Presentazioni e Articoli Tecnici

Single screw extrusion is a manufacturing method used to produce catalytic active extrudates. The understanding of the flow within the extruder is fundamental to optimise the shape of the screw to obtain a high quality extrudates. Due to the complex geometry of the screw and to the paste exhibiting a non-Newtonian behaviour, numerical simulations are fundamental to study of the system, hence the single screw extrusion was simulated in COMSOL Multiphysics®. Boundary conditions at both the inlet and the outlet were provided in terms of pressure. A no-slip boundary condition was assigned at the walls. Revolutions per time was specified for the rotating domain under the Moving Mesh interface. The rheology of the paste was implemented using the Herschel-Bulkley-Papanastasiou non-Newtonian model. The model was then validated in terms of flow rate of the paste. First, a Frozen Rotor stationary study was carried out, which provided a good estimate of the velocity flow field and pressure distribution into the domain under investigation. Results were then used as initial condition for a time dependent study to improve the convergence of the simulation and obtain a more accurate prediction of the flow field during the rotation of the screw. This model represents a tool to investigate the effect of the geometry of the screw on the flow and pressure fields. This is extremely valuable to optimise the geometry of the screw to improve the quality of the extrudate and reduce costly experimental trials.