The liquid nitrogen quick freezing technique is to freeze the food by a large amount of latent heat and sensible heat absorbed by the liquid nitrogen food and the contact. The liquid nitrogen is ejected from the container and is abruptly changed to normal temperature and pressure, and the liquid state is converted into a gaseous state. During this phase change, the liquid nitrogen is boiled and evaporated into gaseous nitrogen at -195.8 °C, and the latent heat of evaporation is 199 kJ/kg; When the temperature rises to -20 °C under the normal pressure of °C, the sensible heat of 183.89 kJ/kg can be absorbed (the specific heat capacity is 1.05 kJ/(kg?K)), and the vaporization heat and sensible heat absorbed by the liquid nitrogen phase change process are absorbed. The heat can reach 383 kJ/kg [4, 6-8].
During the freezing process of the food, the food is rapidly cooled from the outside to the inside due to the large amount of heat taken away in an instant. Liquid nitrogen quick freezing technology uses liquid nitrogen as a cold source and has no harm to the environment. Compared with traditional mechanical refrigeration, it can achieve lower temperature, higher cooling rate, fast freezing speed of liquid nitrogen quick freezing technology, short time and freezing. The food is of good quality, high safety and no pollution. Therefore, liquid nitrogen quick freezing technology is a promising food cold processing technology.
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