(163b) Complex Flows of Cellulosic Fiber Suspensions Visualized Using Magnetic Resonance Imaging

Efficient processing of fibrous biomass requires adequate rheological characterization of fiber suspensions. Most published data on biomass rheology has been obtained using rotational rheometers and interpreted through generalized-Newtonian models. Due to the large size of biomass particles, fast settling, entanglements and migration occur. These phenomena cause difficulties in rheological studies made with rotational rheometers and analyzed via generalized-Newtonian models. Direct imaging of velocity profiles provides a way of characterizing flow in the presence of such non-idealities. We used magnetic resonance imaging to measure velocity profiles of cellulosic fiber suspensions flowing in an horizontal tube. Pressure drop and video images were simultaneously recorded. We observed a strong influence of fiber length, concentrations and flow rates on velocity profiles and pressure drops. At low flow rates and low concentrations vertically asymmetric velocity profiles were observed due to settling. At increased concentrations, entanglement of longer fibers was detected as solid-like regions moving with uniform velocity. Disruption of fiber entanglements at higher flow rates was observed in some cases. Advantages and challenges of using MRI for rheological characterization of biomass suspensions having various particle sizes are discussed.