Colloidal suspension hydrodynamics and transport processes in microcapillary and porous media flows studied using dynamic nuclear magnetic resonance
Fridjonsson, Einar Orn
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The research presented in this dissertation uses Magnetic Resonance Microscopy (MRM) to investigate complex fluid dynamics systems. The systems investigated are colloidal transport in a microcapillary, bifurcation and porous medium, reactive transport in porous medium, transport through beta-lactoglobulin gels and the effect of peptide surfactants on droplet deformation in a Taylor-Couette device. Complex transport phenomena underlies many applications in engineering and thorough understanding of convective and diffusive motion in multiphase systems is important. MRM allows for the investigation of multi-phase transport phenomena noninvasively and can be used to investigate different moments of motion by sequence of the application of magnetic field gradients. The measurement of coherent and incoherent motion separately and the simultaneous measurement of multiple phases (colloids or suspending fluid) is possible. The colloidal flow studies show the effects shear induced migration, deposition, incoherent and coherent motion have on the macro- and microscopic structure of the fluids. Results show the direct effect increased shear has on the onset of secondary and chaotic fluid motion due to microscopic particle-particle and macroscopic fluid-structure interactions indicating the presence of shear thresholds. Reactive transport in porous media is important for understanding the spread of contaminants in the Earth's subsurface. The effect of calcium carbonate precipitation in a model porous medium due to Sporosarcina pasturii growth on the hydrodynamics was measured using MRM. These measurements show an increase in mechanical mixing causing a more rapid asymptote to Gaussian dynamics than for the same system without precipitation. The transport measurements of water with and without NaCl flowing through a homogeneous (pH 7.0) and heterogeneous (pH 5.2) beta-lactoglobulin gels quantifies the hydrodynamic dispersion in the gels and provided direct information on the gel structure noninvasively. Droplet deformation of (36/64)%wt toluene/chloroform droplets in a continuous phase of glycerol inside a Taylor-Couette device with and without surfactants (2%wt Tween60, AM1 and AFD4 peptide surfactants) is measured using a rapid MRM sequence (ROTACOR) which compensates for system rotation. MRM measurements show a restriction to droplet deformation due to the presence of the peptide surfactants.