Anomalies of Joule heat,
thermal and turbulent flow fields
in clogged industrial channel induction furnaces
S.Pavlovs(1), A.Jakovics(1), D.Bosnyaks(1), B. Nacke(2), E. Baake(2)
(1)
Laboratory for Mathematical Modelling of Environmental and
Technological Processes,
Faculty of Physics and Mathematics, University of Latvia
(2)
Institute of Electrotechnology, Leibniz University of Hannover
HES-13 – International Conference
on Heating by Electromagnetic Sources
May 21-24, 2013
Padua, Italy
Existing problems
in Channel Induction Furnace (CIF)
Reduced operation life time of CIF channel
caused by erosion, infiltration and in particular
clogging (build up formations) of the ceramic lining
Build up in channel*
Constricted throat opening*
* Williams, D.C. and Naro R.L. (2007), “Mechanism and control of build up phenomenon in channel induction and
pressure pouring furnaces” (part 1), Ductile Iron News, Issue 1.
Existing problems in CIF
Clogging of the ceramic lining is influenced by:
 heat and mass exchange between channel and bath
 temperature distribution along the channel
 melt flow velocity distribution in the channel
 non-conductive sediments’ influence on ICF parameters
 impurities’ distribution in the melt
(especially oxides like MgO, Al2O3, etc.)
 and many others...
Schemes of build-up formation*
channel outlet
* (Williams D.C. et al., 2007)
throat
Computed models of industrial CIF
Clogged throat model –
CIF with sediments
in form of “hill”
Build-up channel model –
CIF with narrowed (25%)
left channel branch
Non-clogged model –
CIF original design
Geometry for modelling of EM field
Inductor current amplitude is fixed at 1850 A
Peculiarities of numerical computations
 EM field, Lorentz force and Joule heat:
• software package
• number of elements
ANSYS Classic 14.0
~ 1–1.5 million
 Structured mesh for HD and thermal fields:
• software package
• number of elements
ANSYS ICEM 14.0
~ 2.5–3.5 million
 Flow patterns and thermal field in the melt:
√ steady-state k-ω SST model –
for obtaining the initial conditions for transient
k-ω SST model
√ transient k-ω SST (Shear Stress Transport) model –
for preliminary analysis
for obtaining the initial conditions for LES computations
√ LES (Large Eddy Simulation) model of turbulence –
for detailed analysis
• software package
ANSYS CFX 14.0
Peculiarities of numerical computations
 Thermal boundary condition
Surface
Type of heat
transfer
Heat-transfer
coefficient
[W/(m2·K)]
Channel
Convection
33
–
330
Throat – side
Convection
30
–
330
Throat – bottom
Convection
37
–
330
Bath – top
Radiation
–
0.14
1650
Bath – side
Convection
3
–
330
Bath – bottom
Convection
7
–
330
Parameters under control:
√ Courant number
√ wall function
C << 1
y+ << 200–300
External
Emissivity temperature
[K]
Anomalies of velocity field:
build-up channel model –
near outlets to throat for left narrowed and right channel branches



v x e x  v y e y  v z ez


v x ex  v y e y
vz
Non-clogged model – CIF original design*
flow time t = 0–700 s
Temperature distribution in the channel for y=0: maximum Tmax and its position α
√ long-term oscillations’ periods for Tmax and α √ Tmax lags in phase in comparison with α
Tmax

√ overheating temperature   Tchannel  Tthroat
toscil
 toscil
~ 163 sec
√ time delay between extremes
Θ ~ 32 K
of Tmax position α and Tmax itself –
√ time-averaged transit velocity for x=0
aver
τ ~ 40 sec
vtrans
~ 2.8 cm/s
* Baake, E., Jakovics, A., Pavlovs,S., Kirpo M., (2010), “Long-term computations of turbulent flow and temperature field
in induction channel furnace with various channel design”, Magnetohydrodynamics, Vol. 46, No. 4, pp. 317-330.
Clogged throat model
Maximum of instantaneous temperature Tmax (K) and angle α (˚) of its position for y = 0
Averaged for cross-section x=0 (bottom of channel loop) temperature Taver (K)
flow time periods & models of turbulence
t = 0–27 sec
– with k-ω SST
t = 27–45 sec
– with LES
Clogged throat model
Joule heat power
Noticeable
concentration
in zone
near sediments
1.72·107 W/m3
y=0
1.9·107 W/m3
Instantaneous
temperature (t = 45 sec)
x=0
Time-averaged
temperature (t = 27–45 sec)
Overheating temperature
Θ ~ 48 K
(at 250 kW)
for non-clogged model
Θ ~ 32 K
(at 215 kW)
y=0
y=0
y=0
Clogged throat model
x=0
x=0
Local maxima of instantaneous temperature
near the surface of sediments “hill”
are smaller in comparison with values
in channel loop
Noticeable changes of melt flow structure –
intensive upstream
with instantaneous velocity maximum
~1.8 m/s
Noticeable redistribution of
turbulent kinetic energy
and rise of maximum value ~1.9 m2/s2,
which is comparable with TKE value
in channel loop 2.1 m2/s2
x=0
Build-up channel model
Maximum of instantaneous temperature Tmax (K) and angle α (˚) of its position for y = 0
Averaged for cross-section x=0 (bottom of channel loop) and for cross-sections
z=0.394 m (outlet of narrowed left channel branch to throat) temperature Taver (K)
flow time periods & models of turbulence
t = 0–60 sec
– with k-ω SST
t = 60–90 sec
– with LES
Build-up channel model
Joule heat power
6.7·107 W/m3
Noticeable
concentration
in build-up zone
1.62·107 W/m3
y=0
y=0
Instantaneous
temperature (t = 90 sec)
Time-averaged
temperature (t = 85–90 sec)
Overheating temperature
Θ ~ 37 K
(at 223 kW)
for non-clogged model
Θ ~ 32 K
(at 215 kW)
y=0
y=0
Build-up channel model
y=0
y=0
The absence of melt overheating zone
in narrowed channel branch
may be explained by extremely intensive
melt flow near outlet to throat
y=0
Maximum values of instantaneous velocity
component, which is perpendicular
to the outlet cross-section
of narrowed left channel branch,
are extremely larger (up to 2–4 times)
than ones for right channel branch
Channel left outlet is zone
of prevailing generation
of turbulent kinetic energy –
the maximum values of TKE are ~ 4.7 m2/s2
(the value in channel loop
~ 2.1 m2/s2)
Characteristic parameters
of computed models
Clogged
throat model
Build-up
channel model
Non-clogged
model
250
1.9·107
throat bottom
• position of maximum
at sediments
base
Time-averaged temperature (K):
• maximum value
~1864
in the channel
• overheating temperature
~48
Velocity (m/s)
• instantaneous velocity’s
~1.8
maximum in clogging
zone
223
6.7·107
narrowed zone
of left channel
branch
215
1.74·107
channel loop
zone facing
yoke
~1832
~1805
~37
~32
~3.0
~1.7
(channel
outlet)
from –0.066
till 0.021
from –0.075
till 0.093
from –0.097
till 0.092
–0.020
–0.009
–0.028
Joule heat power
• integral (kW)
• maximum value (W/m3)
• fluctuations in time of
transit velocity
(x-component of velocity
area-averaged
for cross-section x=0)
• time-averaged value
of transit velocity
Conclusions
√ The results of numerical modelling of physical fields
distributions in industrial CIFs with build-up channel and clogged
bottom of throat show, that their parameters noticeable differ
from characteristic of non-clogged CIF. The anomalies may
negatively influence on CIF operation.
√ As anomaly of chosen field (e.g. Joule heat maxima) does not
automatically indicate the cause of anomaly of another physical
field (e.g. local overheating), for estimations of CIF clogging
sequences it is necessary the application of complex analysis of
physical fields.
√ Presented results of research show the effectiveness of LES
study of industrial CIFs with geometry, which has been
noticeably varied during operation period due to non-conductive
build-up, clogging or erosion of ceramic lining and especially for
CIFs with extremely narrowed channel branch.
Thank you for attention!
The current research was performed
with the financial support of the ERAF project
of the University of Latvia,
contract No. 2011/0002/2DP/2.1.1.1.0/10/APIA/VIAA/085
EIROPAS SAVIENĪBA
IEGULDĪJUMS TAVĀ NĀKOTNĒ
HES-13 – International Conference
on Heating by Electromagnetic Sources
May 21-24, 2013
Padua, Italy