A BOUNDARY-ELEMENT ANALYSIS OF PLANAR DROP DEFORMATION IN THE SCREW CHANNEL OF A MIXING EXTRUDER

The influence of shear and elongation on the planar deformation of a d rop is examined as it is driven by the ambient flow in the screw chann el of a continuous mixer. Viscoelastic fluids are considered, and a bo undary-only formulation is implemented. The effects of viscosity, elas ticity and initial position of the drop on the motion of the drop are investigated. It is found that the drop may or may not always deform i ndefinitely as it is subjected to the shear flow induced by the relati ve movement of the barrel. Indeed, it is shown that if the drop is pla ced close to the entrance, it tends to get entrained towards the core region between two flights no matter how close to the barrel is its in itial location. If, on the other hand, the drop is initially placed fa r from the entrance (but always close to the barrel), shear effects te nd to be dominant enough for the drop to undergo almost rigid-body rot ation. (C) 1998 Elsevier Science Ltd. All rights reserved.