Anomalous collapse of interacting bubbles in a fluidized bed: A magnetic resonance imaging study

The collapse, or reduction in size to zero volume, of bubbles injected into incipiently fluidized beds was studied using rapid magnetic resonance imaging. The collapse of a smaller lower bubble trailing a larger upper bubble and the collapse of one bubble when two bubbles rose side by side were found to occur. Under the same conditions with the use of finer particles or the injection of an isolated bubble, no collapse occurred. Thus, results indicate that gas leakage into the particulate phase of coarse particles and bubble interaction promote bubble collapse. Furthermore, injection of larger bubbles also resulted in bubbles rising to the bed surface instead of collapsing, indicating that bubbles must be below a critical size in order to collapse. For side-by-side bubbles, bubble collapse is attributed to gas flow channeling to the larger bubble; for consecutive bubbles, bubble collapse is attributed to increased gas leakage in a dilated bubble wake.