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Principle of Vacuum Freeze Dryer

The freeze-drying machine is a kind of low-temperature drying equipment that uses the principle of sublimation to dehydrate materials, also known as a vacuum freeze dryer. The principle of the freeze dryer is to freeze the water-containing material into a solid, and use the sublimation performance of water under low temperature and low pressure conditions to dehydrate the material at a low temperature as a new drying method. The product obtained by vacuum freeze drying is called a freeze-dried product.
The vacuum freeze dryer is suitable for the drying of high-end active pharmaceutical ingredients, Chinese herbal medicines, biological, wild vegetables, dehydrated vegetables, food, fruits, chemicals, pharmaceutical intermediates and other materials. Freeze vacuum drying is a new type of cabinet structure introduced by the vacuum freeze dryer that combines the refrigeration system, vacuum system, heat transfer oil heating system, and moisture removal system. It makes use of the material storage space in the cabinet for drying.
To put it simply, the principle of the freeze dryer is to place the sample in a vacuum environment so that the free water in the sample is volatilized through the change from high temperature to low temperature, and the bound water in the sample cannot be volatilized. The purpose is to achieve longer storage time of samples.
Water has three phases: solid, liquid, and gas. According to the phase equilibrium theory in thermodynamics, as the pressure decreases, the freezing point of water does not change much, but the boiling point gets lower and lower, approaching the freezing point. When the pressure drops to a certain degree of vacuum, the boiling point and freezing point of water coincide, and the ice can be directly vaporized into gas without being liquid. This process is called sublimation. The vacuum freeze-drying of food is to sublime and remove the frozen water in the food under the condition of low temperature and low pressure below the triple point of water, namely under the condition of low temperature and low pressure.
Since freeze-drying technology is carried out in a low temperature and low oxygen environment, most biological reactions are stagnant, and there is no liquid water in the treatment process. The water directly sublimates in a solid state, so that the original structure and shape of the material are protected to the greatest extent, and finally, high-quality dry products with both appearance and internal quality are obtained. At present, freeze-drying technology has been widely used in many fields, especially the use of this technology in food processing to obtain high-quality dehydrated food.


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