Contact:
Prof. Dr.-Ing. Egbert Baake
Institute for Electrothermal Processes
University of Hannover
Wilhelm-Busch-Str. 4
D-30167 Hannover
Germany
1
Tel.: +49 511 762 3248
Fax: +49 511 762 3275
e-mail: baake@ewh.uni-hannover.de
Internet: www.etp.uni-hannover.de
Institute for Electrothermal Processes
University of Hannover
Egbert Baake, Andrejs Umbrashko
Experimental investigations and
numerical modelling of metal melt flows
in induction furnaces
Sino-German-Workshop
October 11-12, 2004, Shanghai (China)
Conclusions
- experimental work
- 3D tansient numerical simulation
Melt flow in cold crucible furnace
- low frequency oscillations
- 3D flow structure
Introduction
Characteristics of turbulent metal
melt flow in induction furnaces
Contents
2
and mass exchange in
the melt
¬ Optimisation of the heat
y Intensive stirring for cleaning of
the melt (zinc removing)
y Avoiding of erosion and clogging
of the ceramic lining
y Avoiding of melt instabilities,
splashing or pinching
y Intensive stirring at the melt
surface (melting of small-sized
scrap, carburization process)
y Homogenisation of the
temperature, avoiding of
local overheating , but realizing of
sufficient superheating of the
entire melt
y Mixing and homogenisation
of the entire melt
Industrial process requirements for melting
in induction furnaces
3
Optimal design and optimisation of the operation
behaviour of induction furnaces needs 3D instationary
numerical simulation of the turbulent melt flow and the
heat and mass transfer using experimentally verified
models
4
Experimental investigations, e.g. measurements of the
turbulent melt flows are very limited in industrial furnaces,
experimental investigations are possible in model furnaces
with model melts
Heat and mass transfer and the temperature distribution in
the melt are determined by 3D instationary turbulent melt
flows
Main features of the induction furnace metal
melting processes
liquid-solid-interface
skull
- superheating
- heat flow
- crucible temperature
temperature field
geometry of melt
meniscus shape
5
optimization of design and operating parameters
homogenisation of
melt
velocity field
- distribution of power
- el. efficiency
magnetic field
Physical Correlations
Baake, E. et.al.: 1994
Crucible bottom
Vmax ≈ 20 cm/s
Crucible wall
v′max
≈1
vmax
6
Melt flow measurements in induction crucible furnace
15
20
25
-25
-20
-15
-10
-5
0
5
10
Geschwindigkeit in cm/s
0
20
30
Zeit in s
40
¬ Low-frequency oscillations
¬ Oscillation period: 8...12 sec
10
50
7
Measurement of local flow velocity (ICF):
near the crucible wall between the main flow eddies
crucible bottom
crucible wall
Calculation results of turbulent
characteristics are different from
measurement results
8
Application of 2D and 3D RANS
(k-ε) turbulence models:
•Simulations
•Simulationsof
ofindustrial
industrialinstallations
installations
are
impossible
are impossible
••Steady-state
Steady-statesimulations
simulations
••Transient
Transient3D
3Dsimulations
simulations
••Relatively
Relativelyhigh
highmesh
meshresolution
resolutionrequirements
requirements
LES
LES
••Large
Largescales
scalesare
areresolved
resolveddirectly
directlywhile
whileonly
onlysmall
small
scales
scalesare
aremodelled
modelled
4
Re
Re≥≥10
104
9
••Very
Veryhigh
highrequirements
requirementsfor
for
computational
resources
computational resources
••Relatively
Relativelylow
lowmesh
meshresolution
resolution
requirements
requirements
CFD
CFDproblem
problem
DNS
DNS
••All
Allscales
scalesare
areresolved
resolveddirectly
directly
RANS
RANS(k-ε
(k-εmodel)
model)
••Whole
Wholeenergy
energyspectrum
spectrumisismodelled
modelled
0
0,05
0,1
0,15
0,2
0,25
-0,25
-0,2
-0,15
-0,1
-0,05
Geschwindigkeit in m/s
0
10
Zeit in s
30
40
50
60
¬ Low-frequency oscillations
¬ Oscillation period: appr. 10 sec
20
r = 0.075
r = 0.14
r = 0.155
Calculated local flow velocity:
(3D transient LES)
10
Amplitude
Measurement
Frequency (Hz)
Calculation
Fourier analysis of the measured and calculated
oscillations of the axial velocity components near
the crucible wall between the main flow eddies
11
velocity magnitude
azimuthal velocity
12
particles trajectories
Long-time period averaged velocity field
in the melt of the ICF (3D transient LES)
Filling level 90 %
Rcr = 0.49 m
Hind = 1.33 m
P = 4540 KW
3D hydrodynamic model of an industrial
induction crucible furnace
13
Experiment
(model furnace)
Calculations
(industrial furnace)
Kinetic energy of the oscillations
14
Time-averaged flow pattern [m/s]
15
Transient flow development [m/s]
16
Transient flow development (cross-section) [m/s]
17
Calculation of the particle tracing in the melt
of the ICF (3D transient LES)
18
(water cooled)
bottom
melt with
meniscus
shape
current
(water cooled
inductor
(water cooled)
crucible
segment
slit
melt flow
radiation
heat conduction
skull
EM-forces
19
heat losses by radiation
and conduction depending
on the meniscus shape
water cooled bottom and
crucible segments leads to
solid layer (skull)
free melt surface, based
on electromagnetic forces
slitted crucible to realize
efficient electromagnetic
transparency
Features of the Induction Furnace with Cold Crucible
crucible-bottom
bottom-skull
wall-skull
contact point
ideal
free surface
real
inductor
crucible
Reliable, reproducible and stable
melting process
20
Improvement of the total efficiency of
process
Maximisation of the overheating
temperature, which is the key
parameter of the process
Optimisation of electromagnetic and
thermal parameters
Cold crucible induction furnace
TT==660-720°C
660-720°C
PP==200
200kW
kW
ff==9.2
9.2kHz
kHz
55coil
coilturns
turns
i
RRc ==72.5
72.5mm
mm
c
HHi ==208
208mm
mm
Experimental set-up for semi-levitation melting
21
Melting process of Aluminium
22
Temperature measurements in Aluminium
23
Measured temperature field in Aluminium
24
electrodes
magnet core
coil
35
stainlesssteel case
stainlesssteel holder
6 14
Melt flow measurements in Aluminium with the
electromagnetic velocity probe
25
Flow pattern and temperature distribution simulated
with 2D RNG k-ε turbulence model
26
*HLRN – scientific supercomputer
network of North Germany
27
Parallel
Parallel computations
computations with
with
FLUENT
FLUENT 6.1
6.1 software
software at
at
the
the HLRN*-system
HLRN*-system
Smagorinsky-Lilly
Smagorinsky-Lilly subgrid
subgrid
viscosity
viscosity model
model
Time
Time step
step 10
10 ms
ms
6
~3.8•10
~3.8•106 elements
elements
3D LES-model for Aluminium melting
vm~40 cm/s
Time-averaged
Time-averagedflow
flowpattern
pattern
[m/s]
28
An
Anintermediate
intermediateflow
flowpattern
pattern
[m/s]
Results of 3D transient LES modeling
Results of 3D transient LES modeling
29
Time-averaged
Time-averagedtemperature
temperature
distribution
distribution
ºC
Measured
Measuredtemperature
temperature
distribution
distribution
ºC
Results of 3D transient LES modelling
30
Results of 3D transient LES modelling
31
Results of 3D transient LES modelling
32
33
3D-transient LES is a reliable numerical tool to simulate the
turbulent melt flow with in-stationary low-frequency flow
oscillations in induction melting installations
Comparison of the LES modelling results with experimental
results show good agreement
Heat and mass transfer processes in the melt of induction
furnaces are significantly influenced by large scale
low-frequency oscillations of the recirculating flow
main eddies
Conclusions