Non‐Newtonian Fluid Mixing in a Twin‐Screw Mixer Geometry: Three‐Dimensional Mesh Development, Effect of Fluid Model and Operating Conditions

Abstract

Mixing was examined in a Readco continuous mixer (Readco Kurimoto, LLC, York, PA); a mesh was developed for three‐dimensional (3D) finite element method simulation and validated against experimental Newtonian fluid results. The mesh was designed to ensure accuracy in areas with a high velocity gradient while minimizing computational cost. It was utilized for investigation of non‐Newtonian fluids, including power‐law and Bird–Carreau models. Simple shear flow is seen at high in the center of the mixer; efficient dispersive mixing appears near the barrel wall at all flow rates. Both configurations experience increasing velocity and with mixer speed. Efficient dispersive mixing is observed near the barrel center with parallel paddles. Staggered paddles cause areas of backflow, improving fluid retention time. Under the same operating conditions, the Bird–Carreau fluid shows the greater influence of paddle motion, including less flow‐through and significant backflow. Maximum is higher than that seen for the power‐law fluid, while mixing index maxima are similar for both fluids.

This work evaluates mixing using complex fluids in a realistic geometry and explores the effect of different operating conditions. Previous work has been confined to mainly Newtonian fluids or simplified geometries. A major benefit of 3D numerical simulation is that it enables comprehensive, noninvasive fluid analysis and determination of mixing quality. The most valuable simulations are those that closely mimic existing equipment scenarios. This information will allow industry users to design more efficient mixers and develop better mixer configurations with lower capital cost. This is particularly important to the dough industry which needs a well‐defined mixing profile for both product rheology and machinability.