In situ quantitation of the index of mixing in a single-screw extruder by magnetic resonance imaging

Magnetic resonance imaging (MRI) has been used to quantitate in situ the goodness of laminar mixing of two streams of 1% aqueous sodium carboxymethylcellulose with different MnCl2 concentrations, flowing through a single-screw extruder (0.04 m diameter, length to diameter ratio of 4.575). Two-dimensional MR images (0.0002 x 0.0002 x 0.003 m 3 resolution) were acquired using gradient echo MRI protocols which had been calibrated to map MnCl2 concentrations. The resultant distributions were then used to calculate indices of mixing (normalized variances of concentration) in the part of the extruder under study. The smallest index (0.34) was measured near the outlet at the faster speed (30 rpm) and slower flow rate (47 ml min(-1)); and the largest index (0.73) was near the inlet for 20 rpm and 76 ml min(-1).