Yoshihide Mawatari, Maya Adachi
The effects of vertical mechanical vibration on bubbling behavior and particle migration in a tapered fluidized bed were experimentally investigated using a two-dimensional apparatus that enabled direct visualization of bubble motion and particle migration. Glass beads with a mean diameter of 54 μm were used as the fluidizing particles. The vibration frequency was fixed at 40 Hz, and the vibration amplitude was varied to clarify the amplitude-dependent changes in bubbling behavior and particle migration. Non-monotonic trends were observed in the hydrodynamic characteristics of bubbling and particle migration. The minimum fluidization velocity decreased steeply with increasing vibration amplitude up to 0.15 mm and then slightly increased at higher vibration amplitudes. At a given gas velocity, the average bubble diameter in the core region initially decreased with increasing vibration amplitude up to 0.1 mm and subsequently increased with further increases in vibration amplitude. In addition, vibration modified the bubbling behavior by altering the bubble-ascending paths in the core region. The extent of the intrinsic particle-migration region increased with vibration amplitude up to 0.25 mm and then decreased when the vibration amplitude exceeded this value, reflecting changes in the spatial extent of the bubbling region induced by vibration. Both the particle-migration velocity and the particle mass flow rate were strongly influenced by variations in bubble diameter and the intrinsic particle-migration region. Moderate vibration effectively suppressed the formation of stagnant regions near the sidewall, thereby promoting particle migration in the annulus region of the bed, whereas excessively strong vibration induced a secondary particle circulation loop that hindered overall particle circulation. The findings provide practical guidance for selecting optimal combinations of vibration intensity and gas velocity in tapered fluidized beds.