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

Abstract

In this work, coextrusion experiments utilizing an industrial 9-layer Brampton Engineering coextrusion film blowing line for LDPE/LDPE/tie/PA6/EVOH/PA6/tie/LDPE/LDPE film production has been performed in order to investigate the effect of cooling intensity on the bubble shape, temperature profile and final mechanical properties of the produced multilayer film. Obtained experimental, data followed by theoretical parametric analysis were used to evaluate three different convective heat transfer models by using simple variational principle based film blowing model. For the studied processing conditions and given multilayer structure of the coextruded film, it has been demonstrated experimentally that reduction in the heat transfer coefficient leads to increase in Young's modulus and yield strength. Secondly, it has been found that the variational principle based model can describe measured multilayer bubble shape reasonably well and finally, the Muslet & Kamal heat transfer model (Muslet and Kamal, 2004) provides more realistic behavior than Campbell heat transfer model (Campbell, 2014) or Constant heat transfer coefficient model, especially if the bubble has very high freezeline height. (C) 2015 Elsevier Ltd. All rights reserved.