Addtime： 2020-07-18 Browse times： 3278
1、 Vacuum drying
Vacuum drying is a drying technology. How is it defined? What is the principle?
Vacuum drying: the material to be dried is placed in a closed drying chamber, and the vacuum system is used to heat the dried material continuously while vacuumizing, so that the moisture in the material diffuses to the surface. After obtaining sufficient power, it overcomes the attraction between molecules and escapes to the low-pressure space of the vacuum chamber, and is pumped away by the vacuum pump. In this way, the material is dried.
In the process of vacuum drying, the pressure inside the drying chamber is lower than the atmospheric pressure, the number of gas molecules is small, and the density is low, so it can dry the materials easy to oxidize and deteriorate, disinfect and sterilize drugs and food to a certain extent, so as to inhibit the growth of some bacteria.
In the process of gasification, the temperature of water is directly proportional to the vapor pressure. Therefore, in vacuum drying, the moisture in the material can be vaporized at low temperature, realizing low-temperature drying, which is especially beneficial to some heat sensitive materials.
Vacuum drying can also eliminate the phenomenon of surface hardening under atmospheric pressure. Under the condition of vacuum drying, the pressure difference between the inside and the surface of materials is large. Therefore, under the effect of pressure gradient, water will move to the surface, and the surface hardening phenomenon will not occur. At the same time, it can improve the drying rate, shorten the drying time and reduce the operation cost. In addition, vacuum drying can overcome the phenomenon of solute dispersion. During vacuum drying, some dried materials contain substances or water, which can be recycled after drying, and harmful substances can also be recovered. Therefore, vacuum drying is also called "green drying".
In addition to the above advantages, by controlling the drying temperature and vacuum degree, the product can be expanded and foamed to produce crisp and instant food.
The equipment that can carry out vacuum drying is called vacuum drying equipment. Although it has many advantages, it needs to be equipped with a vacuum system. The vacuum sealing structure of transmission parts should be set at the inlet and outlet of the equipment. It should be inspected regularly in use. If it is damaged, it needs to be replaced in time. In addition, it has high manufacturing cost and high cost.
2、 Vacuum freeze drying
Before vacuum, the material is frozen to below the eutectic point temperature of the material in advance, and then vacuum drying is carried out after the material is completely frozen. According to its description, it can be seen that in addition to the advantages of vacuum drying, vacuum freeze-drying also has the following advantages:
1. It can keep the nutrient content and shape of the material unchanged;
2. The moisture content of freeze-dried materials can reach a very low level, which is convenient for long-term storage and long-distance transportation.
Do you understand the difference between the above two? I hope it is useful for you!
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