Abstract
When a horizontal disk was rotated within a particle bed, there appeared three different zones above the rotating disk: The central one (inner rigid zone) rotated together with the disk, whereas the peripheral one (outer rigid zone) remained stationary. In the intermediate one (deformation zone or velocity-gradient zone), the velocity of particles varied from zero to that of the inner rigid zone. The shape of these zones and the torque needed for rotating the disk were affected by the rotation speed of the disk, the bed height, the size of the disk, and the flow velocity of the gas supplied from the bottom of the bed. The interrelation between the shape of these three zones and the torque requirements was discussed.
