Title: The Clogging Transition in Granular Flows

Author (Invited): Kerstin Nordstrom, Mount Holyoke College

Abstract:

Granular materials are ubiquitous, yet we still cannot predict precisely how they will flow or jam. For gravity-driven flow through an aperture (often called a silo or hopper), the empirical Beverloo equation can be found to fit the data, though fit coefficients cannot be predicted theoretically. Above some critical aperture size, the material seems to flow indefinitely. Below, the material will always form a clog, though it cannot be anticipated when the clog will occur. There has been debate over whether this is a meaningful transition or not, as well as the mechanisms that produce a clog. We present work on experimental systems approaching the critical aperture size. Our data is extremely high time and spatial resolution to directly measure particle motions and fluctuations. We find evidence for changing microscopic behavior approaching the critical aperture size, though the evidence does not necessarily imply a true critical point. We also show that we can drastically change the clogging transition with the introduction of intruders into the packing. This suggests that the instantaneous local packing structure might be a key component in anticipating clog formation.