Factors related to freeze-drying quality of freeze dryer

Vacuum freeze dryer is called freeze dryer for short. According to the specifications, it can be divided into laboratory freeze dryer, pilot freeze dryer and production freeze dryer. The factors that affect the freeze dryer drying process and freeze drying quality, that is, an ideal freeze drying curve, are subject to factors such as material properties, concentration, sublimation area, eutectic point, heat transfer medium and method, equipment performance and so on.

The main factors affecting the freeze-drying quality of the freeze dryer:

1. The thickness of the material directly affects the drying time, because the thicker the material, the greater the resistance to heat and mass transfer, the more difficult it is for the moisture inside the material to transfer outward, so the drying time is longer.

2. Pre-freezing temperature and maintenance time. If the pre-freezing is not done properly, the material may "boil" when entering the sublimation drying stage, or the surface of the freeze-dried product may be uneven after being frozen, affecting the appearance. If the temperature is too low, energy and time are wasted. The time required for pre-freezing should be determined according to different specific conditions. But the general principle is that all parts of the product should be completely frozen.

3. The temperature (or heat supply) of the sublimation interface and the ability of water vapor to escape the product. The former is mainly determined by the temperature of the partition and the pressure (vacuum degree) of the drying box, while the latter is mainly determined by the temperature of the sublimation interface (corresponding to the saturated pressure of water vapor) and the partial pressure of water vapor in the box.

The vacuum freeze dryer is a low-temperature freeze-drying method. Its principle is to freeze the water-containing substance into a solid state first, and then sublime the water in it from the solid to the gas, thereby removing the water and preserving the substance.