Toward a Grand Challenge in Powder Flows: The Effect of Material Properties, Boundary Conditions and Shear Rate on Fluctuations and Stress Fields in Flowing Powders.

We report here on work performed on the project in its third year ending October, 2009. Two previous reports have been submitted to IFPRI in 2006 and 2008, respectively. The present research is focused on the study of Powder Mechanics and the ultimate goal is to develop a quantitative description of active flows of a wide variety of powders. The study is centered on the slow, frictional and the dense, “intermediate” regimes of flow where both frictional and inertial effects are important. The novelty of the project is the study of a large range of materials and flow geometries to gain meaningful insight. We report on a series of materials from simple (round beds) to complex (fine, odd-shaped and elastic), used in an axial-flow Couette, high shear mixer, in a centripetal geometry characteristic of a “spheronizer and two hopper flows with a funnel and a flat bottom, respectively to measure stresses and their fluctuations as a function of geometry and shear rate. The main novelty during this year is the measurement of porosity (void fraction) and porosity distribution in the flowing material using a capacitance probe in addition to stress measurements.