Schematic illustration of the coupled ferrohydrodynamic problem for spin-up flow. The azimuthal velocity component and axially directed spin velocity are obtained for a long column of ferrofluid of external radius subjected to a uniform rotating magnetic field perpendicular to the axis of the cylinder. The magnetic field source is modeled as a -directed surface current distribution , which is backed by a material of infinite magnetic permeability, .
Torque measurements as a function of frequency and amplitude of the applied magnetic field for EMG705̱0 using a spindle volume of .
Experimental velocity profiles for EMG705̱0 and EMG900̱2 ferrofluids. Ultrasonic transducers were placed at half the height of the container. Angles are with respect to the diagonal.
Velocity profiles for (a) EMG705̱0 and (b) EMG900̱2 ferrofluids showing the dependence of flow with frequency for an applied magnetic field of amplitude rms.
Velocity profiles for (a) EMG705̱0 and (b) EMG900̱2 ferrofluids, showing the dependence of flow with amplitude of the applied magnetic field for a frequency of .
Velocity profile for (a) EMG705̱0 and (b) EMG900̱2 ferrofluids using probes placed at four different heights of the container with cover.
Axial velocity component measured for (a) EMG705̱0 and (b) EMG900̱2 ferrofluids using a probe placed on the fixed top cover (-measured from the top).
Startup of spin-up flow for EMG705̱0.
Velocity profiles for EMG705̱0 at different heights in a container without a cover. The negative velocities indicate counter-rotation of fluid and field.
Theoretical (a) translational and (b) spin velocity profile for zeroth, first, and composite asymptotic solution obtained from regular perturbation and with using ferrofluid properties for EMG705̱0.
Log-log plots of the experimental extrapolated wall velocity vs Langevin parameter for EMG705̱0 and EMG900̱2.
Log-log plots of the experimental normalized torque vs Langevin parameter for (a) EMG705̱0 and (b) EMG900̱0 ferrofluids and all their dilutions.
Physical and magnetic properties at room temperature for water and kerosene based ferrofluid.
Estimated magnetic particle diameters and effective relaxation times at room temperature for water and kerosene based ferrofluid.
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