Effects of the Polymer Fiber on the Flow Field from a Slot Melt Blowing Die

Exxon slot melt blowing dies consist of dual, rectangular, converging jets and are used in the industrial melt blowing process to attenuate molten polymer fibers. The air flow creates a drag force that accelerates the polymer and rapidly reduces the fiber diameter. For previous experimental and computational fluid dynamics studies, the effect of the fiber on the air was assumed to be negligible. By including the fiber as a boundary in the computational domain, this assumption was tested. A modified version of the Reynolds stress model was used to simulate the turbulent air flow field. It was determined that the centerline air velocity (located halfway between the fibers) has an increased maximum due to the presence of the fiber. In addition, the turbulence in the flow field is dampened by the presence of the fiber. The jet spreading rate is higher halfway between the fibers than at the center of the domain, where the fiber is located. The air flow around the fiber is nonuniform, leading to varied shear stress at different radial positions on the fiber edge. The temperature of the air flow is related to the ratio of the polymer to air flow rate; as this ratio increases, the hot fiber reduces the cooling rate of the air.