Effect of geometry and fill level on the transport and mixing behaviour of a co-rotating twin screw extruder

Abstract

The transport and mixing properties of a co-rotating twin screw extruder with both screw elements and kneading blocks are explored using the Smoothed Particle Hydrodynamics (SPH) method. The use of a Lagrangian method enables simulation of extruders partially or fully filled with fluid and is not limited by problems associated with extreme mesh deformation due to the opposite rotation of the impellors or the small gaps between them.The cross-channel and axial fluid transport and mixing in the screw elements and kneading blocks are analysed. The effect of parametric variations in both impeller elements on the nature of the fluid flow and the mixing are explored; specifically the effects of varying the screw pitch (positively correlated to mixing rate), kneading block stagger angle (the mixing rate peaks at a block angle of 30 degrees) and gap size between the rotating elements (positively correlated to mixing rate). Flow and mixing behaviour is also investigated for partially filled cases, with a fill level of 50% producing the highest mixing rates for the screw elements. The presence of fluid free surfaces are shown as generally positive for mixing. We demonstrate significantly improved mixing when the orientation handedness of the screw and kneading blocks leads to concentration of fluid in the kneading elements.

Experimental Investigation and Numerical Simulation of a Self-Wiping Corotating Parallel Octa-Screw Extruder

“…Taki et al [ 18 ] found that the degree of fill was inversely proportional to the rotational speed and proportional to the feed rate. Robinson and Cleary [ 19 ] studied the effect of degree of fill on the transport and mixing behavior of a corotating TSE and found that a fill level of 50% produces the highest mixing rates for the screw elements. The degree of fill for the OSE was determined.…”

Developing HME-Based Drug Products Using Emerging Science: a Fast-Track Roadmap from Concept to Clinical Batch

“…Our approach uses smoothed particle hydrodynamics (SPH), a relatively new numerical method for simulating complex free surface flows occurring inside the rotating screws. SPH is a Lagrangian-based fluid dynamics model, with the fluid flow represented as a continuum of moving fluid parcels that can adjust naturally to the complex intermeshing movement of twin screw extruders without a numerical mesh (88)(89)(90)(91)(92)(93)(94)(95). The Lagrangian nature of the method also allows for a straightforward investigation of the flow in partially filled screw elements, as well as, a detailed investigation of the distributive mixing action of the screw geometry selected.…”

Boundary-conforming finite element methods for twin-screw extruders using spline-based parameterization techniques

“…Full 3D results have been obtained using commercial software like POLYFLOW which is based on a mesh superposition method that avoids re-meshing [3,4]. A rather recent development are methods using smoothed particle hydrodynamics [5,6]. These methods are extremely useful in case only partly filled extruders are considered.…”