A Basic Model for a Twin-Screw Extruder

A model based on solving thermal balance and Stokes equation in a corotating twin-screw extruder with deep screw channels was developed. The present stage of the model described the evolution of temperature in the conveying section and the isothermal evolution of pressure in the melt pumping and reverse screw elements, with a Newtonian viscosity adapted to each part of the screw; residence time distribution in the whole extruder was also computed. Experimental validation was carried out on a pilot scale twin-screw extruder CLEXTRAL BC 45 fed with maize starch. Good agreement was found between the theoretical and actual temperature and pressure profiles, as well as with residence time distribution. In standard operating conditions (30 kg/hr, 200 rpm), the pressure generation in one C-shaped chamber was computed to be about 2.2 MPa, while pressure drops were about 0.3 MPa (intermeshing zone) and 0.5 MPa (reverse screw element) while the major part of the residence time per unit of screw length was spent in the reverse screw element.