Air-driven reverse buoyancy

Air-induced fluidization in vibrated granular beds can be responsible of the phenomenon of reverse buoyancy. We show that the air flow induced across the bed, as the gap in the bottom of the cell evolves, can fluidize the bed in a similar way as in gas-fluidized static beds and consequently a buoyancy force can arise. To quantify this mechanism we use Krollʹs model.