Sur ce site

Sur le Web du CNRS

Accueil du site > Séminaires > Archives > Année 2010 > Markus Zahn

Flow Phenomena in Ferrohydrodynamic Magnetic Liquids (Ferrofluids) and Electrohydrodynamic Charged and Polarizable Liquids

Markus Zahn

Mardi 26 janvier, à 11h en salle C. Brot.

Continuum electromechanics of ferrohydrodynamic interactions in magnetic liquids (ferrofluids) and electrohydrodynamic interactions between charged and polarizable dielectric liquids will be described with video presentations of simple but instructive and thought provoking experiments. With a brief presentation of magnetic fluid science and technology representative magnetic fluid phenomena include : ferrofluid rise due to magnetization force ; ferrohydrodynamic spike and labyrinth instabilities ; stabilization of the Saffman-Taylor pusher fluid fingering instability where a less viscous fluid pushes a more viscous fluid ; and ferrofluid spiral patterns, flows, and abrupt transitions from a continuous to discrete phase in rotating magnetic fields. Analogous electrohydrodynamic presentations include : Coulombic force on a surface within a more conducting liquid (von Quincke’s rotor) ; spontaneous DC and three phase AC high voltage generation from self-excited electrostatic induction machines (Lord Kelvin’s dynamo using falling water droplets) ; interfacial fluid convection cells driven by interfacial surface charge ; fluid rise due to electrical polarization forces ; electrostatic control of fluid jet profiles ; electric field stabilization of the Rayleigh-Taylor instability of a more dense fluid over a less dense fluid ; and dielectric fluid labyrinth instability. Magnetic fluid analysis will also be presented for plane Poiseuille/Couette flow in alternating and rotating magnetic fields to demonstrate and explain “negative viscosity” phenomena. Confirming torque measurements using a Couette viscometer will be compared to the theory. Magnetic fluid bells, chains, and sheet flows will also be shown as a function of DC magnetic field strength and direction.

Laboratory for Electromagnetic and Electronics Systems, MIT

Invité par E. Lemaire.