Particle motion in gas-fluidized granular systems by pulsed-field gradient nuclear magnetic resonance.

Nuclear magnetic resonance k-space and q-space imaging methods were applied for the first time to monitor the time-averaged density variations and the random motion of granular particles in the presence of gas flow of variable velocity in a model gas-fluidized bed reactor. The transitions toward fluidization, bubbling phase, and slugging phase are visible as sudden changes in the density and the root mean-squared displacement. The onset of these transitions is shown to depend on the particle sizes for a given cell geometry. The effective diffusion coefficients are measured and the distributions of particle displacements, or propagators, are presented.