VELOCITY-FIELD IN A TWIN-SCREW EXTRUDER

Velocity measurements inside the screw channels of a co-rotating, self -wiping, twin-screw extruder were carried out. A laser Doppler anemome ter (LDA) system was used to measure tangential and axial velocity com ponents in the translational region of one of the screws of a twin-scr ew extruder. The velocity measurements were carried out using heavy co rn syrup at different screw speeds and for two forwards conveying elem ents differing in their pitch. It was found that velocity profiles ir: the translational region were substantially affected by the pitch of the screw element, however, screw speed (30-90 r.p.m.) did not have a significant effect on the shape of the velocity profiles. The range of velocity values in a 14 mm pitch screw element was wider than that in a 28 mm pitch screw element. Experimentally measured velocity profile s were compared with predictions of a one-dimensional model, which sho wed that the model underpredicted the velocity values, for the 14 mm p itch element.