Investigation of some applications of primitive ferrofluids.

The investigation covers two possible areas of application of
magnetic fluids, one involving the production of torque by means of
rotating magnetic fields and the other the use Of magnetic fluids in the
separation of non-magnetic ores on a density basis. The' emphasis-was
upon the use of cheap, primitive ferrofluids Le'. non-collOidal suspension
of relatively large particles. a
Moskowitz and Rosensweig were the first to report electromechanical
energy conversion with a rotating magnetic field. Their theory is not
confirmed by their experimental results, howevert nor the fact that the
fluid can rotate in the opposite direction to the field. This
phenomenon has been investigated experimentally for a range of field
intensities, wave velocities, particle sizes, volume loading and fluid
viscosities. The torque per unit volume has been found to be related
linearly to the volume loading but-nonlinearly to the frequency of the
supply, field intensity and viscosity. For the primitive ferrofluids the
results clearly indicate a combination of saliency and hysteresis torques.
No satisfactory explanation for the reverse motion of the fluid has been
produced and attempts to quantify the energy transfer have not been
successful. Due to the inherently low permeability of the fluid, the
torque per unit volume is much smaller than for conventional a. c. machines.
Primitive magnetic fluids have also been shown to have potential
in the separation of ores according to their densities. The novelty of
this work is that the particles, which flocculate in the presence of
stationary fields, are kept in suspension by agitation caused by a rotating wave. This agitation also serves to reduce the effective
viscosity which at high volume loading can be high at zero field
conditions. An effective specific gravity of about 12 has been obtained.
The experimental results confirm the theory that the magnetic force in
the linear condition is proportional to the magnetic energy - density gradient
(in space) but with saturation the force is proportional to the field
gradient and independent of body shape. A practical system seems to be
feasible.