FLOW-FIELDS IN STRAIGHT AND TAPERED SCREW EXTRUDERS USING MAGNETIC-RESONANCE-IMAGING

Improving the fundamental knowledge of fluid transport in extrusion is essential for the improved control and design of extruder systems. In particular velocity profiles give valuable insight into residence time distributions and shear history which control final product characteristics. Due to the complicated geometry of extruders, mathematical models to predict flow behavior have been based on simplifying assumptions. Experimental verification of theory has proved to be a challenge due to the difficulty in obtaining complete flow profiles. This paper demonstrates the use of MRI to study flow in extruder geometries. Images of the velocity profile in both a straight screw and a tapered screw extruder have been generated using this non-invasive technique. Good agreement exists between experimental and theoretical velocity profiles for open and closed discharge for both straight and tapered screws.