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Views: 202 Author: Wendy Publish Time: 2023-05-23 Origin: Site
The operating principle of a vacuum freeze dryer, also known as a freeze dryer, can be described simply as follows: in a vacuum, low-temperature environment, the water in the material is frozen into a solid and subsequently transformed into a gas for sublimation, resulting in the production of freeze-dried material.
According to the theory of thermodynamic phase equilibrium, the triple point of water (where vapor, liquid, and solid exist simultaneously) has a temperature of 0.0098°C and a pressure of 609.3pa (4.57mm/mg). Ice crystals can immediately transform into gaseous water vapor during the phase shift of water when the pressure is lower than the triple point of the substance. This process is known as sublimation. With the use of this product, materials with a lot of water can be pre-frozen, converting any free water crystals present into solids, before the ice crystals are sublimed under vacuum. A portion of the materials' adsorbed water is released after the ice crystals sublimate, leaving behind frozen Dry substance.
Under normal circumstances, 95-99% of the moisture can be removed by freeze drying.
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.
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.
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)℃,
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.
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.
