New possibilities for velocity measurements in metallic melts

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• New possibilities for velocity measurements in
  metallic melts
• S. Eckert, G. Gerbeth, F. Stefani
• Department Magnetohydrodynamics,
  Forschungszentrum Rossendorf
• P.O. Box 510119, D-01314 Dresden, Germany,
  http//www.fz-rossendorf.de/FWS/FWSH
• E-mail s.eckert_at_fz-rossendorf.de

Sino-German Workshop on Electromagnetic
Processing of Materials Oct. 11-13, Shanghai,
China
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Why do we need flow measurements in metallic
melts ?

• ?
• Knowledge about the flow field and the transport
• properties of the flow

• ?
• Optimisation of products, technologies and
  facilities
• better understanding of the process
• validation of CFD models
• on-line control and monitoring

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Current situation
Commercial measuring techniques for liquid metal
flows are almost not available !

• Reasons
• properties of the fluid (opaqueness, heat
  conductivity,..)
• high temperatures
• chemical reactivity
• interfacial effects
• external electromagnetic fields

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Goals

• to develop measuring techniques for liquid metal
  flows at moderate temperatures
• ? model experiments (T ? 300C)
• to extend the range of application towards higher
  temperatures

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Data of interest

• flow rate
• local velocity
• fluctuations, turbulence level
• flow pattern (velocity profiles, 3D-structure)

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List of measuring techniques

• Local probes (invasive)
• Electric Potential Probe (EPP, Vives Probe)
• Mechano-Optical Probe (MOP)
• Ultrasonic methods (non-invasive, but need
  contact)
• Ultrasound Doppler Velocimetry (UDV)
• Inductive methods (contact-less)
• Inductive Flowmeter (IFM)
• Contactless Inductive Flow Tomography (CIFT)
• X-ray radioscopy

• Local probes (invasive)
• Electric Potential Probe (EPP, Vives Probe)
• Mechano-Optical Probe (MOP)
• Ultrasonic methods (non-invasive, but need
  contact)
• Ultrasound Doppler Velocimetry (UDV)
• Inductive methods (contact-less)
• Inductive Flowmeter (IFM)
• Contactless Inductive Flow Tomography (CIFT)
• X-ray radioscopy

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Ultrasound Doppler Velocimetry (UDV)

• Takeda (1987, 1991)
• Commercial instrument
• standard transducers
• (Tmax 150C)
• Measurement of instantaneous velocity profiles

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UDV Measuring principle

• Pulse-echo method
• information about the position
• ? time of flight measurement
• information about velocity
• ? Doppler relation
• (c - sound velocity, fD - Doppler frequency, f0 -
  ultrasound frequency)

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UDV in liquid metals problems

• High temperature
• Acoustic coupling
• Transmission of ultrasonic energy through
• interfaces (channel walls)
• Wetting conditions
• Availability of reflecting particles

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Concept of an integrated probe I
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Concept of an integrated probe II

• Collaboration with the University Nishni-Novgorod
  (Russia)
• Piezoelectric transducer coupled on an acoustic
  wave guide made of stainless steel
• Stainless steel foil (0.1 mm) wrapped axially
  around a capillary tube length 200 mm, outer
  diameter 7.5 mm

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UDV in bubbly flows PbBi
Typical velocity signal of a single rising
bubble Further details see presentation of Ch.
Zhang
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UDV in bubbly flows PbBi
(a)
(b)
PbBi, 250 C, single orifice do 0.5 mm, (a) Qg
0.04 cm3/s , (b) Qg 1.2 cm3/s
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UDV Flows driven by RMF/TMF
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UDV Flow driven by RMF
Streamfunction
Vertical velocity
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UDV Flow driven by TMF
Vertical velocity
Streamfunction
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UDV Flow driven by RMF/TMF
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UDV in CuSn/Al Experimental Set-up

• Rectangular alumina crucible (130 ? 80 mm2)
• melt depth 40 mm
• inductive heater
• melt temperature
• 620C (CuSn), 750C (Al)
• installation of the integrated sensor at the free
  surface of the melt
• Doppler angle 35

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UDV in CuSn/Al Results

• Profiles obtained at two positions
• different signs
• similarity of shape and amplitude

Velocity signal obtained in liquid aluminium by
up-and-down moving of the sensor by hand
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Contactless Inductive Flow Tomography (CIFT)

• An existing flow field will modify an applied
  magnetic field
• BB0b, bRm B0 (Rmµ?Lv)
• e.g. the magnetic field measured outside the
  melt contains information about the flow field
• Rm 10-3 ? b O(?T)

Example crystal growth configuration (Czochralski
method)
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CIFT - Basics

• Bio-Savarts law
• inverse method to reconstruct the velocity field
• additional requirements
• mass conservation (div u 0)
• Tichonov regularization (keeps the mean quadratic
  curvature of the velocity field finite)

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CIFT - Experiment

• 48 Hall sensors
• (KSY44-Infineon, resolution 1 ?T)
• Mechanical stirrer (2000rpm)
• max. velocity 1 m/s

• Cylinder filled with InGaSn
• (D 180 mm , H 180 mm)
• Magnetic field two pairs of Helmholtz coils 10mT

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CIFT - Experiment

• Lid with stirrer and motor

Vessel, electronic equipment
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CIFT - Results
Induced magnetic field for transverse
primary field
Induced magnetic field for axial primary field
Reconstructed velocity field
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CIFT - Results
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Conclusions

• Several measuring techniques exist to determine
  the velocity field in metallic melts
• Successful investigations are under progress to
  extend the application range towards higher
  temperatures
• Promising new developments
• Ultrasound Doppler Velocimetry (UDV)
• Contactless Inductive Flow Tomography (CIFT)