Magnetic resonance studies of transport in multiphase pharmaceutical delivery and mixing systems

Abstract

In this dissertation research utilizing magnetic resonance methods to noninvasively probe the dynamics and transport properties of novel engineering systems is presented. The systems investigated are an osmotic controlled release pharmaceutical tablet as well as two mixing and reaction devices, a Taylor-Couette device and a jet-in-tube mixer. Magnetic resonance imaging of an osmotic controlled-release pharmaceutical tablet is used to measure water concentration as a function of tablet hydration time. A 1D mass transport model for tablet water hydration directly quantifies whether osmotic or diffusive processes dominate transport and is used to estimate transport coefficients for these processes. Magnetic resonance velocity mapping of Couette and Taylor vortex flow regimes for single and two-fluid systems in a vertically oriented Taylor-Couette device are compared to simulations. For the single fluids, the magnetic resonance experiments and Fluent© computational fluid dynamics simulations show excellent agreement in determining the rotation rate at which the flow transitions from Couette to Taylor vortex flow and the corresponding critical wavelength of the unstable flow. In the two-fluid studies, immiscible fluids are axially stratified in the stable density, heavy fluid on bottom, configuration. In both simulation and experiment, the two-fluid interface is observed to remain in the Couette flow regime after the pure fluids away from the interface have transitioned to the Taylor vortex flow regime, thus indicating a stabilizing force, surface tension, at the interface. A vertically oriented co-current jet-in-tube device with acetone as the jet fluid and water as the tube fluid, operated at low jet Reynolds numbers (Re jet ~ 17), is used to produce a laminar positively buoyant jet, which transitions to an unstable mixing regime, characterized by vortex formation and breakdown in flow visualization experiments. Magnetic resonance velocity mapping and diffusion measurements at varying positions downstream of the jet exit are used to characterize the mixing due to vortex formation and breakup. The buoyancy driven instability which results from introducing the less dense acetone (SG=0.79) into the more dense water (SG=1) in opposition to gravity gives rise to significantly enhanced hydrodynamic dispersion of the two fluids. Non-equilibrium statistical mechanics concepts are introduced as a model for mixing by the formation and decay of coherent vortex structures generated by the buoyant instability.