Study On Fiber Motion In High Speed Airflow Within The Nozzle And Its Application

Air is being used in the processing of fibers into textile products. High speed air flow forms the basis of many new processes. But little has been done on the fundamental and theoretical study of air application in textile area. The thesis is to develop a better understanding into fiber/air interactions, and to guide the application of air in textile processes. To attain the purpose, the nozzle, which is widely used in textile machine, is studied.Numerical simulation is used to study fiber/air two-phase flow, and the Lagrangian approach is adopted because of its advantages in simulation. A number of assumptions are presented for simplification: (1) only the one-way coupling case is concerned ; (2) the action of turbulence pulsation to the fiber is neglected; (3) fiber/fiber and fiber/wall interactions are neglected; and (4) air flow is isentropic.The work of the thesis covers two parts. The first part is theoretical study, which is the emphasis of our work, including numerical simulation of high speed air flow in the nozzle, and the simulation of fiber motion in the air flow of the nozzle. The second part is the application of the theoretical study.According to the method to study fiber/air two-phase flow presented in Chapter 2, the motion of the air phase is calculated first. Therefore, in Chapter 3, numerical simulation of the air flow in the nozzle is performed, using finite volume method. The simulation resultsshow the flow characteristics in the nozzle, i.e. the distribution of velocity field and pressure field. The simulation results agree well with the previous work in LDA (laser Doppler anemometry) measurements, and verifies earlier researchers' speculative plausibility. The effects of parameters including nozzle pressure, jet orifice angle, jet orifice position and twisting chamber diameter on slow characteristics in the nozzle are studied. The simulation results show that the effects of nozzle pressure and jet orifice angle are significant, while jet orifice position has little influence on the distribution law of the velocity and pressure in the nozzle. Twisting chamber diameter influence the flow characteristics to a certain extent.In Chapter 4, by proposing a fiber model, the mathematical model of fiber/air two-phase flow is developed. On the basis of the numerical results of the air flow, the fiber motion in the nozzle is calculated. The images of the fiber motion in the nozzle are captured using high-speed photography. Results of experiments and simulation show considerable accordance. Meanwhile, the effects of nozzle and fiber parameters including nozzle pressure, jet orifice angle and fiber flexural rigidity on the fiber motion are studied. By introducing initial wrapping angle, the wrapping degree of the fiber is indicated quantitatively.The application of the theoretical study are focuses on the following three subjects: (1) the optimization of the parameters in air-jet spinning, such as nozzle pressure, jet orifice angle and fiber flexural rigidity; (2) predictions of the tenacity of air-jet spun yarns; (3) reducing yarn hairiness with JetRing and JetWind processes.In summary, as the fiber/air two-phase flow model is developed, the simulation of the fiber motion in the air flow within the nozzle is performed. Meanwhile, the characteristics of the high speed air flow in the nozzle are shown by numerical simulation. The study of the thesis develops a clearer understanding on fiber/air interactions, and provides new contentsto the area of air/particle two-phase flow.