(45f) 3D-1D Modelling of Twin-Screw Extruders

Twin-screw extruders (TSEs) are widely used for processing polymers, chemicals and foodstuff. The design of TSEs using experimental prototypes is expensive and time-consuming; hence, numerical simulations might substantially reduce costs and speed-up the development. Computational methods for the three-dimensional (3D) simulations of TSE include the Discrete Element Method (DEM) for the intake zone and the Computational Fluid Dynamics (CFD) method for the melting zone. To the authors’ knowledge, it is still not possible to apply a 3D method to the entire TSE due to the difficulties of simulating three-phase flows in partially-filled screw sections. These limitations may be overcome using one-dimensional (1D) models; however, the lower complexity is counterbalanced by a higher dependency on model parameters.

To combine the advantages of 3D and 1D methods, a new 3D-1D method is developed to simulate the polymeric extrusion in TSEs. The 3D part consists of DEM simulations of some representative volume elements (RVE), while the 1D part is a low-order model bridging the solution between the RVEs (Figure 1). The 3D simulations fully-resolve the granular flow in the RVEs to obtain torque, pressure and filling-level profiles for a certain operating condition, while the conveying elements are modelled using a lookup table approach connecting the 3D solutions of kneading and outlet elements. The lookup table is created prior to the 1D-3D simulation by performing in parallel a set of 3D simulations of the conveying element for different outlet counter pressures (Figure 2a-e). After the creation of the lookup table, the 3D-1D simulation starts from the last extruder element (RVE 4) and proceeds upwards, propagating the solution towards the inlet. The simulated pressure and filling-level profiles (Figure 3) agree qualitatively with the experimental results available in literature; a more quantitative comparison between numerical and experimental results will be presented at the Conference.