Motion of Ferrite Particles under a High Gradient Magnetic Field in a Magnetic Fluid Shaft Seal

Abstract

In order to investigate the time dependence of sealing ability of a magnetic fluid shaft seal, we measured the burst pressure ΔP, at which the seal was broken, as a function of the elapsed time t under the applied magnetic field. The burst pressure ΔP increases in proportion to √t in the region t<104 s. This result is ascribed to the temporary increase in number density of particles around the top of the pole-tip in proportion to √t. This can be theoretically explained by the solution of a diffusion equation of ferrite particles in a magnetic field. Besides, at t=0, the experimental burst pressure agrees with the calculated value from the conventional theory in which the magnetic fluid is approximated as a continuum.