A NEW TECHNIQUE FOR DIFFERENTIATING BETWEEN DIFFUSION AND FLOW IN GRANULAR MEDIA USING MAGNETIC-RESONANCE-IMAGING

We have shown that a simple nuclear magnetic resonance spin-tagging sequence for spatial encoding of the longitudinal magnetization, combined with an imaging sequence, can be used to measure flow and diffusion in granular materials. Using this technique, experiments have been performed to study flow and diffusion profiles during convection induced by the vertical shaking of a container (39 mm diameter) filled with a granular medium. We have shown that maximum diffusion and displacements occur in a thin boundary layer near the container's walls. The observed flow profiles are predominantly flat with relatively small positive displacements across the container with the exception of the boundary layer, where increasingly negative displacements are observed as the container's edges are approached. (C) 1995 American Institute of Physics.