Magnetic Resonance Imaging of the Interaction of Bubbles and Jets Injected into Fluidized Beds*

Rapid magnetic resonance imaging (MRI) is used to measure the dynamics of bubbles and jets of gas injected into 3D gas-fluidized beds of granular particles. When two bubbles initially of equal volume rise side-by-side, one bubble collapses while the other maintains its size. This phenomenon is attributed to channeling of gas flow through one bubble, leaving the collapsing bubble with insufficient gas flow to maintain its roof and rise velocity via drag force. When two jets of gas are injected side-by-side, bubbles pinch off from the two jets at alternating times, creating a zipper-like pattern. This phenomenon is attributed to the growth of one jet pushing particles toward the second jet, causing bubble pinch-off from the second jet. The second jet subsequently grows, pushing particles toward the first jet, causing a cyclical pattern to form. Different bubble and jet interaction patterns are seen depending on the size of the particles in the fluidized bed; these differences are attributed to the variation in gas permeability through assemblies of granular particles with particle size.