Analysis of Flow and Mixing in Screw Elements of Corotating Twin-Screw Extruders via SPH

Due to its meshless nature, the smoothed particle hydrodynamics method (SPH) provides high potential for the simulation
of free-surface flows and mixing in complex geometries. We used SPH to analyze the flow inside five typical screw
elements of corotating twin-screw extruders, two conveying elements, two kneading elements and a mixing element. Our
results show conveying capabilities, pressure generation and power input for various operation states, completely and
partially filled. We conducted a detailed mixing analysis based on tracer particles, which yielded the time evolution of
the intensity of segregation for different tracers. From that, we determined exponential mixing rates, which describe the
relative decrease of the intensity of segregation per screw revolution and characterize the mixing performance in different
operation states. This provides valuable input information for simplified models of extruders, which are relevant to
industrial applications and can significantly contribute to the efficient design, optimization and scale-up of extruders.