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 drop is examined as it is driven by the ambient flow in the screw channel of a continuous mixer. Viscoelastic fluids are considered, and a boundary-only formulation is implemented. The effects of viscosity, elasticity 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 indefinitely as it is subjected to the shear flow induced by the relative movement of the barrel. Indeed, it is shown that if the drop is placed 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 initial location. If, on the other hand, the drop is initially placed far from the entrance (but always close to the barrel), shear effects tend to be dominant enough for the drop to undergo almost rigid-body rotation. (C) 1998 Elsevier Science Ltd. All rights reserved.