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What is the working principle of the freeze dryer?

February 17, 2022

Freeze dryer (also known as vacuum freeze dryer) originated from the vacuum freeze-drying technology in the 1920s. In the 21st century, vacuum freeze-drying technology has been widely used in fields other than medicine, biological products, food, blood products and active substances.




The freeze-drying machine has the following advantages compared with conventional drying methods (sun drying, drying, drying, spray drying, etc.)




*Many heat sensitive substances do not denature or inactivate.




*When drying at low temperature, the loss of some volatile components in the material is very small.




*In the process of freeze-drying, the growth of microorganisms and the role of enzymes cannot be carried out, so they can maintain their original properties.




*Because it is dried in the frozen state, the volume is almost unchanged, the original structure is maintained, and the concentration phenomenon will not occur.




*Since the water in the material exists in the form of ice crystals after pre freezing, the dissolved substances of inorganic salts originally dissolved in the water are evenly distributed in the material. During sublimation, the dissolved substances dissolved in water will precipitate, which avoids the phenomenon of surface hardening caused by the precipitation of inorganic salts on the surface due to the migration of water in the material to the surface in general drying methods.




*The dried material is loose, porous and spongy. It dissolves rapidly and completely after adding water, and almost immediately restores its original properties.




*Since drying is carried out under vacuum and there is little oxygen, some easily oxidized substances are protected.




*Drying can remove more than 95% ~ 99% of water, so that the dried products can be preserved for a long time without deterioration.




The working principle of freeze-drying mechanism is: after the liquid refrigerant absorbs the heat of the cooled material in the evaporator, it vaporizes into low-pressure and low-temperature steam, which is inhaled by the compressor, compressed into high-temperature and high-pressure steam, and then discharged into the condenser. In the condenser, it releases heat to the cooling medium (water or air), condenses into high-pressure liquid, and throttles into low-pressure and low-temperature liquid through throttling device, Enter the evaporator again to absorb heat and vaporize.




The refrigeration compressor sucks the low-pressure (low-temperature) refrigerant in the evaporator into the compressor cylinder, the refrigerant steam is compressed, and the pressure and temperature rise at the same time; The refrigerant steam with high pressure and high temperature is pressed to the condenser. In the condenser, the refrigerant steam with higher temperature exchanges heat with the cooling water or air with lower temperature. The heat of the refrigerant is taken away by water or air and condensed, and the refrigerant steam becomes liquid. This part of liquid is then transported to the expansion valve, throttled into low-temperature and low-pressure liquid through the expansion valve and enters the evaporator; In the evaporator, the low-temperature and low-pressure refrigerant liquid absorbs the heat of compressed air and vaporizes (commonly known as "evaporation"), and the compressed air condenses a large amount of liquid water after cooling; the refrigerant steam in the evaporator is sucked away by the compressor, so that the refrigerant will go through four processes of compression, condensation, throttling and evaporation in the system, so as to complete a cycle.