Normally, the boiling point of water at one atmospheric pressure is 100°C, but through a special method, the boiling point of water can be reduced to 80°C, 60°C or even 40°C.
I think everyone must have heard of this method. This is the vacuum drying technology we will talk about next!
In simple terms, vacuum drying technology is to place the material in an environment with vacuum negative pressure, and appropriately heat the material to the boiling point under the negative pressure state or reduce the temperature to solidify the material, and then dry the material through the melting point.
In detail, the melting point and boiling point of the water in the material under negative pressure will decrease as the vacuum degree increases. At the same time, the water vapor content is reduced through the work of the vacuum pump, so that the water and other solutions in the material can obtain enough kinetic energy to separate from the surface of the material. Vacuum drying can keep the original characteristics of materials that are easy to be oxidized and other chemical changes during the drying process due to the isolation of air under negative pressure. This is the reason why water can evaporate at other temperatures!
Because the vacuum drying technology requires the air to be removed from a closed container and dried by reducing pressure, it is also called drying under reduced pressure.
Nowadays, vacuum drying technology has been very well applied in many different fields! For example, in the production of health food, especially the extraction of natural products, because many components in natural products are not resistant to high temperatures, the application of vacuum drying technology can perfectly solve this problem.
Vacuum drying principle:
In the various heating and drying methods under normal atmospheric pressure, due to the heating of the material, its own characteristics (such as the color, fragrance and taste of the food) will be lost to a certain extent. If the vacuum drying method is adopted, because the air is isolated under negative pressure, some materials that are prone to chemical changes such as oxidation during the drying process can better maintain their original characteristics. Vacuum drying is to place the dried food materials in a closed drying room. While the vacuum system is used to vacuum, the dried materials are appropriately and continuously heated so that the water molecules inside the materials can obtain sufficient kinetic energy to be pumped away by the vacuum pump.
The various vacuum drying methods can be divided into two fundamentally: through melting point and through boiling point.
1. Melting point
Melting point drying is also called freeze drying. In the drying process, the wet material is first frozen into a solid state at a lower temperature, and then under a high vacuum (common: 130～0.1Pa), the solid moisture is directly sublimated into a gaseous state and removed The process is also called sublimation drying. The necessary condition for achieving this vacuum drying is that the pressure of the drying process should be lower than the saturated vapor pressure of ice at the operating temperature.
Wet materials can also not be pre-frozen, but the materials will be frozen by themselves when the moisture vaporizes and absorbs heat in a high vacuum. This kind of freezing energy consumption is small, but it is easy to cause foam or splash phenomenon to the liquid material and cause loss.
The sublimation temperature during the drying process is generally -35-5 ℃, and the extracted water can be frozen and accumulated on the condenser or directly discharged through a vacuum pump.
The vaporization speed of water when boiling is much faster than the vaporization speed when evaporating, the evaporation of water into steam can be carried out at any temperature. Water boils into steam, which can only be done at a certain temperature, but when the pressure is reduced, the boiling point of water also decreases. The vacuum dryer is to provide a heat source in a vacuum state, and supply sufficient heat to the moisture in the material through heat conduction and other heat transfer methods, so that evaporation and boiling are performed at the same time, and the vaporization speed is accelerated. At the same time, the vaporized steam is quickly extracted while vacuuming, and a negative pressure is formed around the material. A large humidity gradient is formed between the inner and outer layers of the material and between the surface and the surrounding medium, which accelerates the vaporization speed and achieves rapid The purpose of drying.
In addition, the factors affecting vacuum drying mainly include relative density of concentrated liquid, vacuum drying temperature, vacuum drying vacuum degree, vacuum drying time, etc.
Common vacuum drying equipment: vacuum drying oven, continuous vacuum drying equipment, etc.
Vacuum drying extends to many different industrial applications, such as wood drying, food drying, and ceramic drying. It can be said that our life in the clothing, food, housing and transportation need vacuum drying.
So how is “vacuum” as the core keyword of vacuum drying achieved?
Here, a vacuum pump is needed to achieve vacuum. The vacuum pump provided by Shanghai EVP Vacuum Technology Co., Ltd. can meet the needs of different models/different sizes of vacuum drying machine, Common vacuum pumps is:
1.2BE liquid ring vacuum pump, the ultimate vacuum is 33hpa, and the gas volume is 246m3/h-9450m3/h.
2.H piston vacuum pump, the ultimate vacuum is 1-0.06pa, and the capacity is 54m3/h-1080m3/h
3. ZJP roots vacuum pump, the ultimate vacuum is 0.05pa, and the capacity is 252m3/h-4320m3/h
4.LG dry screw vacuum pump, the ultimate vacuum is 2pa, and the capacity is 180m3/h-1080m3/h
The selection of pump model is also based on the detailed requirements. EVP Vacuum has extensive experience in the vacuum drying technology, please feel free to communicate any questions.
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