The fundamental principle in freeze drying is sublimation, a water remove process based on freezing the raw material to solid phase, reduce surround pressure and proper give energy, enable water sublime from solid phase(ice) to gas phase(vapor), the sublimation drying process skip liquid phase.
Like its name: Vacuum Freeze Drying, the major factors is pressure and temperature (freezing to minus or heating above 0), the phases(solid,liquid,gas) could flexible transform under a certain range pressure, see water phase diagram.
From the chart, we could very easy understand the phases interconversion condition (at what temperature, what pressure), also this is exactly freeze drying machine design principle: refrigeration compressor system provide cooling energy to shelves and condensing coils, vacuum pumps connect drying chamber, heating system connect shelves.
The general process of freeze drying machine:
- Material load to trays and put on shelves, compressor system cooling the shelves and freezing materials to minus.
- After material complete frozen, stop cooling shelves, start cooling condenser coils.
- Vacuum the drying chamber and proper/gradually give energy to shelves support sublimation.
- Vapor from raw material flows to condenser room and condensing onto coils surface, turn to ice form again.
- The process continues until all water in raw material move to condenser room.
- Dried material quick pack. In the same time, condenser defrosting by hot water spraying.
- Drying process finish and prepare another batch.