Numerical simulation of pressure and velocity profiles in kneading elements of a co-rotating twin screw extruder

The objective of this work is to validate, via comparison with available experimental data, the results obtained from the numerical simulation of polymer melt flow in the kneading disc section of an intermeshing co-rotating twin screw extruder. A quasi-steady state 3-D solution of the conservation equations via the finite element method was obtained, and comparisons were made with experimental pressure profiles measured by McCullough and Hilton (1) on various kneading block elements. These measurements helped provide understanding of the flow patterns developed within the unit and provided a comprehensive approach of validating the numerical model. Results confirm the importance of a fully 3-D model for this type of geometry, where the model predicts the development of flow patterns in the radial directions and within the intermeshing region. The influence of inlet and outlet boundary conditions was studied and it was determined that they play an important role in the physical significance of the model solution. Comparisons of the simulation results with experimental data by McCullough and Hilton (1) for two different configurations of kneading discs showed good agreement, with some differences in the peaks of pressure produced at the narrow clearances encountered in intermeshing co-rotating twin screw extruders. Differences between simulation and experiments are attributed to a number of factors. It is difficult to measure the very steep pressure gradients generated over small lengths. The assumptions of isothermal flow and quasi-steady state may cause an over-prediction of the pressure peaks. Simulation results describe the general trends and produce good quantitative agreement in most of the kneading disc region.