Flow Control by Tailored Magnetic Fields

1. 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 Flow Control by Tailored Magnetic Fields

2. Magnetic Fields: Contactless influence on Processes and Materials Attractive 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

3. 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)

4. MHD = NSE + Lorentz Force where Electrically conducting fluids: liquid metals, semiconductor melts, electrolytes Context Volume force : - nice tool to play with the flow - can be arranged as needed - contactless action, perfectly controllable - several applications, industrial requests

5. Necessary: Transition to inverse approach 1) 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 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 Basic Idea: Tailored magnetic field systems

6. 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 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 strategies3) new computer capabilities 4) MHD catalogue is well filled Basic Idea: Tailored magnetic field systems

7. PbBi bubbly flow at T  270°C Velocity measuring technique (example)

8. Experimental platform for combined AC and DC magnetic fields MULTIMAG

9. Examples for partly going the inverse way • Industrial Cz-growth of single Si crystals • Float-zone crystal growth • Industrial Al investment casting  Dr. Eckert • Melt extraction of metallic fibers • Seawater flows • Electromagnetic levitation  Dr. Priede

10. 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

11. Float-zone crystal growth Goal: modified flow field in order to change the solid-liquid phase boundary Usual HF heater gives double-vortex in molten zone Concave phase boundary is bad for the growth of single crystals of intermetallic compounds

12. Float-zone crystal growth Solution: secondary coil with phase shift acting as a pump Parameters to adjust: Current amplitude and frequency, vertical distance between coils, C1, R1 Realization at IFW Dresden

13. Float-zone crystal growth The principle action of such a two-phase stirrer Model experiments demonstration Single coil double coil double coil upwards pumping downwards pumping

14. Optimum: distance  crystal radius Float-zone crystal growth 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

15. Float-zone crystal growth Growth of NiSi5 Pumping action of the double inductor: downwardsupwards

16. Float-zone crystal growth Standard float-zone with double inductor Ni95Si5 HoNi2B2C Fe87.5Si12.5 YNi2B2C

17. Extraction of steel fibers in an open industrial facility Melt extraction of metallic fibres

18. 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

19. 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

20. 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

21. Outlook for 2005 Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD Riga (Latvia), June 27 – July 1, 2005 http://www.ipul.lv/pamir • German-Chinese Workshop in Dresden: to be discussed