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The influence of magnetic separation on the magnetoviscous behaviour of ferrofluids.
S. Thurm
, S. Odenbach
ZARM, University of Bremen, Am Fallturm, 28359 Bremen
Abstract
The sizedistribution of nanosized magnetic particles in ferrofluids is of fundamental significance if the fluid is subjected to shearflow under the influence of an applied magnetic field. By magnetic separation it is possible to divide a ferrofluid into two fractions which differ in mean particle size. During the separationprocess large particles and socalled primary agglomerates diffuse to regions which are located in the stronger field, whereas this effect is very weak on smaller particles. After the experiment there are two different fractions: one fraction with lower, and another fraction with higher percentage of bigger particles. Rheological investigations after the separationprocess show the important effect of bigger particles on the magnetoviscous behavior of the fluid. It has been found that the fraction with high percentage of big particles and primary agglomerates shows a strong, field dependent increase of viscosity, which in turn is dependent on the shearrate. The other fraction shows a very weak increase of viscosity, and the shearrate dependence vanishes. Tables 1, Figs 5, Refs 9.
Magnetohydrodynamics 37, No. 3, 291296, 2001 [PDF, 0.19 Mb]
