How does a Freeze Dryer work?
The working process of a freeze dryer can be simply described as follows. It can pre-freeze materials that need to be dried in order to make materials in the solid form. Making use of the direct sublimation property of ice, it can dehydrate materials and dry them into powder under conditions of low temperature and low pressure.
Specifically speaking, a freeze dryer works in three periods. The first period is the freezing, which can preserve the physical form of materials. The second period is the primary drying or sublimation, which reduces pressure and heats materials to sublimate water. Primary drying may be a slow process, but approximately 95% of water in materials is removed at this stage. The third period is the secondary drying or absorption, during which the ionically-bound water molecules are removed. The complete working process is finished. Most materials can be dried to 1-5% residual moisture.
Applications of a Freeze Dryer
As one of the types of necessary drying equipment, the freeze drying equipment can be widely used in biological, chemical and pharmaceutical fields. It is usually used to dry heat sensitive materials that are thermally unstable and easy to oxidize and deteriorate, as well as the materials that are unstable in aqueous solutions and need to maintain biological activity.
Pros and Cons of a Freeze Dryer
A freeze dryer possesses both pros and cons. On the one hand, it can get rid of more than 95-99% moisture. Some easily oxidized materials can be prevented from oxidizing and can be preserved for a long time owing to the vacuum working condition. On the other hand, the freeze drying equipment is complicated and the process control requirements are relatively high, with a high energy consumption and long time for freeze drying.