In the first of the 2015-16 Distinguished Speaker Seminar Series, we have Professor Jeff Morris speaking on September 28, 12:00 – 1:00pm, Room 202 CHBE. All are welcome to attend.
Professor Morris is from the Levich Institute and the Department of Chemical Engineering at The City College of New York. His seminar is on “Extreme transitions of flow properties in mixtures: discontinuous shear thickening and hydrate jamming“.
This talk will discuss two quite different but equally extreme transitions in flow properties observed in dispersed multiphase mixtures. The first discussion will describe a simulation study of abrupt or “discontinuous” shear thickening (DST), which occurs as shear rate is increased in near-hard sphere suspensions at large solid fraction. For many years, DST has been known, and popular videos of running on “oobleck” (cornstarch suspended in water) are found on-line. Yet the fundamental basis has been mysterious and controversial. A simulation based on a quite minimal model—including viscous, electrostatic repulsion and contact frictional interactions between particles—has been shown to reproduce DST as the rate is increased. The contact network between the particles is found to change dramatically as the critical shear rate is surpassed, providing a microstructural basis for the extreme transition.
In the second discussion, the property variations of hydrate-forming water-in-oil emulsions will be described based on experimental observations. This is a critical problem in petroleum pipeline transport where a transition occurs due to a reaction as time progresses. Hydrates are solid crystalline compounds formed by water and small organic molecules (we focus on cyclopentane) at low temperatures; they form a solid layer at the water-oil interface of emulsified drops. Morphology of the hydrate depends on the stabilizing surfactant, but is typically needle-like and porous. The developed porosity of the solid hydrate is critical: even modest internal phase (water) emulsions can “jam”: the low-viscosity emulsion develops a large viscosity and eventually a large yield stress as hydrate formation progresses—much like the undesirable plugging of pipelines. The rheological properties will be correlated to direct imaging of the hydrate crystal growth at a water-oil interface to illustrate the role of the hydrate porosity in this extreme transition.