Study the effect of pressure on airflow field in vortex spinning nozzle by numerical simulation

Vortex spinning technology is with the help of high speed swirling airflow to twist fibers with open ends to form the yarn. Spinning parameters, such as nozzle pressure, has a great effect on yarn properties. In this study, different nozzle pressures were researched through spinning experiments, in addition, the homologous threedimensional computational fluid dynamics model of the nozzle was built to simulate the numerical calculation of the airflow in vortex spinning nozzle. Realizable k-epsilon model was used to simulate the turbulence of airflow in the nozzle. Unstructured tetrahedral grids which are suitable for airflow with wall effects and complicated boundary layers were adopted to divided grids in the computational area. The computational model of the airflow field was solved and the characteristics of airflow in vortex spinning nozzle was obtained. Through the results of numerical simulation, the corresponding airflow field within the nozzle was analyzed which provides reference for setting of spinning parameters. The numerical simulation results show that the velocity vector and the static pressure increase with the nozzle pressure, the principle of the swirling airflow is decided by the pressure distribution, a large negative pressure with appropriate axial and tangential velocity within the nozzle is conducive to the generation of the fibers with open ends and the twist. Spinning experiment results showed that the optimum nozzle pressure is 0.5-0.6Mpa, which shows a good agreement with the numerical simulation results. INTRODUCTION Vortex spinning is with the help of high speed rotating airflow in the vortex tube to twist fibers to form the yarn [1]. It’s a new spinning technology developed from air-jet spinning and improved in aspect of yarn property and flexibility of fiber materials [2]. High speed with short process, less hairiness, good resistance to pilling, better moisture absorption and release, and so on [3], are the prominent advantages of vortex spinning. Vortex spinning nozzle has a significant effect on the spinning processing and the yarn quality. Investigations have been carried out extensively and experimentally to study the characteristics in different types of swirling airflows to gain insight phenomena with the development of computer technology [4-9]. A reasonable agreement between CFD (computational fluid dynamics) predictions and experimental recorded flow characteristics were obtained in the studies of Sadiki A. and Wegner B. [10,11]. Oh et, al. [12] numerically studied the supersonic airflow within the main nozzle of the air jet loom. They derived the distribution of airflow pressure and velocity within the main nozzle and optimized the structure parameters of the nozzle. Rwei et, al. [13] numerically modeled the airflow field within the air texturing nozzle and analyzed the influence of parameters on air deformation of the nozzle. Zeng and Yu [14] obtained the characteristics of air flow within the first nozzle of air-jet spinning and studied the effect of airflow on fiber motion principle. Ulku [15] investigated experimentally the effect of some parameters on the structure and properties of vortex yarns. Computational fluid dynamics (CFD) software was used by many researchers [16-19] to simulate the three-dimensional numerical models for the airflow characteristics of vortex spinning nozzle, the stress field and the velocity field within the nozzle were obtained and analyzed in their studies. In this paper, three-dimensional computational fluid dynamics models were built to carry out the numerical simulation of the airflow in vortex spinning nozzle, spinning experiments were used to verify the simulation results. This study can provide a certain reference for setting up the nozzle pressure. Because the vortex yarn is usually hard, it is a compensation for the softness characteristics of viscose yarn, therefore, viscose fiber is widely used for vortex spinning, so this paper focuses the spinning parameters on viscose fiber. NOMENCLATURE ρ [kg/m] Air density v [m/s] Fluid velocity vector τ [-] Viscous stress tensor P [Mpa] Air pressure f [g] Gravity T [K] Temperature k [W/mK] Heat conductivity cp [J /kgK] Specific heat capacity ST [%] Viscosity dissipation rate 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics