Analyzing the flow characteristics of co-rotating twin-screw extruder conveying elements

Modeling of the transport phenomena in fully intermeshing co-rotating twin-screw extruders is key to predicting their processing characteristics, and is commonly based on significant geometric simplifications, such as the flat-plate approximation, and ignoring flow in the clearances. In this work, we analyzed the conveying characteristics and power consumption of double-flighted fully intermeshing co-rotating twin-screw extruders, taking into account the full three dimensional geometry. First, we transformed the problem into a dimensionless representation and identified its characteristic influencing and target parameters by applying the Buckingham Π-Theorem. We then analyzed the fundamental relationships between flow rate, pressure gradient and power requirement, defining suitable conveying and power parameters for a Newtonian fluid. Based on these findings, a comprehensive numerically driven parametric design study was conducted. For each individual modeling setup, the flow field was predicted by means of a full three-dimensional FEM analysis, which was then used to compute the conveying and power parameters. The numerical results include the effects of screw and nip clearances and thus enable assessment of the influence of wear on processing behavior. Additionally, by combining the results of the conveying and power parameters, the viscous dissipation rate and thus the melt temperature increase can be estimated.