A new approach to mixing enhancement in regular single screw extruder was presented with axial reciprocating motion of barrier to generate chaotic mixing.Such a model with the barrier lower than the screw channel was proposed and the corresponding mathematical model was developed.The periodic flow and mixing performance of Newtonian fluid in such an extruder were numerically simulated.The finite volume method was used and flow domain was meshed by staggered grids with the periodic boundary conditions of the barrier motion being imposed by mesh supposition.Fluid particles tracking was carried out by the fourth order Runge-Kutta scheme.Distributive mixing was visualized by the evolution of passive tracer initially located in different positions.The growth of interface stretch of the tracers with time and cumulative residence time distribution (RTD)were also obtained.The Poincaré section was used to reveal the geometrical scale of chaotic mixing

and the results confirmed that the axial reciprocating motion of the barrier could lead to chaotic mixing to enhance mixing performance.The new approach could make the broadening of RTD much narrower than that in fixed barrier geometry along with the much smaller mean residence time.In contrast

the mixing performance in the conventional single extruder with a fixed barrier was also investigated.