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