Abstract:

Objective Vortex spinning has been developed rapidly in recent years due to its unique advantages. However, the issue of excessive energy consumption of the vortex spinning nozzle is still unresolved. In order to reduce the energy consumption during the vortex spinning process without significantly influence the yarn strength, this study investigates the effect of the nozzle pressure (P) and the number of the injectors (N) on the air consumption of the nozzle and the strength of vortex spun yarn.

Method The computational fluid dynamics (CFD) method was adopted to simulate the airflow characteristics inside the nozzle. The air consumption and the yarn tenacity were predicted based on the static pressure and mechanical energy of the airflow. The air flow rate and yarn strength were experimentally measured to verify the numerical results.

Result Due to the pressure difference between the nozzle inlet and the vortex chamber, the mechanical energy of the airflow slightly increased in the fiber guiding passage. The mechanical energy of the airflow reached its maximum value in the region around the spindle tip with the influence of the air-jet. Then the mechanical energy of the airflow exhibited a decreasing trend in the annular region between the spindle and the vortex tube along the positive Z-axis. With the increase of nozzle pressure from 0.4 MPa to 0.6 MPa, the static pressure in the vortex chamber and the annular region between the spindle and the vortex tube generally showed a decreasing trend, as the static pressure at the injector exits was increases. The pressure difference between the air reservoir and the injector exits was further increased along with the increase of the nozzle pressure, resulting in the increase of air consumption. The mechanical energy of the airflow in the vortex chamber was slightly increased with the increase of the nozzle pressure, resulting in an increased efficiency of fiber separation. The mechanical energy of the airflow was increased significantly in the annular region between the spindle and the vortex tube, resulting in an initial increase followed by a decrease in the twisting efficiency. With the increase of the number of injectors, the static pressure was first decreased and then increased in the vortex chamber, while the pressure in the annular region between the spindle and the vortex tube was decreased. There was negligible variation in the static pressure at the injector exits, this gaving an insignificant difference in the flow rate through a single injector. The mechanical energy of the airflow in the vortex chamber was first increased and then decreased with the increase of the number of injectors, while the mechanical energy of the airflow in the annular region between the spindle and the vortex tube was increased monotonously. It is crear that either an excessive or an insufficient number of injectors was favorable for fiber separation and twist insertion. The experimental measurements showed that the flow rate of the airflow entering the nozzle exhibiteds an increasing trend as P increases, while the yarn tenacity was initially increased and then decreased. With the increase of N, the flow rate of the airflow entering the nozzle tended to be directly proportional to the number of injectors, while the yarn tenacity was first increased followed by a decrease.

Conclusion The mechanical energy of the airflow is low in the vortex chamber and the yarn passage, while was relatively high in the annular region between the vortex tube and the spindle. With the nozzle pressure was increased from 0.4 MPa to 0.6 MPa. It was found that the air consumption of the nozzle is positively related to the number of injectors. The prediction of air consumption is generally consistent with the experimental measurement of the flow rate. The mechanical energy of the airflow in the nozzle was increased as P increases, and as N increases, the mechanical energy of the airflow in the vortex chamber initially is increases and then decreases. The prediction of yarn strength is consistent with the experimental measurements. Overall, considering the requirement for yarn tenacity, the air consumption of the nozzle is the minimum when P=0.45 MPa and N=4.

Key words: vortex spinning, nozzle, flow field, mechanical energy, air consumption, numerical simulation