PhD Comprehensive Exam Presentation by Schamali Jayaratne, ChBE
- Monday, November 19, 2018 from 2:10pm to 3:00pm
- Roberts Hall, 113 - view map
Large Amplitude Oscillatory Shear (LAOS) Characterization using Rheo-NMR
Abstract: The proposed research explores flow behavior of model and food viscoelastic fluids when subject to a large periodic motion known as large amplitude oscillatory shear (LAOS). This motion induces permanent structural changes in complex fluids, generating nonlinear stress responses. From trying to squirt ketchup out from a bottle to the industrial production of consumer products, which are mostly complex fluids, nonlinear shear regimes are important. Knowing flow characteristics of these fluids under such aggressive deformations is key to designing efficient industrial processes and formulating products to the desired material properties associated with quality. While classical rheology (the study of the flow and deformation of matter) techniques give good estimation of stress-strain bulk flow response, it fails to provide local flow information. The research applies proton () nuclear magnetic resonance (NMR) to measure spatially and temporally resolved velocity information of the fluids. The study of fluid deformations using NMR techniques, called rheo-NMR, is a novel flow measuring technique in that it is non-invasive and can quantify three-dimensional velocity fields in opaque. Flow responses, to LAOS created by a strain controlled portable rheometer drive shaft on pseudo plastic and yield stress fluids like ketchup and yogurt are studied in this research. Newtonian fluids like deionized water, that show no structural rearrangement during flow, are used as controlsfor comparison to complex fluids when subject to similar strains. The data provide the first direct measurement of spatiotemporal velocities of fluids subject to LAOS, providing the missing link between bulk stress and strain responses and local flow responses.
- Department of Chemical and Biological Engineering