Operation for Fine Particle Dispersion in Shear-Thinning Fluid in a Stirred Vessel

概要

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Particle dispersion in shear-thinning fluid in a stirred vessel with a turbine blade impeller was investigated experimentally. An aqueous solution of carboxymethylcellulose (CMC) was used as a non-Newton fluid having a weak shear-thinning rheological property. Initially, polymethylmethacrylate (PMMA) fine particles of 8-20 µm were inserted just below the surface of stationary fluid. Complete dispersion time was defined as the time when no large-scale lumps could be found. At the same time, PMMA particles adsorbed on the surface of micron-sized air bubbles accompanied with the initial input of the particles. With proceeding particle dispersion, particles desorbed from the bubble surface, and the average size of bubbles with PMMA particles decreased. To find an optimized operational condition for mixing, the dispersion process was divided into macroscopic and microscopic. For macroscopic dispersion, high rotational speed was required but it should be kept low enough hat it does not create a cylindrically rotating zone. Low rotational speed was favored to purge air bubbles with accumulated particles for microscopic dispersion.