Numerical investigation of non-Newtonian fluids in single screw extruders, Part II: Time-dependent studies

Abstract

Polymer processing techniques occupy nowadays a crucial role in the sustainable production of plastics/polymers, and polymer extrusion is in the center of these. This paper discusses the second part of a CFD study of a 3D single screw extruder, considering different transient aspects of the whole process, from the viscosity variation, residence time, to the chemical reactions taking place. The heat of reaction is included to incorporate the effect of these exothermic reactions, modifying in a coupled study the rheological properties, and hence the fluid behavior. The model incorporates mass, energy and momentum equations coupled with a non-Newtonian fluid model, where a shear-thinning/-thickening temperature-depending rheology correlation is modeled. The results show that the different physical phenomena cannot be solved separately but must be coupled in order to have practical results, since the reactions affect the heat transfer and this ultimately the rheological properties, affecting the flow parameters. Moreover, the transient analysis of the extruder (e.g. start-up) is vital in the proper design of the equipment and screw configuration.