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Flow Control by Tailored Magnetic Fields (FLOWCOMAG)

April 1-2, 2004 Jointly organized by: Forschungszentrum Rossendorf (FZR) TU Dresden In frame of: Collaborative Research Centre SFB 609 (supported by DFG) Some introductory remarks G. Gerbeth Context, Basic Ideas, Some Examples.

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Flow Control by Tailored Magnetic Fields (FLOWCOMAG)

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  1. April 1-2, 2004 Jointly organized by: Forschungszentrum Rossendorf (FZR) TU Dresden In frame of: Collaborative Research Centre SFB 609 (supported by DFG) Some introductory remarks G. Gerbeth Context, Basic Ideas, Some Examples Flow Control by Tailored Magnetic Fields (FLOWCOMAG)

  2. Basic and applied studies on Magnetohydrodynamics (MHD): 20 years tradition at FZR 10 years tradition at TU Dresden (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 supported by DFG supposed to last 11 years with ~ 1.3 Mio €/a Context

  3. 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

  4. 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

  5. 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

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

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

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

  9. 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

  10. Float-zone crystal growth Solution: secondary coil with phase shift acting as a pump Usual HF heater gives double-vortex in molten zone Concave phase boundary is bad Goal: modified flow field in order to change the solid-liquid phase boundary Realization at IFW Dresden

  11. 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

  12. Industrial Al investment casting Magnetic control of the filling process Material: Al-Si-alloys Problem: high velocities lead to entrapment of oxides and gas bubbles Solution: Magnetic brake by a) DC field  done b) AC pump  in progress

  13. Melt extraction of metallic fibers Magnetic stabilization of: the free surface (global DC field) + the meniscus oscillations (ferromagnetic edge) Real process: Model experiment Results: red – no magnet steel fibers with SnPb green – with magnetic control

  14. Electromagnetic levitation Principle Pronounced rotations and oscillations Goal: Stabilization of the probe Solution: Superimposed DC field no strong field needed, but careful spatial design

  15. Electromagnetic levitation DC-current added to the levitating coil DC-field provided by permanent magnets

  16. Summary Flow control by magnetic fields: nice tool to modify velocity fields • inverse approach: challenging task • Several industrial requests, short bridge to applications • Closer relation between communities of optimization/control and MHD very attractive • Right time for FLOWCOMAG

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