A new interpretation of viscosity and yield stress in dense slurries: Coal and other irregular particles |
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Authors: | C R Wildemuth M C Williams |
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Institution: | (1) CD Medical, 33014 Miami Lakes, FL, USA;(2) Chemical Engineering Department, University of California, Berkeley, 94720 Berkeley, CA, USA |
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Abstract: | Illinois coal was ground and wet-sieved to prepare three powder stocks whose particle-size distributions were characterized. Three suspending fluids were used (glycerin, bromonaphthalene, Aroclor), with viscosities
s that differed by a factor of 100 and with very different chemistries, but whose densities matched that of the coal. Suspensions were prepared under vacuum, with coal volume fractions that ranged up to 0.46. Viscosities were measured in a cone-and-plate over a shear rate
range 10–3–102 s–1. Reduced viscosity
r = /s is correlated in the high-shear limit (
) with/
M, where
M is the maximum packing fraction for the high-shear microstructure, to reveal the roles of size distribution and suspending fluid character. A new model that invokes the stress-dependence of
M is found to correlate
r well under non-Newtonian conditions with simultaneous prediction of yield stress at sufficiently high; a critical result is that stress and not
governs the microstructure and rheology. Numerous experimental anomalies provide insight into suspension behavior. |
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Keywords: | Suspension rheology non-Newtonian viscosity yield stress coal slurry |
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