MHD Department Institute of Safety Research 2 nd Sino-German Workshop on EPM (Dresden) Experimental studies of bubble-driven liquid metal flows in a static magnetic field C. Zhang, S. Eckert, G. Gerbeth Forschungszentrum Rossendorf, Dresden - Germany

MHD Department Institute of Safety Research Background & Motivation Numerous applications of bubble-driven flows and magnetic fields in metallurgical engineering Combination of gas bubble injections and magnetic fields Comprehensive understandings of such MHD two-phase flows

MHD Department Institute of Safety Research Scalar quantity transportations in MHD flows A static magnetic field might both increase and decrease the heat transfer rate in enclosed thermal convections –T. Tagawa & H.Ozoe, J. Heat Transfer 120, –U. Burr & Mueller, J. Fluid Mech 453, –G. Authie, et al., 2003, Eur. J. Mech. B/Fluids 22, Flow field information are highly desirable How about bubble-driven flow in a magnetic field? Single bubble motion; bubble plume flow

MHD Department Institute of Safety Research Bubble-driven flow: experimental setup Cylindrical container aspect ratio=2.5 Liquid metal – GaInSn Single Ar bubble or bubble plume Q max =8cm 3 /s A vertical longitudinal magnetic field or a horizontal transverse magnetic field, B= T UDV measurements of the vertical and radial component velocity

MHD Department Institute of Safety Research Single bubble rising in a longitudinal magnetic field Rising bubble Bubble wake US transducer

MHD Department Institute of Safety Research Bubble wake modified by the longitudinal magnetic field B=0 B0B0

MHD Department Institute of Safety Research Bubble drag coefficient modified by the longitudinal magnetic field Magnetic interaction number: ratio between electromagnetic and inertial force (N = ) Bubble Eötvös number

MHD Department Institute of Safety Research Bubble velocity oscillation frequency and amplitude modified by the longitudinal magnetic field St = f  d e /u T

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Spatial properties (Q=0.37cm 3 /s) B=0 B=0.06T

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Spatial properties (Q=0.37cm 3 /s) B=0.11TB=0.17T

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Spatial properties (Q=3.7cm 3 /s) B=0B=0.06T

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Spatial properties (Q=3.7cm 3 /s) B=0.11TB=0.17T

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field -Radial component void fraction distribution measurements B Container cross-section view Q=7cm 3 /s

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Temporal properties (Q=4.0cm 3 /s) Q=5cm 3 /s R=0.87

MHD Department Institute of Safety Research Bubble plume-driven flow in the transverse magnetic field - Temporal properties (Q=4.0cm 3 /s) Q=5cm 3 /s R=0.87

MHD Department Institute of Safety Research Summary The non-intrusive UDV measuring technique allows us to look into the opaque liquid metal flows A DC transverse magnetic field modifies both the spatial and temporal properties of the ordinary bubble-driven flow DC magnetic field may enforce flow instabilities! (Continuous casting + EMBR) Potential tools for controlling liquid metal flows in metallurgical engineering

MHD Department Institute of Safety Research Perspectives for future research projects Potential topics of interest: –Liquid metal mixing enhancement (control of heat and mass transfer in bubble plumes) –Gas phase distributions –Free surface stabilization –Continuous casting –… FZR: Capacity of EPM model experiments in metallurgical engineering –Liquid metal model experiments –Magnetic fields (tailored fields  MULTIMAG facility) –Measuring techniques

MHD Department Institute of Safety Research Acknowledgement The research is supported by the Deutsche Forschungsgemeinschaft (DFG) in the form of the SFB 609 “Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry”. This support is gratefully acknowledged by the authors.

MHD Department Institute of Safety Research Magnetic field influence on the liquid velocity distribution in the container meridional plane Q=20sccm

MHD Department Institute of Safety Research Vortex structure evolution in a static magnetic field P. Davidson. 1995, JFM, 299,

MHD Department Institute of Safety Research when the velocity is uniform in the direction of the magnetic field, then current density is a potential, namely so there is no Joule dissipation in such case. Accordingly, the Joule dissipation can be reduced by forming the two-dimensional vortical structures along the magnetic field line direction. D. Lee & H. Choi, JFM, 2001, by taking the curl of both sides and using the equation

MHD Department Institute of Safety Research Bubble drag coefficient modified by the longitudinal magnetic field

MHD Department Institute of Safety Research Bubble velocity oscillation frequency and amplitude modified by the longitudinal magnetic field