Comparative computational analysis of dispersive mixing in extension-dominated mixers for single-screw extruders

Enhanced dispersive mixing can be achieved by harnessing extension-dominated flows, because they are more efficient in agglomerate/droplet breakup than shear-dominated flows. Herein, we compare computationally the performance of two single-screw extrusion mixing sections with significant extensional flow components, the Chris Rauwendaal dispersive (CRD) mixer and the extensional mixing element (EME), recently proposed by the authors. Tapered slots in the CRD and hyperbolic contractions in the EME attempt to create extensional stresses through significant velocity gradients. Our studies confirm that EMEs are a better dispersive mixer than the CRD mixer, as they impose more intense and uniformly distributed extensional flow in a higher volume fraction of the material, and with less specific mechanical energy consumption. Overall, the EME design with a biaxial contraction was found to be the best dispersive mixer for single-screw extruders (SSE). The manuscript also summarizes all the existing dispersive mixers for SSE and ranks them relatively for their dispersive mixing capability.