CFD-DEM Study of Anomalous Collapse of Interacting Bubbles into an Incipiently Fluidized Bed

Computational fluid dynamics – discrete element method (CFD-DEM) recreates the collapse phenomenon of the recent magnetic resonance imaging (MRI) study (Boyce et al., Phys. Rev. Fluids, 2019, 034303) in which one bubble collapses when two bubbles are injected side-by-side into an incipiently fluidized bed, and the other bubble does not collapse and reaches the surface of the bed. Our simulation results reveal the underlying physics behind the collapse phenomenon which was ambiguous in the 2D imaging plane of the experimental results. The 3D visualization of voidage field and gas velocity field from simulations demonstrates that bubble collapses and it does not move out of the imaging plane of the study. Also, our results confirm the hypothesis of the MRI study where there should be a slight difference in size of the bubbles, which causes the gas flow to channel more favorably to the larger bubble. Therefore, the smaller bubble does not receive enough gas flow to channel through it and support its roof which leads to its collapse.
Keywords: CFD-DEM; Fluidization; Bubbles; Collapse; Magnetic Resonance Imaging