Evaluation of Heat and Mass Transfers in Bi-Layer Films

4 Evaluation of Heat and Mass Transfers in Bi-Layer Films 

Two kinds of results are given separately those concerned with the heat transfer, expressed in terms of the temperature-time histories in various parts of the film and of the profiles of temperature developed through the thickness of the bi-layer film the other related to the transport of the contaminant by diffusion, expressed in terms of the profiles of concentration of this diffusing substance developed through the thickness of the film. 

Two bi-layer films whose layers have the same thickness are considered, with the total thickness for the film of 0.01 and 0.03 cm, respectively. 

Polyethylene terephthalate is chosen for the polymer - its thermal properties are found in the literature [11]. The values of the diffusivity at high temperature are not known yet, and some assumptions are made from the value at room temperature [12,13] (Table 3.2). 

For a film, the polymer sheath is moving with a rather high speed, leading to a forced heat convection between the sheath surface and the surrounding air. Thus heat is transferred either by forced convection at the film-air interface or by conduction through the thickness 

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