Flow characterization in cylinders for pneumatic spinning

Traditional spinning systems are reaching profitability limits due to high production costs and low productivity. Pneumatic spinning is seen as a developing system; its productivity is much higher than that achieved by conventional systems. This paper evaluates one of the main factors that prevents an increase of productivity in pneumatic spinning. This is the air currents generated at the drafting cylinder entrance, which interact with the incoming fibers, diverting them from their expected path. Using laser anemometry, the airflow velocity distribution around drafting cylinders has been measured and it has been found that vorticity is created at the cylinder entrance. Extensive CFD simulation on the airflow drag by the cylinders has given a clear inight into the vortex created, producing valuable information on how cylinder design affects the vorticity created. It has been found experimentally that the use of a drafting cylinder with holes in it produced good results, reducing the air currents and allowing a sharp increase in yarn quality, as well as an increase in productivity. A study of vortex kinematics has been undertaken, bringing a better understanding of vortex creation, development, and breakdown.