A Basic Study on Freezing of Food (Freezing Behavior of a Saline Solution Through a Semipermeable Membrane)

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It is well known that the freshness of food depends on the cooling rate in freezing food. Therefore, in order to control the freshness of food, it is important to obtain the effect of cooling rate on the cooling and freezing behaviors in cells. To do it, it is necessary not only to evaluate the processcs of flow, temperature and concentration distributions in a single cell, but also to consider the exchange of heat and mass inside and outside of cells through cell membrance.This study regards food as the cell aggregation. As a cell component, paying attention on free water having the characteristics of the highest freezing point in cell components, an aqueous sodium chloride solution (NaCl aqueous solution) with a concentration of 5% by mass was used. Furthemor, a micro porous film was used as a cell membrane taking account of function and strength.This study deals with the cooling and freezing behaviors of NaCl aqueous solution through a micro porous film from the viewpoint of thermal … More engineering. These behaviors were visualized and measured using a real-time laser holographic interferometry. For comparison, a copper plate and no partitions other than a micro porous film were used as partitions. Water other than NaCl aqueous solution was also used as liquid to be cooled.As a result, following conclusions were obtained.In the experiments using NaCl aqueous solution, there is no significant difference in the cooling process due to partitions. However, in the freezing process, NaCl rejected by solidification in the first cell goes into the second cell passing through a micro porous film with the progress of solidification. Therefore, it is necessary to consider mass transfer through films after solidification in analyzing food freezing.In the experiments using water, it is clarified that water itself passes through the micro porous film. However, there is little difference in heat transfer characteristics between the results using film and those using copper plate where water cannot pass completely. Less