The freeze dryer is a device that uses refrigeration combined with vacuum and then is electronically controlled. Refrigeration is the drying process of pre-frozen materials to be followed by vacuum sublimation. In addition, the refrigeration cold well is also critical to capture the sublimated moisture, so the temperature and cooling capacity of refrigeration are very important. Another important link is vacuum. The effect of vacuum determines the ability of sublimation.
As the saying goes, no one is perfect, everyone has strengths and weaknesses, so do machines. Vacuum freeze dryers also have advantages and disadvantages. With the development of technology, there are many drying methods, such as sun drying, air drying, high temperature drying, spray drying, and low temperature freeze drying.
Ordinary drying methods (such as sun drying, air drying, high temperature drying, spray drying) are usually carried out at temperatures above 0°C or higher. The dried products generally have the problems of reduced volume and hard texture. Most of the volatile components will be lost. Some heat-sensitive materials will be denatured and deactivated, and some materials may even be oxidized. Therefore, there is a big difference in the properties of the product after drying compared with that before drying.
The vacuum freeze dryer is a low-temperature freeze-drying method. Its principle is to freeze the water-containing material into a solid state, and then sublime the water from the solid state into a gaseous state, thereby removing the water and preserving the material.
Compared with ordinary drying methods, the vacuum freeze dryer has the following advantages:
1. Many heat-sensitive substances will not be denatured or inactivated.
2. When drying at low temperature, some volatile components in the substance lose very little.
3. During the freeze-drying process, the growth of microorganisms and the action of enzymes are impossible, so the original properties can be maintained.
4. Since the drying is carried out in a frozen state, the volume is almost unchanged and the original structure is maintained without concentration.
5. Since the moisture in the material exists in the form of ice crystals after pre-freezed, the dissolved inorganic salt substances originally dissolved in the water are evenly distributed in the material. During sublimation, the dissolved substances dissolved in the water are precipitated, which avoids the phenomenon of surface hardening caused by the precipitation of inorganic salts carried by the water inside the material to the surface by the general drying method.
6. The dried material is loose, porous, and sponge-like. After adding water, it dissolves quickly and completely, and restores its original properties almost immediately.
7. Since the drying is carried out under vacuum, and there is very little oxygen, so some easily oxidized substances are protected.
8. Drying can remove more than 95% to 99% of moisture, so that the dried product can be stored for a long time without deterioration.
The main disadvantage of vacuum freeze dryers is their high cost. Because it needs vacuum and low temperature conditions, the vacuum freeze dryer must be equipped with a vacuum system and a low temperature system, so the investment and operating costs are relatively high.
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