Vacuum freeze dryer is also called freeze dryer, usually its working principle is simply understood as: in a vacuum low temperature environment, the water in the material is frozen into solid, and then converted into gas for sublimation, so as to obtain freeze-dried material.
According to the thermodynamic phase equilibrium theory, the temperature of the triple point of water (the coexistence of vapor, liquid and solid) is 0.0098℃, and the pressure of the triple point of water is 609.3pa (4.57mm/mg). During the phase change of water, when the pressure is lower than the triple point of water, solid ice can be directly converted into gaseous water vapor, that is, ice crystals sublimate. This product is to pre-freeze materials containing a large amount of water to solidify the free water crystals in the materials into solids, and then sublime the ice crystals in the materials under vacuum conditions. After the ice crystals sublimate, part of the adsorbed water in the materials is removed, and then frozen Dry material. Under normal circumstances, 95-99% of the moisture can be removed by freeze drying.
What are the main components of the vacuum freeze dryer?
1, drying warehouse
It is a sealed container with the functions of vacuuming and heating and drying. The sublimation and drying process of the material is completed in the drying bin. The materials are placed in stainless steel trays on the shelf in the drying room. Each shelf has a probe for measuring the temperature of the material, which is used to monitor the temperature of the material during the entire freeze-drying process.
2, water catcher (cold well)
It is a closed device for condensing and sublimating water vapor, usually located at the back of the drying box. There is a large area of metal adsorption surface inside. The sublimed water vapor in the drying chamber can be condensed and adsorbed on the metal surface. The working temperature of the adsorption surface can reach -45℃~-65℃. The shape of the condenser is a cylinder made of stainless steel or iron. There are condenser tubes inside, which are respectively connected to the refrigeration unit to form a refrigeration cycle system.
3, heating system
The function of the heating system of the freeze dryer is to heat the materials in the drying bin, so that the materials are continuously heated and sublimated to meet the specified moisture content requirements. The heating method of the heating system of the freeze dryer is mainly divided into contact heating and radiant heating.
Contact heating adopts circulating medium heating method. When the heating system is working, the circulating liquid is heated first, and the liquid temperature is automatically controlled by the temperature selected by the liquid tank control regulator. After the pipeline pump is started, the circulating fluid enters the shelf in the drying box to heat the shelf, and then returns to the fluid box for heating cycle. When the circulating medium is silicone oil, the high temperature of the diaphragm can reach (+60~+70)℃,
4, vacuum system
The vacuum system consists of a vacuum pump and a roots vacuum pump. Roots pump is a booster pump and cannot be used alone. The vacuum pump must be started and allowed to work for a period of time. When the system vacuum reaches below 1kPa, the Roots pump will automatically start. The structure of the vacuum pump and Roots pump is shown in the instructions. The vacuum gauge of the vacuum system can use an electric contact vacuum gauge, which automatically controls the start of the Roots pump according to the pre-selected vacuum value.
5. Refrigeration system
The refrigeration system of vacuum freeze dryer is composed of refrigeration compressor unit, R22 or R404A refrigerant. Generally speaking, the quick-freezing refrigeration system and the water trap refrigeration system of the freeze-drying equipment share the same refrigeration system. When the system is working, the shelf temperature can be reduced to -35°C in the contact heating mode. When the refrigeration system is working, the surface temperature of the condensing coil can reach -35～-65℃. According to user needs, a low-temperature screw or two-stage piston refrigeration compressor unit can be used. Generally speaking, a two-stage piston compressor has a better cooling effect and a lower cooling temperature.