(297a) Using Computational Fluid Dynamics to Study Effects of Fiber on the Air Flow from an Annular Melt Blowing Die

Annular air jets are used commercially to attenuate a polymer fiber in the melt blowing process. As polymer is extruded from a small capillary, the air flow from the jet creates a drag force on the surface of the polymer. The result is a rapid attenuation of the polymer into a fine fiber. Many experimental and computational studies of the air flow in the melt blowing processes neglect the effect of the polymer fiber on this flow. In the present work, computational fluid dynamics (CFD) was used to examine the effect of an axial moving polymer fiber on the air flow field from an annular jet, which is a common configuration for melt blowing dies. The turbulence in the air flow was simulated using a modification of the Reynolds stress model. The presence of the fiber alters the air flow field close to the fiber surface. In addition, the presence of the polymer leads to an increase of the jet spreading rate. As the inlet air flow rate was decreased, relative to the polymer flow rate, the effect of the polymer on the air flow field was observed to become stronger. The entrainment coefficient, which is a good indicator in measuring changes in the overall flow field, was not significantly changed by the presence of the fiber. Another important finding is that the polymer fiber has a dampening effect on the turbulence. In fact, the presence of the polymer filament actually improves the air flow field for the melt blowing process.