1. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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

2. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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. Forschungszentrum Rossendorf SFB 609FLOWCOMAG Electrically conducting fluids:liquid metals, semiconductor melts, electrolytes MHD = NSE + Lorentz Force where Context Volume force : - nice tool to play with the flow - can be arranged as needed - contactless action, perfectly controllable - several applications, industrial requests

4. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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 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 Basic Idea: Tailored magnetic field systems

5. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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

6. Forschungszentrum Rossendorf SFB 609FLOWCOMAG PbBi bubbly flow at T  270°C Velocity measuring technique (example)

7. Forschungszentrum Rossendorf SFB 609FLOWCOMAG Experimental platform for combined AC and DC magnetic fields MULTIMAG

8. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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 4)Melt extraction of metallic fibers 5)Seawater flows 6)Electromagnetic levitation

9. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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. Forschungszentrum Rossendorf SFB 609FLOWCOMAG Float-zone crystal growth 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 Solution: secondary coil with phase shift acting as a pump Realization at IFW Dresden

11. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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. Forschungszentrum Rossendorf SFB 609FLOWCOMAG Industrial Al investment casting Problem: high velocities lead to entrapment of oxides and gas bubbles Solution: Magnetic brake by a) DC field done b) AC pump in progress Magnetic control of the filling process Material: Al-Si-alloys

13. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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. Forschungszentrum Rossendorf SFB 609FLOWCOMAG Electromagnetic levitation DC-current added to the levitating coil DC-field provided by permanent magnets

16. Forschungszentrum Rossendorf SFB 609FLOWCOMAG 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