On the Interaction of an Air Jet with a Viscoelastic Tubular Film Produced during the Film Blowing Process

摘要

The effect of the air jet, which is used to increase the process stability and cool the polymeric film which is produced by the widely-used Film Blowing Process (FBP) is presented. The air jet is supplied circumferentially and tangentially on the outside surface of the tubular film that is pulled in the same upward direction. The two steady flow fields interact through the outside surface of the film which must be determined as part of the solution. Viscous, elastic, inertial, gravitational and interfacial forces are taken into account for the film, while only viscous and inertial forces determine the airflow. The film viscoelasticity is described using a variety of constitutive equations including the UCM and the affine exponential PPT models. The governing equations are simplified under the thin film approximation and a boundary layer formulation for the air. A similarity solution is obtained for the air jet and the air drag on the film is evaluated in terms of the bubble radius and introduced in the equations governing the film flow which are solved numerically by finite differences. It is found that the aerodynamic force on the film is very important in determining its shape, keeping it much closer to the vertical position for a longer distance from its extrusion level and, thus, stabilizing the process.