Abstract: In the chemical fiber industry, the opening treatment of viscose or Lyocell staple fibers is an important process before the finished fiber. The fiber delivery tube,  one of the most important units of the post-treatment equipment, connects the cutting machine and the feed tank, and is used to transport the staple fiber cut off by the cutting machine and the flushing water. The viscose or Lyocell staple fiber cut by the breaker is fed to the feed tank, and the fiber is dispersed during the transportation process, so as to achieve uniform fiber laying of the feed tank, increase the washing effect of the refining machine, and improve the quality of the finished fiber. However, the traditional fiber delivery tube mainly plays the role of transportation, and the requirements for open fibers are not high. It is very important to explore the opening mechanism of bundle fibers and the influence of flow field state on fiber movement state to promote the rational design of fiber delivery tube structure and improve the opening effect of fibers.
In this paper, based on 3D modeling software and Cradle CFD numerical simulation software, the flow field model and fiber model in the fiber delivery tube were established to simulate the motion state of 2,000 fibers tow with length of 38 mm in the fiber delivery tube. The fluid inflow condition at the inlet of the fiber delivery tube was set as velocity inflow 1 m/s, and the outlet was set as static pressure outflow-natural outflow. The flow field was calculated by using steady state, pressure solver, RNG k-ε turbulence model and wall function method. The convection term was discrete by using second-order upwind scheme and was solved by using PISO algorithm based on SIMPLEC. Through the vector analysis of the pressure field, velocity field and flow field, and the analysis of the motion state of the fiber bundle in the fiber delivery tube, the influence of the flow field in the fiber delivery tube on the fiber movement was explored. The results show that when the fiber bundle enters the vertical pipe, it accelerates under the water flow and its own gravity. Due to the pressure gradient and velocity gradient in the pipeline flow field, the local velocity difference between the conveying process and the conveying fluid in the pipeline results in the opening effect of the fiber dislocation. The velocity of flushing water varies greatly at the bend of the fiber delivery tube, and the resulting velocity gradient is conducive to the opening of the fiber bundle. The flow field velocity gradient of the horizontal pipeline is small, and the speed change is relatively stable, so that the overall fiber is elongated and opened, which improves the fiber opening effect in the transportation process, and guarantees the continuously uniform output. The sudden increase in the diameter of the pipe leads to the vortex of the pipe, which hinders the forward transportation of the fiber. Therefore, for the design of the fiber delivery tube, the sudden increase in the diameter of the pipe tube should be avoided to reduce the phenomenon of fiber entanglement. In this paper, the results of the study describe the basic mechanism of the fiber bundle of opening, and reveal the fiber delivery tube flow field state influence on fiber transmission. Such results can provide reference for the design of the fiber delivery tube of chemical fibers and the textile industry.

Key words: fiber delivery tube, flow field model, Cradle CFD, fiber tow, opening , and loosening

摘要： 纤维输毛管的设计对粘胶纤维或Lyocell短纤维丝束的开松效果至关重要。为了探究纤维丝束在输毛管中的开松机理以及管道内流场状态对纤维运动状态的影响，采用三维建模软件建立输毛管流场模型，在商用软件Cradle CFD中建立纤维丝束模型结合流场进行耦合计算，研究分析了2000根长度为38 mm纤维丝束在输毛管中的运动过程。结果表明：纤维丝束在输毛管中受到流场作用的差异形成了纤维丝束运动的速度差，是纤维丝束开松的主要原因；输毛管的竖直圆形管道处存在较大的压力梯度，使纤维丝束整体受到压力差异，也为纤维开松创造条件；输毛管的锥型管位置处的速度场较复杂，有利于纤维丝束开松；管径的变化导致产生漩涡，阻碍了纤维的输送。研究结果可以为化纤与纺织行业输毛管设计提供参考。

关键词: 输毛管, 流场模型, Cradle CFD, 纤维丝束, 开松