EFFECTS OF AMBIENT GASES ON GRANULAR-MATERIALS UNDER VERTICAL VIBRATION

We consider layers of noncohesive granular materials of mean height h subject to vertical vibration z=Acos(ωt). Above γAω2/g1, convection begins, creating a heap of height L. We find that for particles of diameter d<1mm the pressure P of the surrounding gas plays a key role: L=btanh(KP)+c, where b and K depend on h, the gas viscosity, d, γ, and A. Convection is significantly suppressed if the shaker sidewalls are permeable, showing that gas trapped in the granular material is a major source of heaping. We consider criteria to determine when gas effects are relevant. © 1995 The American Physical Society.