Experimental study of granular convection

Dry granular material confined to a cylindrical vessel convects when subjected to either continuous or discrete vertical oscillations of sufficient intensity. Particles flow upward in the center of the container and fall in a thin stream along the wall. We have studied this motion experimentally in three-dimensional cylinders for a variety of material, container, and vibration parameters using tracer particle techniques and magnetic resonance imaging. By combining these methods, we have characterized both the del,th and radial dependence of the vertical flow velocity. We find that the upward flow velocity along the cylinder axis decays exponentially from the iop free surface into the bulk of the material. This flow decreases and changes direction as the inner container walls are approached, displaying a radial dependence closely approximated by either a hyperbolic cosine or a modified Bessel function of order zero. We propose a simple model of granular convection consistent with these findings.