A numerical investigation of external cooling on a blown film

Abstract

Blown film has a wide range of applications from grocery and shopping bags to fresh food wrap and scientific balloons. Commercial blown film production is often limited by the rate of cooling that can be achieved in the production line. During the blown film processing, the extrude is in the form of a bubble freely extruded vertically upward. In this study, the thermal and flow field behaviors have been numerically investigated due to external cooling of Linear Low Density Poly Ethylene LLDPE film with a single lip air ring using a commercial CFD simulator. The thermal behavior and flow field have been determined from the solution of the partial differential equations for the conservation of mass, momentum, and energy, in addition to modeling the melting and solidification of the moving blown film. The film production is limited by the cooling rate that can be achieved through the air ring. The results indicated that, the film surface temperature distribution, heat transfer coefficient are mainly influenced by the external cooling air inlet conditions, blown film flow rate and air ring design. The enhancement on heat transfer coefficient has been achieved by increasing the external cooling air flow rate. Moreover, small modification of single lip air ring affects the velocity distribution around the bubble surface, hence affects the heat transfer coefficient. Moreover, the elimination of Coanda effect was investigated by adding an additional air supply through the lower part of the air ring.