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

  • Martin Robinson
  • Paul W. ClearyEmail author


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 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°) 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 is 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.


SPH Mixing Extrusion Screw Kneading FTLE 



The authors would like to thank Matt Sinnott for his assistance in constructing the CAD models of the extruder. Martin Robinson gratefully acknowledges research support from the EPSRC Cross-Disciplinary Interface Programme (EP/I017909/1).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Human and animal rights

This article does not contain any studies with human participants or animals performed by the author.

Informed consent

No individual participants were included in the study so there are no subjects for which informed consent requirements arise.


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Copyright information

© Crow 2018

Authors and Affiliations

  1. 1.Department of Computer ScienceUniversity of OxfordOxfordUK
  2. 2.CSIRO Data61Clayton SouthAustralia

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