Abstract:

Spinning is a process in which polymers are extruded in a certain form to form chemical fibers, which are then processed to make textiles commonly used in daily life. In the process of melt spinning, it is usually necessary to add functional granules into the melted polymer melt, and use a static mixer to improve the mixing effect between the melt quality and dispersed phase particles, so as to prepare functional fiber materials. However, in the actual production process, the dispersion mixing of functional particulate matter is always a difficult problem, particulate matter tends to agglomerate within the polymer melt, and the measurement process of the experiment is complex. Therefore, improving the spinnability of the polymer melt during the spinning process and reducing the agglomeration of particles within the fiber can effectively improve the functionality of the fiber material. In order to solve the problem of melt quality degradation and mixing performance deterioration caused by online particle addition during melt spinning, the finite element method (FEM) was used to model the geometry, mesh, set material parameters and boundary conditions, and calculate the solution for static mixers with different structures and process parameters, and the post processing results and the pressure drop curve in the flow direction were obtained. Meanwhile, in order to quantitatively characterize its mixing performance, the tracer particle technique was used for analysis, and the cumulative probability functions of separation scale, residence time distribution, and maximum shear stress were obtained by solving the fourthorder RungeKutta algorithm, and they were statistically analyzed. The analysis results show that when the aspect ratio is increased from 1 to 1.75, the pressure drop in the pipe rises from 0.52 MPa to 0.62 Mpa, the flow resistance increases, the decreasing speed of the separation scale becomes smaller, but the difference at the outlet is not significant, the peak of residence time gradually decreases, the axial mixing effect is better, the probability of the maximum shear stress greater than 5 kPa is raised to 78%, and the degree of agglomeration of the dispersed phase is reduced. The inlet flow rate is increased from 2×10-5 m3s to 8×10 -5 m3 s, the pressure drop of the melt increases from 0.52 MPa to 2.00 MPa, the flow resistance increases, the separation scale changes little, the peak of the residence time becomes higher, the axial mixing effect is worse, the probability of the maximum shear stress greater than 10 kPa reaches 83%, and the degree of agglomeration of the dispersed phase decreases. The innovation is reflected in the use of finite element method instead of experimental process, which significantly reduces the measurement difficulties and human errors due to the complexity of the experiment, reduces its cost and cycle, and can play a guiding role in the actual production process.

Key words: kenics static mixer, melt spinning, finite element method (FEM), tracer particle technology, aspect ratio, inlet flow rate, max shear stress

摘要： 为了解决熔体纺丝过程中由于在线添加颗粒引起的熔体品质降低与混合性能变差的问题，采用有限元法针对不同结构与工艺参数的静态混合器进行了建模与求解，得到了后处理结果。同时，为了定量表征其混合性能，采用示踪粒子技术求解了分离尺度、停留时间分布以及最大剪切应力的累积概率函数并对其进行统计学分析。结果表明：长径比由1升高到1.75时，管道内压力降由0.52 MPa上升至0.62 MPa，分离尺度差异不大，停留时间峰值逐渐减小，最大剪切应力大于5 kPa的概率提升到78%。进口流量从2×10-5m3s提升到8×10-5 m3s，熔体的压力降从0.52 MPa上升至2.00 MPa，分离尺度变化较小，停留时间的峰值变高，最大剪切应力大于10 kPa的概率达到83%。

关键词: 静态混合器, 熔体纺丝, 有限元法, 示踪粒子技术, 长径比, 进口流量, 最剪切应力