Hydrodynamics and mixing performance in a continuous miniature conical counter-rotating twin-screw extruder

The mixing performance in a miniature conical counter-rotating twin-screw extruder was investigated by means of experimental technique and computational fluid dynamics (CFD) simulation. An on-line experimental device based on the fluorescence detection was built to study the residence time distribution (RTD). Polypropylene was selected as the flow material and the blend of Polypropylene and anthracene was used as the tracer. This on-line detection device has good reproducibility. The hydrodynamics in the extruder was simulated by the finite element method (FEM) combined with the mesh superposition technique (MST). The particle tracking technique was carried out to evaluate the RTD and mixing efficiency. The effect of screw speed and feed rate on the hydrodynamics and mixing performance was investigated. The velocity magnitude and local shear rate tend to become smaller from inlet to outlet due to the decreasing diameters of screws. The mean length of stretch increases exponentially from inlet to outlet and the mean value of time averaged mixing efficiency remains positive along the axial direction.