Numerical investigation of non-newtonian fluids in single screw extruders, Part I: Steady-state studies

Polymer extrusion is considered one of the key processes in product processing nowadays, and its optimization is considered of the utmost importance in order to deliver proper products minimizing the use of resources. This paper presents the first part of a complete CFD study of a 3D single screw extruder model. In order to do so, mass and heat transfer coupled non-Newtonian fluid models are considered in a novel approach, where a shear-thinning/-thickening temperature-depending rheology correlation is modeled in COMSOL Multiphysics to reproduce the processing of polymer solutions. In this first part, a series of steady-state studies are presented, analyzing the system behavior and sensitivity to the different parameters involved but considering as well its dynamic behavior. Steady-state studies show that using only shear-thinning models underestimates crucial parameters such as pressure, viscosity and thermal profile due to differences in the velocity field and viscous stress tensor. Furthermore, the screw's influence in the heat transfer process cannot be considered negligible, since a recirculation circuit is created, which helps heating up the polymer entering into the barrel. This work provides important steps in further advances of 3D extrusion modeling processes by considering and evaluating more detailed physics and accurate boundary conditions.