The major objective of our IFPRI project, which started in 1998, is to develop a comprehensive mathematical model of the extrusion process for “concentrated” dense suspensions using the Finite Element Method. The results of the numerical analysis need to be verified through experimental studies carried-out on industrial-scale and well-instrumented extruders. Other objectives include the development of various methods and apparati to probe the rheological behavior and microstructural characteristics of concentrated suspensions (“dense suspensions”) especially in the confines of the extrusion process. Single and twin screw extrusion processes (including co-rotating and counter-rotating twin screw extruders) and flow through dies are included in the scope of the project. The ability to determine the distributions of the pressure, stress, velocity and temperature which develop during the course of the extrusion process is the minimum information wherewithal necessary to understand the development of the structure and the ultimate properties of the processed suspensions. The project is carried out with massive support from other sources also including te US Army, Naval Surface Warfare Center and various corporations.
The major tasks of Year #2 were the modification of our FEM based source codes to accommodate the wall slip behavior of dense suspensions in 3-D, the initiation of the experimental studies of dense suspensions using a well-instrumented and industrial-size co-rotating twin screw extruder and the comparisons of the experimental and simulation results on various isolated sections of the twin screw extruder. The coupled flow occurring at a slit die and the exit section of the twin screw extruder was focused upon using a model suspension, which was well characterized. The experimental results (pressure and temperature distributions) agreed well with the results of our numerical simulation using 3-D FEM. During the next year we intend to expand our mathematical analysis to multiple sections of the extruder simultaneously on the single screw extruder, carry-out detailed experimental studies with realistic suspensions using again a well-instrumented single screw extruder with a complex shaping die and compare the experimental results with the numerical results.