Rotational frequency selective nuclear magnetic resonance imaging of cylindrically sheared fluids
Abstract
Nuclear magnetic resonance (NMR) imaging techniques have been developed to provide information about the dynamic properties of fluids undergoing Couette flow shearing in the annulus between two concentric cylinders. The NMR signal properties of fluids undergoing solid body rotation in a magnetic field whose strength is linearly dependent on one spatial dimension transverse to the axis of rotation have been investigated. The results are extended to describe the NMR signal properties of a fluid experiencing Couette flow shearing. The flow is treated as a continuum of annular fluid regions each rotating as a solid body whose rotational frequency is dependent on the radius of the annular region. Fluids rotating as a solid body in a linearly gradient magnetic field exhibit oscillatory NMR frequencies. Fourier transformation of a frequency oscillated signal results in a series of frequency bands. The separation between adjacent bands is equivalent to the frequency at which the NMR frequency is modulated. Couette flow shearing produces a continuum of bands whose line widths and intensities are dependent on the distribution of rotational frequencies. Hahn spin echo radio frequency pulses can be used to label the signal in the Couette flow profile whose NMR frequency oscillation is equal to the inverse of the time separation between the excitation pulse and the spin echo pulse. The direction of the field strength variation can be rotated synchronously with the sample to extract the radial dependence of the flow velocity. Solutions of Hexadecyltrimethylammonium salicylate exhibit pronounced non-Newtonian properties. The rheological and molecular behavior of non-Newtonian fluids under Couette flow shearing can be examined by magnetic resonance imaging. These viscoelastic solutions did not exhibit stable Couette flow. The source of the instabilities is unknown.
Degree
Ph.D.
Advisors
Grutzner, Purdue University.
Subject Area
Mechanical engineering|Polymers
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