MECHANISMS OF MIXING IN SINGLE AND CO-ROTATING TWIN-SCREW EXTRUDERS

Previous experimental studies have revealed that the mixing efficienci es of widely used continuous processors such as the single and twin sc rew extruders depend on the types of screw elements, which are utilize d. It is generally recognized that the basic single screw extruder and the fully-flighted sections of the fully-intermeshing co-rotating twi n screw extruders are not efficient mixers, in contrast to the special ized mixing elements such as the kneading discs used in co-rotating tw in screw extruders. However, no simulation techniques were available t o characterize quantitatively and rigorously the mixing efficiencies o f continuous processors. In this study, we have solved the three-dimen sional equations of conservation of mass and momentum, and utilized va rious tools of dynamics to analyze the mixing occurring in single and co-rotating twin screw extruders. It is shown that simulation methods can indeed capture the relative differences in the mixing mechanisms o f continuous processors like the single and twin screw extruders. The ability to distinguish quantitatively between the distributive mixing capabilities of various continuous processors should facilitate numeri cal testing of new continuous mixer designs, optimization of operating conditions and geometries of existing mixers and the material-specifi c design of new mixers.