A NUMERICAL AND EXPERIMENTAL-STUDY OF 3-DIMENSIONAL TRANSPORT IN THE CHANNEL OF AN EXTRUDER FOR POLYMERIC MATERIALS

A numerical study of the three-dimensional flow and heat transfer in a single-screw extruder for polymeric materials such as plastics is car ried out. The mathematical model is considerably simplified by concept ually unwrapping the channel and fixing the coordinate system to the r otating screw. Despite this simplification, strong property variations , particularly in the viscosity, complicated cross-sections employed i n practical systems, large viscous dissipation effects and non-Newtoni an nature of typical extruded materials make the problem a very diffic ult one to model numerically. Therefore, the transport processes in th e extruder channel are simulated by means of a finite-element scheme w hich employs marching in the down-channel direction. The cross-section of the channel is taken as the commonly used rectangular or self-wipi ng profiles. An experimental study is also carried out using Newtonian and non-Newtonian fluids in order to provide data for the validation of the numerical model and also to quantify possible recirculation in the channel. Numerical results are presented on the temperature and ve locity fields, resulting shear effects, pressure rise, heat transfer r ates and viscous heating. The comparisons with experimental results in dicate good agreement. A strong recirculating flow is found to arise o ver the cross-section of the channel. It is shown that a three-dimensi onal modeling of the process is necessary to capture the effects of re circulation in the channel. However,the marching procedure considerabl y simplifies the model as well as the inclusion of property changes an d chemical reactions.