Polydisperse Coal Slurry Rheology. Final Report, 15 July 1984-30 September 1986

摘要

A theoretical investigation of the rheological behavior of high concentration, polymodal coal-water slurries is carried out on the assumption that the slurry may be considered to be made up of two relatively distinct particle fractions - a coarse fraction and a smaller fine fraction. The particles in the fine fraction are of micron size and are assumed to behave as a colloidal suspension inc the carrier liquid. The coarse fraction takes up most of the space and its hydrodynamics with respect to the suspension is assumed to be the same as if it were in a pure liquid with the same viscous behavior as the suspension. It is shown that in the limit of low shear rate the suspension microstructure is primarily determined by a balance between the Brownian diffusion forces and surface forces, while in the high shear rate limit viscous forces dominate and generally shift the suspension microstructure towards a lower dissipation configuration. The theory is first applied to truly bimodal suspensions of rigid spherical particles and it is shown that the calculated viscosity of these slurries can be accurately matched to experiment. Based on this biomodal concept, a semi-empirical analytical model and a spatially periodic cell model that both use hydrodynamic lubrication concepts and results from the simpler truly bimodal case, are applied to six high concentration polymodal coal-water slurries with continuous particle size distributions ranging from 0.5 to 300 microns. Comparison of the theory with reported measured viscosities supports the idea that these slurries behave bimodally. A series of experiments with coal were run to separately specify the contributions of the colloidal and coarse particles to the measured viscosity. The results agree very well with the theoretical prediction. 24 refs., 6 tabs. (ERA citation 12:003321)