Laval Tube Design of Yarn Suction Gun for Fully Drawn Yarn

Abstract

In order to demonstrate the effect of Laval tube structure of yarn suction gun on the yarn suction performance, throat diameter and throat length of the Laval tube were determined by theoretical analysis of the fluid field in the gun. 12 Laval tubes were designed, and yarn suction force (F) and mass flow rate of compressed air (G) were determined. Thereafter, yarn suction efficiency (η) was analyzed, where η=F/G. The rational geometrical parameters were obtained: converging angle of Laval tube α=90˚ and diverging angle of Laval tube β=6˚. The results indicated that there was a benefit to the airflow acceleration in the converging part of Laval tube and the formation of strong swirling flow by choosing the proper α, finally resulting in the improvement of η. The increase of super-sonic swirling airflow in the diverging section of Laval tube and the decrease of running resistance between the airflow and the yarn could be found when the reasonable β was selected, which also improved η. However, normal shock wave appeared in advance, the kinetic energy lost and the acceleration of airflow stopped due to the over-large β, leading to the decrease of η.