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Time-dependent shear flow of artificial slurries

University of British Columbia

An experimental method was developed for characterizing time-dependent slurries of elongated particles in a coaxial cylinder viscometer which has a wide gap between the inner rotating cylinder and the stationary cup. A model slurry system was studied; it consisted of a dispersed phase of regularly sized nylon fibers and a dispersing medium of an aqueous solution of polyethylene glycol with dextrose and sodium chloride, each of whose effects on the time-dependent nature of the slurry could be examined separately. The slurry gelled in the viscometer on standing. The time-variation of shear stress exerted on the wall of the inner cylinder rotating at a constant angular velocity was recorded as a stress decay curve. It was found that only a part of the gap between the cylinders of the viscometer flows under shear, and that the thickness of the flowing layer increases with time and approaches an equilibrium value. The time-variation of the thickness of the flowing layer Rx(t) as well as the shear stress decay was measured for fifteen slurries. An empirical reaction-rate type model was constructed for the time-variation of the thickness of the flowing layer Rx(t). A second order-zero order reversible reaction model fitted the experimental data well. The three fitting factors of the model were the equilibrium value of the thickness of the flowing layer Rx∞, and the two rate parameters kf/B and B/A. These factors (Rx, Kf/B, and B/A) were correlated with particle length-to-diameter ratio, volume fraction of particles in the slurry, and angular velocity of the rotating cylinder.

Text

2010-03-05

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http://hdl.handle.net/2429/21544

Chemical and Biological Engineering

University of British Columbia

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