Pointwise observations for rheological characterization using nuclear magnetic resonance imaging

This study focuses on development of a nuclear magnetic resonance (NMR) ima ging based viscometric technique using pulsed gradient NMR for characterizi ng fluid materials under steady tube flow conditions. By simultaneously mea suring velocity profiles and pressure gradients it is possible to character ize complex fluids locally. Shear viscosity-shear rate data, ranging from o ne to over two decades of shear rate from one combined velocity profile/pre ssure drop per unit tube length measurement, are provided for five fluids t hat exhibit both Newtonian and shear thinning characteristics. The resoluti on of the velocity data controls the accuracy of the measured shear viscosi ty whereas the radial resolution prescribes the number of shear viscosity-s hear rate data points and the minimum shear rate. Velocity profile measurem ents with a velocity resolution of 1 mm/s and radial resolutions which prov ided from 22 to 110 spatially resolved velocity data points accurately char acterized fluids for shear rates greater than 0.1 s(-1). Dynamic yield valu es measured from velocity data for a microfibrous cellulose solution were w ithin 2% of those measured with a conventional rheometer using the controll ed shear rate method and a vane attachment. (C) 1999 The Society of Rheolog y. [S0148-6055(99)00601-X].