Time periodic viscosity of concentrated kaolin suspensions at constant shear rates |
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Authors: | Olaf Seidel Frank Bagusat Hans-Jörg Mögel |
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Institution: | (1) Freiberg University of Mining and Technology Institute of Physical Chemistry Leipziger Strasse 29 D-09596 Freiberg, Germany e-mail: olaf@molex.phychsub.tu- freiberg.de, DE |
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Abstract: | Knowledge of the viscosity of concentrated suspensions is required for several technical applications, e.g. process control
in mechanical engineering, casting of ceramics and pipeline transport of solids. Our previous viscometric investigations of
concentrated suspensions showed, under particular shear conditions, an apparent viscosity that was periodic in time for a
constant shear rate and temperature. These results were obtained with rotational viscometers with a set coaxial geometry.
The inner cylinder was rigidly coupled to the viscometer driving axis. In this paper we describe a viscosity time behavior
which was found using another type of coupling. Measurements were performed with rotational viscometers with a non-rigidly
linked inner cylinder (small sample adapter supplied by Brookfield). Using kaolin suspensions of 30% solid mass content, viscosity
oscillations appear. They show a regular time pattern at certain intervals of low shear rates. The amplitudes reach up to
20% of the viscosity mean value. In addition a motion of the inner cylinder away from the coaxial position is observed. This
dislocation is followed by a relocation into the coaxial position. A maximum in the viscosity value is correlated with a maximum
of the dislocation position. The process of dislocation and relocation of the inner cylinder is assumed to be caused by local
anisotropically distributed inhomogeneities, which originate from shear-induced agglomeration and deglomeration of suspended
particles. The motion of the inner cylinder is described by introducing a perturbation term into the equation of motion. The
parameters of the perturbation term are fitted to the experimental data.
Received: 10 September 1998 Accepted: 28 April 1999 |
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Keywords: | Viscosity Concentrated kaolin suspension Rotational viscometer Time dependence Non-Newtonian fluid |
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