Freeze Drying Theory
Freeze drying, is a dehydration process typically use to preserve perishable materials or make the material more convenient for storage. In pharmaceutical area, freeze drying called lyophilization, they are synonymous.
The definition of freeze drying or lyophilization is to dry something in a solid state and is under vacuum environment.
Thus, freeze drying removes water by freezing the material, and then reduce the surrounding pressure, proper apply heat to allow the frozen water in the material to sublime directly from solid phase to gas.
Water Triple Points Diagram: A graphic shows the water phases
Freeze Drying System Works: Vapor Flows.
Freeze Drying Works?
As above picture shows, the 3 phases of water (Vapor, Solid, Liquid) can flexible convert, the most matters are Pressure and Temperature. For freeze drying, also works base on the water triple point diagram, solid phase and vapor phase have intersections, where pressure and temperature both lower than Triple Point. Which means:
Vapor phase go through the border and convert to solid phase will called condensing. On opposite, Solid phase go through the border and convert to vapor phase will called sublimation.
Freeze drying systems are built base on the principle: The drying chamber uses sublimation technology to remove products' water, since the removed water must go to somewhere, so an ice bank is installed and uses condensing technology to temporarily store the trapped vapors. After drying finish, melt the ice and release out of freeze dryer.