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 ex perimental data, the results obtained from the numerical simulation of poly mer melt flow in the kneading disc section of an intermeshing co-rotating t win screw extruder. A quasi-steady state 3-D solution of the conservation e quations via the finite element method was obtained, and comparisons were m ade with experimental pressure profiles measured by McCullough and Hilton ( 1) on various kneading block elements. These measurements helped provide un derstanding of the flow patterns developed within the unit and provided a c omprehensive approach of validating the numerical model. Results confirm th e importance of a fully 3-D model for this type of geometry, where the mode l predicts the development of flow patterns in the radial directions and wi thin the intermeshing region. The influence of inlet and outlet boundary co nditions was studied and it was determined that they play an important role in the physical significance of the model solution. Comparisons of the sim ulation results with experimental data by McCullough and Hilton (1) for two different configurations of kneading discs showed good agreement, with som e differences in the peaks of pressure produced at the narrow clearances en countered in intermeshing co-rotating twin screw extruders. Differences bet ween simulation and experiments are attributed to a number of factors. It i s difficult to measure the very steep pressure gradients generated over sma ll lengths. The assumptions of isothermal flow and quasi-steady state may c ause an over-prediction of the pressure peaks. Simulation results describe the general trends and produce good quantitative agreement in most of the k neading disc region.