啮合同向双螺杆挤出机普通螺纹元件末端共混物的混合形态 Ⅰ.物料三维流动路径的计算

Blend morphology of polymer at outlet of common screw element in an intermeshing co-rotating twin screw extruder Ⅰ.Computation of three-dimensional particle trajectories

用有限元方法对啮合同向双螺杆挤出机的螺纹元件流场进行了三维等温非牛顿模拟分析,根据流场分析所得到的速度场,通过编程计算得到了物料在啮合同向双螺杆挤出机螺纹元件中的三维流动路径。结果表明,由于存在着轴向回流,部分物料不能流出元件出口,而是从元件入口返流;物料在元件中的运动轨迹不尽相同,有的物料微元在整个流动过程中都围绕着2根螺杆以螺旋“∞”形向前运动,有的物料微元在流动过程中时而围绕1根螺杆连续旋转,时而围绕2根螺杆以螺旋“∞”形向前运动;在螺槽区,物料在螺槽的横截面内上下流动;回流物料微元数随着螺杆转速的增大、双螺杆挤出机产量的减小而增大。

Three-dimensional non-Newtonian isothermal flow fields of the common screw element were analyzed with establishing geometric models using the real geometry of barrel and screws.According to the velocity profile of flow fields, the three-dimensional particle trajectories in the screw elements were obtained by writing program.The results showed that some fluid particles could not flow out from the outlet of the screw element,but flow back to the inlet because of the existing of the backflow. The fluid particle trajectories were different: some fluid particles flowed around the two screw along the spiral path until it reached the outlet.Some fluid particles sometimes continued to flow forward around the same screw,sometimes flowed into the other screw channel when they flowing across nip region.There was up-down motion of the fluid particles when flowing across the screw channel region. The number of the back-flowing fluid particles increased when the rotation speed of the screw increased and the output of twin screw extruder decreased.