AERODYNAMICS IN THE BLOWN FILM PROCESS

Most industrial and laboratory blown film lines use an air ring with one or more lips to produce an annular air jet that cools the polymer extrudate. Experience in operating blown film lines indicates that the air flow around the bubble plays an important role in both heat transfer and momentum transfer. The former has received some attention in the literature, but few investigations have been made on the latter. This paper deals with the aerodynamic aspect of the blown film process. An air flow field similar to that in the blown film process was produced by blowing air past a rigid model. Aerodynamic experiments were carried out to determine the velocity and pressure distributions, and the overall axial force on the rigid model. Theoretical predictions using the techniques of superposition of stream functions and macro-balances of mass and energy were compared with experimental data.