Picture of the surface of granular material flowing downward from left to right. A pair of these pictures, taken at a very small time delay, are used to get the velocity vectors.
Laboratory for
Applied Fluid Dynamics
Northwestern University, Evanston, Illinois
Picture of the surface of granular material flowing downward from left to right. A pair of these pictures, taken at a very small time delay, are used to get the velocity vectors.
Granular mixing and de-mixing is of immense practical importance. Vast amount of granular materials are mixed in many industries, including the pharmaceuticals, food, polymers, semiconductors and cement industries. Unlike a flowing fluid, there are no standard equations to exactly decribe the flow of a flowing granular material. There has been very limited study in this field and it is still far from developed. In collaboration with Prof. Julio Ottino, our research focus is to experimentally measure the flow dynamics in a rotating tumblers.
Granular material inside a tumbler
can be divided into two parts: Bulk body and the flowing layer. The bulk undergoes
solid body rotation and the velocity profile for this case is trivial. Flowing
layer, however, is central to the understanding of mixing and segregation. Inspite
of its importance there have been only a few studies to measure the velocity
profile of granular material inside the flowing layer. We have used Particle
Tracking Velocimetry (PTV) in conjunction with Particle Image Velocimetry (PIV)
to measure the particle displacement, velocity field, and number density in
granular flows and also their relation with parameters such as particle size
and angular velocity of the tumbler.
Line segments are velocity vectors obtained from PTV measurements and analysis. The orientation of the line segment shows the direction of a particle's motion; the length of the line segment is proportional to the velocity of the particle. Only a small portion of the flowing layer is captured for PTV analysis as is shown in the inset.