Adams, Luke Wayne (2009)
Ph.D. thesis, University of Birmingham.
When non-Newtonian fluids are mixed in a stirred tank at low Reynolds numbers caverns can be formed around the impeller. If the fluid contains a yield stress the cavern has a fixed boundary where no flow occurs outside of it. When the fluid does not contain a yield stress a pseudo-cavern is formed, the cavern boundary is not fixed since flow can occur outside of it, but the majority of the flow is present in a region around the impeller. Mixing and cavern formation of a variety of non-Newtonian fluids are studied using experimental techniques and computational fluid dynamics (CFD). Cavern data extracted from both methods are compared with mechanistic cavern prediction models. An adapted planar laser induced fluorescence technique showed that mixing inside of a shear thinning Herschel-Bulkley fluid is very slow. Positron emission particle tracking obtained flow patterns and cavern sizes of three rheologically complex opaque fluids. CFD was able to predict the data obtained from both experimental techniques fairly well at low Reynolds numbers. A toroidal cavern model provided the best fit for single phase fluids but for the opaque fluids all models drastically over predicted the cavern size, with the cylindrical model only predicting cavern heights at high Reynolds numbers.
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