Detecting mixing barriers in Twin-Screw extruder elements via Lagrangian Coherent Structures

• Published in: Chemical engineering science Vol. 263; p. 118069
• Main Authors: Bauer, Hannes, Khinast, Johannes
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 14.12.2022
• Subjects: Lagrangian Coherent Structures; Laminar mixing; LCS; Smoothed particle hydrodynamics; SPH; TSE; Twin-screw extruder element; Laminar mixing; Smoothed particle hydrodynamics; TSE; Twin-screw extruder element; SPH; Lagrangian Coherent Structures; LCS
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2022.118069

[Display omitted] •A fully Lagrangian workflow to obtain Lagrangian Coherent Structures was implemented.•Transport barriers revealed the mixing mechanisms of twin-screw extruder elements.•Mixing barriers were determined and compared for various realistic screw geometries.•Tracer experiments show the link between of fluid element deformation and mixing barriers. Twin-screw extruders (TSEs) are known for their good mixing performance. Although global mixing performance has been the subject of many computational fluid dynamics studies, the actual mixing mechanism remains largely unexplored, probably due to the complexity of chaotic flow patterns caused by the complex screw geometry. In this work, we aim to understand laminar mixing in various twin-screw extruder elements via Lagrangian Coherent Structures (LCS). An LCS computation requires fluid element trajectories, which can be a limiting factor in 3D applications. Bypassing this potential problem, we evaluated LCS within a Smoothed Particle Hydrodynamics (SPH) framework and established that, unlike conventional methods, this methodology is efficient in complexly shaped deforming fluid domains. Mixing barriers in realistic conveying, kneading and mixing elements are computed, compared, and discussed. Repelling and attracting LCS reveal the stretching and folding events necessary for efficient laminar mixing and offer a novel viewpoint for geometry optimization.