On the Applicability of a Plug Flow Immersion Freezer: Theoretical Considerations

The most promising means of fast-freezing is the immersion of the product in a liquid of appropriately low temperature. The direct contact of a product with low temperature freezing mediums can, however, cause several problems, the most usual being the burning of its surface or even its rupture, due to the thermal shock it undergoes. It is possible to overcome these problems with the application of a plug flow immersion freezer. The aim of this paper is to investigate the applicability of a plug flow immersion freezer on a theoretical basis. For this purpose, a theoretical model was developed and tested for the freezing of squid. The results of this model indicate that the use of the proposed freezer is quite attractive for products of small thicknesses, up to 1 cm. A rather high value of the heat transfer coefficient can be achieved, while it is possible to set the temperature range of the freezing medium between -10 and -30°C, significantly higher than the ones found in most commercial freezers.