flow control by tailored magnetic fields

Forschungszentrum Rossendorf

Sino-German Workshop on EPMShanghai, Oct. 11-12, 2004

Flow Control Flow Control by Tailored Magnetic Fieldsby Tailored Magnetic Fields

Context, Basic Ideas, Some Examples

Sino-German Workshop on Electromagnetic Processing of Materials (EPM)

Shanghai University, Oct. 11-13, 2004

G. Gerbeth

Forschungszentrum Rossendorf (FZR), Dresden, Germany



Magnetic Fields: Contactless influence on Processes and

MaterialsAttractive R&D topic for the future

Powerful research programs in China and Germany: Cooperation between Chinese and German teams

(serious basis exists already) Exchange of students, Ph.D.’s, postdoc’s Joint R&D projects, joint industrial projects (?)

Support by Sino-German Center for Research Promotion(founded by NSFC and DFG) is gratefully acknowledged

Introduction: Sino-German Workshop on EPM



Basic and applied studies on Magnetohydrodynamics (MHD):- 20 years tradition at FZR- 10 years tradition at Dresden University (TUD)- Local network in Dresden (IFW, Uni Freiberg, FhG, MPI)- Traditional cooperation and Twinning Agreement with

Institute of Physics Riga (Latvia)

Since 2002: Collaborative Research Centre SFB 609 at TUD

“Electromagnetic flow control in metallurgy, crystal growth and electrochemistry”

supported by DFG supposed to last 11 years with ~ 1.7 Mio €/a

Introduction: MHD in Dresden (Germany)



Electrically conducting fluids: liquid metals, semiconductor melts, electrolytes

MHD = NSE + Lorentz Force

where

Context

BjtrfL

),(

)( BvEj

Volume force : - nice tool to play with the flow- can be arranged as needed- contactless action, perfectly controllable- several applications, industrial requests

Lf



Up to now: Forward Strategy – What are the changes if some magnetic field is applied?

Known magnetic field actions: DC fields: Flow damping AC-fields, low frequency: stirring and pumping AC-fields, high frequency: Heating and melting, levitation

MHD Catalogue

Necessary: Transition to inverse approach1) Which flow is desirable?2) Which Lorentz force can provide this?3) How to make this Lorentz force?

Note: flow field often not the goal, just some intermediate agent

Basic Idea: Tailored magnetic field systems



Why now?

1) Strong request from applied side for smart solutions with low effort (Tesla cost money!)

2) powerful community for optimization, control theory, inverse strategies

3) new computer capabilities

4) MHD catalogue is well filled

5) new level of velocity measuring techniques for liquid metal MHD flows (liquid metal model experiments up to T 400°C)

6) new level of experimental tools for superposition of AC and DC magnetic fields

Basic Idea: Tailored magnetic field systems



PbBi bubbly flow at T 270°C

Velocity measuring technique (example)

75 100 125 150 175 200 2250

50

100

150

200

250

300

350

400

bubble

liquid velocity

velo

city

[mm

/s]

depth [mm]



Experimental platform for combined AC and DC magnetic fields

MULTIMAG



Examples for partly going the inverse way

1) Industrial Cz-growth of single Si crystals

2) Float-zone crystal growth

3) Industrial Al investment casting Dr. Eckert

4) Melt extraction of metallic fibers

5) Seawater flows

6) Electromagnetic levitation Dr. Priede



Industrial Cz-growth of single Si crystals

Goals: - larger diameters (200 300)- stable growth process- homogeneous oxygen distribution

Solution: AC fields for flow driving, DC fields for reduction of fluctuations

Combined fields installed at Wacker Siltronic



Float-zone crystal growth

Usual HF heater gives double-vortex in molten zone

Concave phase boundary is bad for the growth of single crystals

of intermetallic compounds

Goal: modified flow field in order to change the solid-liquid phase boundary




Solution: secondary coil with phase shift acting as a pump

Realization at IFW Dresden

Parameters to adjust: Current amplitude and frequency, vertical distance between coils, C1, R1




The principle action of such a two-phase stirrerModel experiments demonstration

Single coil double coil double coil upwards pumping downwards pumping



Optimum: distance crystal radius


Numerical simulations: electromagnetic fields, flow, temperature field

Example: Variation of the vertical distance of the coils

h = 1 mm h = 3 mm h = 5 mm




Growth of NiSi5Pumping action of the double inductor:

downwards upwards




Standard float-zone with double inductor

HoNi22B2C Fe87.5Si12.5 YNi2B2C

Ni95Si5



Extraction of steel fibers Extraction of steel fibers in an open industrial facilityin an open industrial facility

Melt extraction of metallic fibres



Principle of the process

Melt extraction of metallic fibres

• rapid quenching• almost all materials

(intermetallics, too)

• Diameter > 100 mikron• Too broad distribution of fibre diameters



Melt extraction of metallic fibers

Magnetic stabilization of: the free surface (global DC field) + the meniscus oscillations

(ferromagnetic edge)

Model experiment Results: red – no magnet with SnPb green – with magnetic control



Summary

Flow control by magnetic fields: nice tool to modify velocity fields

inverse approach: challenging task Several industrial requests, short bridge to

applications

Essential tools: numerical simulations new class of velocity measuring techniques for

liquid metals „cold“ model experiments

Attractive basis in China and Germany

Right time for a Sino-German Workshop



Outlook for 2005

Joint 15th Riga and 6th PAMIR International Conference on

Fundamental and Applied MHDRiga (Latvia), June 27 – July 1, 2005

http://www.ipul.lv/pamir

German-Chinese Workshop in Dresden: to be discussed

flow control by tailored magnetic fields

Documents