The effect of plastic film transmittance on heat transfer in a multilayer insulation structure of rectangular air cells for frozen food wrapping

As an alternative to a single-layer structure, a multi-layer structure of rectangular air cells was made of a transparent plastic film that aimed to enhance its thermal resistance. While multiplying layers, the authors observed only a slight growth of thermal resistance instead of the expected proportional increase. The purpose of the article is to investigate this phenomenon by means of a verified mathematical model of heat transfer, which was prepared for a multi-layer structure that respects radiation heat transfer throughout a number of parallel internal films. A model was used to investigate the film transmittance impact. Experimental freezing of a test package filled with Tylose gel showed that the use of insulation made of opaque film does not increase freezing time when compared to a transparent one. Experimental thawing showed that the application of wrap made of transparent film can increase package thawing time by about 1.6-2.2 times, and by about 1.8-3.7 times if the wrap is made of opaque film. (C) 2018 Elsevier Ltd and IIR. All rights reserved.