Abstract: A geometry in which the mixing of single screw extruder is enhanced by a reciprocating baffle is proposed and the effect of baffle amplitude on mixing in the screw channel is investigated. The corresponding physical and mathematical models are developed. The periodic flow and mixing of Newtonian fluid in such an extruder are investigated. Finite volume method is used and flow domain is meshed by staggered grids with the periodic boundary conditions of the baffle motion being imposed by the mesh supposition technique. Fluid particles tracking is carried out by fourth order Runge-Kutta scheme and the Poincaré section mappings are used in order to show the scale of chaotic mixing. The evolution of mixing patterns of the tracers and their growth of interface stretch with time are obtained which are released from different initial positions. The results reveal that the reciprocating motion of the baffle can lead to chaotic mixing region surrounded by the pseudo-periodic regions with two KAM tubes inside. The tracers will experience the exponent growth with time when captured by the chaotic mixing zones with the linear growth when trapped in the pseudo-periodic zones. The larger the baffle amplitude is, the smaller the inner pseudo-periodic region is, the larger the chaotic mixing region is.

Key words: Chaotic mixing, Finite volume method, Front tracking, Poincaré section, Single screw extruder