Supercritical fluids, oscillatory flow, and partially saturated porous media by magnetic resonance microscopy

Abstract

The research presented in this dissertation used Magnetic Resonance (MR) techniques to study fluid dynamics in complex systems. The systems investigated were critical and supercritical fluids, partially saturated porous media, and oscillatory flow. Supercritical fluids (SCF) are useful solvents in green chemistry and oil recovery and are of great current interest in the context of carbon sequestration. Flow in partially saturated porous media and the resultant hydrodynamics are important in fields including but not limited to hydrology, chemical, medical, and the petroleum industry. Lastly, Pulsatile and oscillatory flows are prevalent in many biological, industrial, and natural systems. Displacement propagators were measured at various displacement observation times to quantify the time evolution of dynamics in critical and supercritical fluid flow. In capillary flow, the critical phase transition fluid C2F6 showed increased compressibility compared to the near critical gas and supercritical fluid. These flows exhibit large variations in buoyancy arising from large changes in density due to very small changes in temperature. Ensemble averaged MR measurements were taken to observe the effects on a bead pack partially saturated with air under flowing conditions of water. Air was injected into the bead pack as water flowed simultaneously through the sample. The initial partially saturated state was characterized with MR imaging density maps, free induction decay (FID) experiments, propagators, and velocity maps before the water flow rate was increased. After the maximum flow rate, the MR imaging density maps, FID experiments, propagators, and velocity maps were repeated and compared to the data taken before the maximum flow rate. The work performed here showed that a partially saturated single phase flow had global flow dynamics that returned to characteristic flow statistics once a steady state high flow rate was reached. A system was constructed to provide a controllable and predictable oscillatory flow in order to gain a better understanding of the impact of oscillatory flow on Newtonian and non-Newtonian fluids, specifically water, xanthan gum (XG), polyacrylamide (PAM) colloidal suspensions. The oscillatory flow system coupled with MR measured the velocity distributions and dynamics of the fluid undergoing oscillatory flow at specific points in the oscillation cycle.