利用往复扰动螺棱强化单螺杆挤出机内混合模拟表征

Simulation of enhancement of mixing in single screw extruder by reciprocating barrier

提出了采用副螺棱轴向往复运动提高单螺杆挤出机混合的结构并建立了相应的数学模型。对挤出机内牛顿流体三维周期性流动和混合过程进行了数值模拟。采用有限体积方法,变量分布采用交错网格,副螺棱的周期性运动边界通过叠加网格方式实现。采用4阶Runge-Kutta方法实现流体追踪计算,得到了示踪剂界面增长及累积停留时间分布。采用Poincaré截面揭示混沌混合存在的区域,证实了副螺棱往复运动能够产生混沌混合效应提高螺槽内的混合效果,与其位置固定时相比,缩短了平均停留时间,停留时间分布变窄。作为对比,同时分析了常规的副螺棱位置固定的单螺杆挤出机内的相应混合行为。

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.