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Title: Magnetic resonance imaging of fluid flow in a concentric cylinder rheometer
Author: Hanlon, A. D.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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The shear field created by differential rotation of two concentric cylinders of different diameters has for many years been used as the basis of viscometers, the fluid viscosity being calculated from bulk measurements of the torque on one cylinder and the rate of rotation. Powerful as it is, this type of rheological characterisation is often limited by a lack of knowledge of the precise flow conditions at the fluid boundaries and by flow or thermally induced structural inhomogeneity within the sample. The ability to visualise flow fields within a shearing sample is highly desirable in such cases. This thesis reports the development of a protocol which combines Nuclear Magnetic Resonance (NMR) fluid velocity measurement and data analysis, which allows the velocity profile within the annular gap between two concentrically rotating cylinders to be measured. A temperature controlled, concentric cylinder, Couette flow rheometer, which is compatible with the demands of high spatial resolution (50μm) Magnetic Resonance Imaging (MRI) is also described. A range of pulsed-field-gradient (PFG) based NMR imaging strategies for rapid velocity measurement have been evaluated and measurements made using each technique validated using a Newtonian fluid (water) undergoing Couette flow. This optimised measurement protocol has been used to study the temperature and shear-rate dependent flow properties of several fluids of relevance to the food industry. The velocity profiles across the fluid-filled gap were measured, the resulting data were then fitted using the power law model, and comparisons made with conventional stress-strain viscometry measurements. Newtonian flow, shear-thinning (pseudoplastic) behaviour, apparent wall slip and Taylor vortices have all been observed. The technique has also been applied in conjunction with NMR relaxometry to the study of time-varying phenomena which result from changes in sample temperature under shear and prolonged shearing at constant temperature. The combination of hardware and optimised NMR acquisition described complements conventional rheometry measurements and provides information which is not available from any other measurement technique.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available