Identifying States in Shallow Vibrated Beds

Shallow particulate beds on surfaces vibrating at ca. 25 Hz and an amplitude of a few millimetres display several states, in order of increasing bed depth: two ‘Newtonian states’ in which freely bouncing particles obey simple New tonian mechanics; a ‘coherentexpanded (C-E) state’ in which particles move together in loosely organized packets to form a turbulent shallow layer; and a ‘coherent-condensed (C-C) state,’ either beneath or replacing the C-E state, in which particles move together in a compacted layer. In the C-C state, neighboring particles tend to remain in close company. Which states are present, as well as whether a gap forms beneath the vibrated bed, depends on bed depth and particle and gas properties. Transitions between the states appear to be sharp and quantifiable, but further investigation, both theoretical and experimental, is needed before the transitions are fully understood. The C-E state provides intense solid mixing and appears likely to provide superb contacting of a solid with a gas in the space above a shallow vibrated bed. The C-E state may provide an opportunity for developing a family of microreactors for kinetic studies. The C-C state is characterized by a bulk solid-circulation pattern, generally stable over a long time interval, as well as by a relatively low porosity.