(322a) Visualizing Complex Flows in Cellulosic Suspensions Using Magnetic Resonance Imaging

Mixing of high solids cellulosic suspensions for enzymatic hydrolysis has widely been considered the rate limiting step in the production of bio-ethanol. Cellulosic slurries at high solids have been proven to exhibit non-Newtonian behavior. Observing the characteristics of these suspensions throughout a wide range of flows is an important tool for rheological characterization. Analysis of magnetic resonance flow images allows for extraction of velocity profiles and rheological data when coupled with pressure drop measurements. Flow profiles for various cellulosic substrates were measured during different flow regimes in cylindrical pipe flow using magnetic resonance imaging. Qualitative transitions in velocity profiles and pressure drop occur as solids concentration or fiber length is changed. Those changes occur at very different mass fractions for fibers of different mean length. The same changes, however, occur at a narrow range of crowding numbers, suggesting that this parameter is a useful variable for characterizing the flow of biomass suspensions. The asymmetric and smooth shape of some velocity profiles suggests that secondary flows are induced by fiber interactions in the presence of gravity.