The working principle of freeze dryer is based on the three-phase change of water. It freezes the material at low temperature and sublimates ice directly into water vapor in a vacuum environment to achieve drying.
The working principle of freeze dryer (vacuum freeze dryer) is mainly divided into the following three stages, combining the three-phase change in physics and vacuum technology:
1. Freezing stage
Quickly cool the water-containing material to below its eutectic point temperature (usually -50℃ to -20℃), so that the water is completely solidified into ice crystals to form a porous solid structure.
Purpose: To avoid the collapse of the material structure during subsequent sublimation and provide a channel for water vapor to escape.
2. Sublimation drying stage (main drying)
Vacuum environment: The pressure drops below the triple point pressure of water (about 611 Pa or lower), so that ice is directly sublimated into water vapor.
Heating assistance: Provide heat through conduction, radiation, etc. (the temperature needs to be controlled below the material disintegration point) to accelerate the sublimation of ice crystals.
Condensation capture: Water vapor is frozen by a cold trap (condenser) at -40℃ to -80℃ to maintain the system at a low pressure.
3. Analytical drying stage (secondary drying)
Remove bound water: Increase the temperature (such as 20℃ to 50℃) and extend the vacuum time to remove the residual water adsorbed on the surface of the material molecules, and the final water content can be reduced to 1%-5%.
Core principle: Utilize the triple point of water (0.01℃, 610.5Pa) characteristics to achieve direct sublimation of solid ice to gas at low temperature and low pressure to avoid liquid water from destroying the material structure.
Advantages:
Low temperature protection: Suitable for heat-sensitive substances (such as proteins, vaccines).
High rehydration: The porous structure retains the original form of the material and recovers quickly when exposed to water.
