Yuzhen Jin

An investigation on the distribution of massive fiber granules in rotor spinning units

Rotor spinning is an open-end spinning method that uses air as the medium to transform the fibers into yarn. Nowadays, the properties of its final product—yarn—such as yarn strength and yarn twist, are not satisfied due to the fiber morphology, which greatly depends on the distribution of the massive fibers in the rotor spinning unit (RSU). In this paper, theoretical analysis is given to describe the trajectory of fiber on the slide wall. A numerical study is performed with the massive fibers being simplified into granules to study their distribution characteristics in the RSU. According to our numerical results, the forming process of the fibrous ring is discussed and the effects of two variables, the rotor speed and the angle of the slide wall, on the distribution of fiber granules were also studied. The simulation results indicate that the fiber granules are not evenly distributed during their transport in the fiber transport channel (FTC) and they tend to accumulate on the upper and lower edge of the FTC. The distribution of fiber granules in the groove (fibrous rings) is closely related to the rotor speed. The higher the rotor speed, the longer and thinner the fibrous ring. The distribution of fiber granules on the slide wall is related to the angle of the slide wall such that a smaller angle leads to a scattered distribution on the slide wall, while a larger angle tends to bring a concentrated one. The simulation results show good agreements with our experimental results.

Characteristics of intersecting airflows in the narrow flow channel

Abstract Air-jet loom is a kind of shuttleless loom, which is widely used in textile industries. The weft insertion system is composed of main nozzle, auxiliary nozzles, and profiled dent groove. The jets from the main and auxiliary nozzles intersect in the profiled dent groove. The velocity and stability of the intersecting airflows have a direct impact on the yarn’s motion. In this paper, the commercial software is adopted to simulate the intersecting airflows in the profiled dent groove. The result shows it is reasonable that the distance from the main nozzle to the first dent is 15 mm. The optimal distance from the main nozzle to the first auxiliary nozzle is between 45 and 50 mm based on the criteria of the utilization efficiency of the airflow. According to the standard of airflow stability, when the spray angle of auxiliary nozzle is about 7°, the standard deviation of the radical airflow velocity is the smallest in different cross sections. Therefore, the intersecting airflows are the most stable when the spray angle of auxiliary nozzle is about 7°. The velocity distribution of intersecting airflows in the profiled dent groove is measured using Particle Image Velocimetry (PIV) technique. The research results can provide some useful references for the optimization of the weft insertion system of the air-jet loom.

An investigation of some parameter effects on the internal flow characteristics in the main nozzle

The air-jet loom is widely used in the textile industry and the main nozzle is one of its key components. In this paper, the influence of some parameters, including the input air pressure and the structure of nozzle core and its internal diameter, on the internal flow field of the main nozzle is analyzed. Then the optimized structure of the main nozzle is proposed from the perspective of fluid dynamics. In the present simulations, the realizable k - ɛ model is applied to model the internal flow field of the main nozzle. The results show that the velocity in the annular throat reaches supersonic. Moreover, the pressure at the end of the nozzle core is the lowest in the main nozzle. It is also shown that the input air pressure has little effect on the axis velocity in Zone B, but on the other hand, has a great influence on the near-wall velocity field and the axis velocity in Zone C. In addition, an optimized structure of the nozzle core is proposed in this paper. It is found that with the proposed structure, the velocity boundary layer near the wall of Zone B in the accelerating tube can be well improved, and rapid diffusion of airflow in this area can be avoided. These help increase the moving speed of the weft yarn. Last but not least, we also show that decreasing of the internal diameter of the nozzle core improves the axis velocity of the weft accelerating tube. However, it brings a stronger turbulence at the same time.