NMR experiments on vibrofluidized and gas fluidized granular systems
This dissertation presents experimental studies of granular media using Nuclear Magnetic Resonance (NMR). Two different processes, vibrofluidization and gas fluidization of granular media, were investigated.
In the first study, we measured the number density profiles and velocity distributions of the particles in a three-dimensional vibration system with pulse field gradient (PFG) NMR and magnetic resonance imaging (MRI) techniques. The experiments were repeated with three different values of N I and two different values of Γ, where N I is the number of layers of particles in the sample cell and Γ is the dimensionless acceleration of the vibration. We found the velocity distribution function is generally non-Gaussian except at the top of the sample. NMR data were fitted to a hydrodynamic theory, which successfully models the density and temperature profiles away from the vibrating container bottom. A temperature inversion near the free upper surface is observed, which is explained by the presence of a non-zero transport coefficient μ in inelastic systems.
In the second study, we applied a fast 1D MRI technique to monitor the bubble motion in a fluidized bed. The measured bubble velocity is in excellent agreement with a model based on a potential flow theory. The number density profiles and the displacement distributions of particle were measured using PFG-NMR and MRI with various gas flow rates at different bed heights. We found no particle motion before bubbles are generated in the bed. The displacement distribution results imply that slugging phase is dominant at higher regions of the bed. The velocity distribution of convective particle flows in bubbling phase is fitted to a simple potential flow model, which shows reasonable agreement.