From the working principle of the freeze dryer, the freeze dryer can be regarded as the structure of two large refrigerators plus a vacuum pump. One of the refrigerators is responsible for freezing the freeze-dried product into ice cubes, and then a vacuum pump creates a low vacuum environment.
Under the reduced pressure environment, the thermal constants such as the boiling point and melting point of the object are correspondingly reduced. Therefore, the product in the freeze dryer can be sublimated from a solid to a gas at low temperature after being slightly heated.
The gas then flows to another large refrigerator, where it is captured and re-condensed into ice cubes. When the water of the medicine is completely drained, a freeze-drying process is completed.
In the operation of the freeze-drying machine, the control of the eutectic point (or eutectic point) temperature of the product has a great influence on the freeze-drying effect. The so-called eutectic point is the temperature at which all the solution condenses.
Commonly used eutectic point measuring instruments are mainly based on the principle of sudden change of resistivity during phase transition.
Generally speaking, experienced users can obtain the eutectic point (or eutectic point) temperature by observing the change of product properties through the viewing window during the pre-freezing stage.
When the product begins to freeze, the temperature detected by the thermocouple immersed in the product suddenly rises due to the exothermic phenomenon of the freezing process.
More than 90% of the water is removed before the eutectic point (or eutectic point), this process can be called sublimation drying or primary drying.
It is also important to judge the time at which the primary drying ends. Too early or too late will cause changes in freeze-dried quality. The intuitive way to judge whether the primary drying is over is to judge according to the shape of the product.
At the end of the primary drying, most of the moisture is removed. It can be observed that there is also a water line on the product that continues to drop until it disappears.
The disappearance of the waterline means that a drying session is coming to an end. The second method can be judged according to the change trend of the pressure in the freeze-drying chamber. When most of the pressure in the freeze-drying chamber is removed, the pressure in the freeze-drying chamber will continue to drop until it is linear.
The third method can be judged according to the change of product temperature. When most of the water has been removed, the temperature of the freeze-dried product will be closer to the shelf temperature.
Application of Freeze Dryer
