenomena of practical significance in a quantitative manner, which include:

l ideal taper of the mold walls to match the shell shrinkage,

l critical shell thickness to avoid breakouts,

l behavior of flux layers in the interfacial gap,

l crack formation,

l relationships between mold wall temperatures and events in solidifying shell to enable online quality prediction.

These validated modeling tools can now be applied to study related phenomena of practical significance in a quantitative manner, which include:

l ideal taper of the mold walls to match the shell shrinkage,

l critical shell thickness to avoid breakouts,

l behavior of flux layers in the interfacial gap,

l crack formation,

l relationships between mold wall temperatures and events in solidifying shell to enable online quality prediction.


ConclusionConclusion

l An efficient model of 3-D turbulent flow, heat transfer and solidification in a thin slab caster has been developed, featuring one-way coupling betweenä K-ε flow model (CFX) and ä 1-D transient model of heat transfer in the mold, interface, and

solidifying steel shell (CON1D).

l The accuracy of this modeling approach has been demonstrated by comparison with

ä experimental measurements of fluid flow in the liquid pool,ä temperature in the molten steel, ä temperature in the copper mold walls, ä temperature increase of the cooling water, and ä breakout shell thickness.

l An efficient model of 3-D turbulent flow, heat transfer and solidification in a thin slab caster has been developed, featuring one-way coupling betweenä K-ε flow model (CFX) and ä 1-D transient model of heat transfer in the mold, interface, and

solidifying steel shell (CON1D).

l The accuracy of this modeling approach has been demonstrated by comparison with

ä experimental measurements of fluid flow in the liquid pool,ä temperature in the molten steel, ä temperature in the copper mold walls, ä temperature increase of the cooling water, and ä breakout shell thickness.

validation of fluid flow and solidification simulation of a continuous...

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