A freeze dryer is one of the most common and essential drying equipment, which is used to dry items by utilizing the freeze drying technology. It usually consists of four components, including a drying chamber, a vacuum pump, a heat source and a condenser.
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, the working of a freeze dryer can be classified into 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 dryer 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.
Does Freeze Drying Kill Bacteria?
It’s known that the freeze drying is a water removal process which is primarily used for preserving perishable materials or making them more convenient for transport. Research indicates that the freeze drying can decrease the number of bacteria to a certain extent, but can’t kill all of bacteria. Some bacteria will go into a dormant state and still stay alive in the frozen materials. When the environment becomes favorable, bacteria will return to a normal state.
Advantages and Disadvantages 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.