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

Reduced operation life time of CIF channel

caused by erosion, infiltration and in particular

clogging (build up formations) of the ceramic lining

Existing problems

in Channel Induction Furnace (CIF)

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.

Schemes of build-up formation*

Existing problems in CIF

throat channel outlet

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...

* (Williams D.C. et al., 2007)

Computed models of industrial CIF

Build-up channel model –

CIF with narrowed (25%)

left channel branch

Geometry for modelling of EM field

Clogged throat model –

CIF with sediments

in form of “hill”

Non-clogged model –

CIF original design

Inductor current amplitude is fixed at 1850 A

Peculiarities of numerical computations

Structured mesh for HD and thermal fields:

• software package ANSYS ICEM 14.0

• number of elements ~ 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

EM field, Lorentz force and Joule heat:

• software package ANSYS Classic 14.0

• number of elements ~ 1–1.5 million

Peculiarities of numerical computations

Parameters under control:

√ Courant number C

Anomalies of velocity field: build-up channel model –

near outlets to throat for left narrowed and right channel branches

zzyyxx evevev

yyxx evev

zv

Non-clogged model – CIF original design* flow time t = 0–700 s

√ long-term oscillations’ periods for Tmax and α

√ time delay between extremes

of Tmax position α and Tmax itself –

τ ~ 40 sec

sec 163 ~oscil

T

osciltt max

Temperature distribution in the channel for y=0: maximum Tmax and its position α

√ Tmax lags in phase in comparison with α

√ overheating temperature

Θ ~ 32 K

√ time-averaged transit velocity for x=0

cm/s 2.8 ~vavertrans

throatchannel TT

* 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

flow time periods & models of turbulence

t = 0–27 sec – with k-ω SST

t = 27–45 sec – with LES

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)

Clogged throat model

1.72·107 W/m3

y=0

Instantaneous

temperature (t = 45 sec)

Joule heat power

Noticeable

concentration

in zone

near sediments

Overheating temperature

Θ ~ 48 K

(at 250 kW)

for non-clogged model

Θ ~ 32 K

(at 215 kW)

Time-averaged

temperature (t = 27–45 sec)

1.9·107 W/m3 x=0

y=0 y=0

y=0

Clogged throat model

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

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

x=0

x=0

x=0

Build-up channel model

flow time periods & models of turbulence

t = 0–60 sec – with k-ω SST

t = 60–90 sec – with LES

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)

Build-up channel model

Instantaneous

temperature (t = 90 sec)

Joule heat power

Noticeable

concentration

in build-up zone

Overheating temperature

Θ ~ 37 K

(at 223 kW)

for non-clogged model

Θ ~ 32 K

(at 215 kW)

Time-averaged

temperature (t = 85–90 sec)

1.62·107 W/m3

6.7·107 W/m3

y=0 y=0

y=0 y=0

Build-up channel model

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)

The absence of melt overheating zone

in narrowed channel branch

may be explained by extremely intensive

melt flow near outlet to throat

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

y=0 y=0

y=0

Characteristic parameters

of computed models Clogged

throat model Build-up

channel model Non-clogged

model

Joule heat power • integral (kW) 250 223 215 • maximum value (W/m3) 1.9·107 6.7·107 1.74·107

• position of maximum throat bottom at sediments

base

narrowed zone of left channel

branch

channel loop zone facing

yoke

Time-averaged temperature (K):

• maximum value in the channel ~1864 ~1832 ~1805

• overheating temperature ~48 ~37 ~32 Velocity (m/s) • instantaneous velocity’s maximum in clogging zone

~1.8 ~3.0 ~1.7

(channel outlet)

• fluctuations in time of transit velocity (x-component of velocity area-averaged for cross-section x=0)

from –0.066 till 0.021

from –0.075 till 0.093

from –0.097 till 0.092

• time-averaged value of transit velocity –0.020 –0.009 –0.028

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.

HES-13 – International Conference

on Heating by Electromagnetic Sources

May 21-24, 2013

Padua, Italy

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

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