Selected Topics of Modeling Transport Phenomena in Single-Screw Extrusion Viscous Dissipation, Melt Conveying, and Mixing
Sprache des Titels:
Englisch
Original Kurzfassung:
Single-screw extruders are among the most important processing machineries in the polymer
industry. They are used in continuous production lines of semi-finished products (e.g., films, sheets,
pipes, profiles, and fibers) and in recycling extrusion lines. Additionally, single-screw extruders are
used as plasticizing unit in injection- and blow-molding machines. As a result of the economic
challenges, polymer processing companies are forced to run the processing units with increased
throughput. Nevertheless, the required melt quality must be guaranteed. In order to meet the
increased requirements on the processing machinery an improved understanding of the extrusion
process, physical processes, and transport phenomena is needed.
The main goal of this work is the development of improved, novel, innovative, and enhanced
models for describing and modeling functional processes of single-screw extrusion for scientific and
industrial use. The focus in model development lies not only on accuracy, but also on numerical
stability for application in digital twins and model-based predictive control. Additionally innovative
and novel concepts are investigated that deepen and extend the understanding of screw extrusion
in theory and practice. This thesis deals with modeling transport phenomena with special
consideration of viscous dissipation which is mainly responsible for the melt temperature
development. Additionally melt-conveying and pumping, as well as mixing, are investigated.
The main focus of this thesis is related to analyzing the viscous dissipation of polymer melt flows in
single-screw extruders, and the development of universal symbolic regression models that
accurately predict viscous dissipation. Viscous dissipation models are developed for a one-, two-,
and three-dimensional modeling framework. The non-Newtonian flow behavior is considered by the
power-law model. By applying the theory of similarity the characteristic dimensionless influencing
parameters are derived. Based on these independent influencing parameters, comprehensive sets
of design points have been generated and its flow equations have been solved numerically.
Approximation models for viscous dissipation have been developed based on the numerically
derived results by applying symbolic regression based on genetic programming. Models are
presented for both given pressure gradient and given throughput rate. These developed models
allow fast, stable, and accurate prediction of viscous dissipation for pressure-generating and
pressure-consuming (overridden) melt-conveying zones without the need of further time-consuming
and computationally expensive numerical simulations. Additionally extended regression models for
predicting the pumping capability of two- and three-dimensional flows in single-screw extrusion are developed.
The one-, two-, and three-dimensional models predicting viscous dissipation and pumping capability are based on the flat-plate model. This widely accepted modeling approach does not consider the influence of the channel curvature. As part of this thesis, the effect of the channel
curvature on flow rate and viscous dissipation is investigated for a two-dimensional power-law flow in metering channels. The obtained results allow estimating the application limits for the flat-plate
model.
Forschungs-