liquid metal free surfaces under ac magnetic fields
DESCRIPTION
Liquid metal free surfaces under AC magnetic fields. Y. Fautrelle EPM lab./CNRS/Grenoble Polytechnic Institute Outline: introduction static deformations surface motions conclusions. Context. Industrial : In metallurgical applications the free surface is the key-point : - PowerPoint PPT PresentationTRANSCRIPT
Liquid metal free surfaces under AC magnetic fields
Y. FautrelleEPM lab./CNRS/Grenoble Polytechnic Institute
Outline: introduction static deformations surface motions conclusions
Context
Industrial :
In metallurgical applications the free surface is the key-point :
pollution (oxidation), inclusion entrapment
contact between melt and crucible
mass transfers and refining (degassing, alloying …)
Scientific :
full magnetohydrodynamic coupling
Static deformations
The electromagnetic pressure is responsible for a static free surface deformation :
dome effect in induction furnaces axisymmetric shaping
levitation
but symmetry breaking may occur according to the aspect
ratio highly non-symmetric patterns
Static deformations (ACHF)
Domes are oftenly axisymmetric
static dome-shape deformation of an aluminium free surface under the effect of a AC magnetic field, f = 7.5 kHz, cold crucible melting
Static levitation of Al (ACHF=10 kHz)
Static levitation (ACHF=15 kHz)
titanium drop in a cold crucible (slighly unstable)
Static deformations (ACHF)
Axisymmetric shaping : not at all !
coil
cold cruciblesemi-levitatedliquid blob
“Static dome” in a semi-levitation cold crucible; the liquid is a nickel-base alloy; pool diameter is 60 mm, electric current frequency is 30 kHz
Scheme of the apparatus
coil
liquid metal drop 60 mm
substrate
Static deformations of a flat gallium drop (ACHF)
The free surface may take complex static shapes R = 3cm, f = 14 kHz
B = 0 - 40 mT
Static deformations of a flat gallium drop (ACHF 14 kHz + ACLF 0.5 Hz)
Free surface motions (ACLF)
Low frequency magnetic fields generate various types of surface waves
Forced (axisymmetric) waves
Unstable (non-symmetric) resonant waves
symmetry breaking
digitation
emulsion
gallium circular drop (ACLF=1.5 Hz)simple transition axisymmetric azimuthal
B = 0.15 T
Stability diagram of a mercury drop
50
100
150
200
250
1 1,2 1,4 1,6 1,8 2 2,2 2,4
fréquence (Hz)
inte
nsité
du
cour
ant i
nduc
teur
(A
)
mode 4mode 5mode 6mode 7In
duct
or c
urre
nt (
A)
Frequency (Hz)
f5 f6f4 f7
gallium circular drop (ACLF + DC)the azimuthal instability is suppressed
BDC = 1 - 2 T BAC = 1 - 15% BDC
gallium elongated drop (ACLF = 2Hz)simple transition saussage type
gallium elongated drop (ACLF)simple transition snake-type
Oscillations of a gallium drop (ACLF)
« big bang »
Emulsion of a gallium drop (ACLF)droplet formation
Increase of the perimeter
A being almost constant, increase of the surface area occurs through an increase of the drop perimeter p
thus let us consider the non-dimensional perimeter
NB : for a circle p+ = 2= 3.54
App /
A
Evolution of the non-dimensional perimeter versus the coil current
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,4 1,6 1,8 2 2,2
log (I)
log
(p+)
2/3
Energy balance
Magnetic energy : with vol = h a2, A p l
Surface energy :
thus :
vol220 lBEm
AhpEs
3/20
3/1320/ B
aBApp
l
A
conclusions
It is possible to generate surface by
resonant effectsby single frequency systemsby two frequency systems
It is possible to create functions
stirring emulsion
DC magnetic field component is
stabilizing
AC magnetic fields may be destabilizing
even at high frequencies