Title: Structured Flow Instabilities in Excited Granular Materials

Author (Invited): Christopher Boyce, Columbia University

Abstract:

Granular materials, such as sand or catalytic particles, exhibit behaviors which blend the lines between solids, liquids and gases. External excitation by gravity, vibration or gas flow can induce motion in granular materials, and forces competing with frictional particle interactions often result in instabilities, many of which resemble those in liquids, while some of which exhibit solid-like behavior. Here, we combine gas flow and vibration experimentally to excite grains to form flow instabilities with structured waves, convection cells, gas bubbles or segregation patterns. Computational modeling demonstrates that some of these instabilities are directly analogous to those in Newtonian fluids, while others involve transitions between fluid-like and solid-like behavior in grains to form structured flow. We develop new rheological models of granular flows which incorporate fluid-solid transition to capture these structured flow instabilities and potentially improve modeling of all granular flows. These structured flows are applied to segregation, mixing and heat transport in granular flows to improve mining separations, pharmaceutical production and chemical reactor design.