Investigation of heat transfer in 9-layer film blowing process by using variational principles

Abstract

Abstract. In this work, coextrusion experiments utilizing an industrial 9-layer Brampton Engineering coextrusion film blowing line has been performed under different processing conditions (low/high air cooling intensity) in order to evaluate variational principles based modeling approach using energy equation utilizing variable heat transfer coefficient along the multi-layer bubble. It has been revealed that the variational principle based model can describe the bubble shape and temperature profile reasonably well even if the multi-layer film has been viewed as the static elastic membrane characterized only by one material parameter -bubble compliance J, which was not allow to vary along the bubble. Moreover, it has been found that if the freezeline height becomes long, heat transfer coefficient starts to vary significantly along the bubble which has crucial impact on the temperature profile along the multi-layer bubble. The performed theoretical parametric study revealed that increase in blow-up ratio or decrease in bubble curvature and air temperature causing bubble cooling efficiency increases, which allows to cooled down the multi-layer bubble for the given freezeline height to solidification temperature by smaller amount of the air volume flow rate.

Blown film cooling numerical and experimental investigations

“…• Recently, due to the progress that occurred in the field of blown film production, the dependency of the bubble kinematics on the film surface temperature distribution and the temperature gradients inside the film thickness, some researchers devoted their efforts to combining the blown film aerodynamics with the bubble kinematics [6,[16][17][18][19]. Besides, the bubble's stability during the production process is also investigated as an important monitoring issue [20].…”