Abstract
Twin screw extruders are commonly used in polymer processing. Key design features of these devices are the kneading blocks, which are designed and arranged such that e.g., additives and fillers are efficiently distributed in the polymer melt. This work presents CFD analysis of bubble breakup in these kneading zones, comparing counterrotating to corotating systems using both 2D and 3D analyses. The Level Set method is used to model a multiphase system of dispersed supercritical CO2 bubbles in a polypropylene phase. Droplets with radii of 0.5 mm are initialized close to the zone in between the kneading blocks. The results show that the bubble breakup phenomena differ in counter and corotating systems due to different flow profiles. In both cases the breakup shapes are predominantly driven by flow characteristics with counterrotating configurations showing stronger elongation of the bubbles due to elongational flow sections close to the initialization of the original bubble, leading to pinch-off of smaller bubbles compared to the corotating cases.
