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

Twin-screw extruders (TSEs) are known for their good mixing performance. Although global mixing per-formance has been the subject of many computational fluid dynamics studies, the actual mixing mech-anism 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 eval-uated LCS within a Smoothed Particle Hydrodynamics (SPH) framework and established that, unlike con-ventional 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 mix-ing and offer a novel viewpoint for geometry optimization.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Twin-screw extruders are known for their good mixing performance, but the actual mixing mechanism remains largely unexplored due to the complexity of the screw geometry. This study uses Lagrangian Coherent Structures to understand laminar mixing in various elements of twin-screw extruders and offers a novel viewpoint for geometry optimization.