Vacuum freeze drying system working principle and composition
Vacuum freeze-dryer is referred to as lyophilizer and its core part is refrigeration system. The performance of the refrigeration system determines the performance of the vacuum freeze-dryer. How to ensure its stability, we can only understand the refrigeration aspects to analyze and study the operation state of the refrigeration system.
Refrigeration cycle refrigeration system consists of refrigeration compressor, condenser and evaporator, the throttle device of four basic parts, through the pipes, to form a closed system. The refrigerant is constantly circulating in the system, and the heat exchange between the outside and the change of phase state is carried out to achieve the purpose of cyclic refrigeration.
Its working principle is: the liquid refrigerant in the evaporator, after absorbing heat is cooling material vaporized into low pressure low temperature steam, in the compressor, compressed into high temperature and high pressure steam back into the condenser, the condenser to the cooling medium (air or water) in the exothermic, condensation of high pressure liquid, the throttle device throttling for low pressure low temperature liquid, again into the evaporator heat vaporization.
Refrigeration system basic common sense: in order to more effectively solve the lyophilizer in analytic drying stage compressor to run almost no-load condition in long-term work, and make the low evaporation temperature caused by suction pressure oil return difficult, small and medium voltage is too low, high exhaust pressure makes lubrication, inspiratory pressure caused by small and medium voltage is too low, high exhaust pressure lubricating oil carbonization or refrigerant decomposition and a series of problems, you can add some other measures in the system.
No matter what kind of drying, it is essential to remove moisture from the material. Vacuum freeze drying is the removal of sublimated water from a material at low temperature and pressure. Therefore, the vacuum system of the vacuum freeze-dryer must be able to remove water vapor, and according to the requirements of the freeze-dryer process, the no-load limit vacuum degree of the medical freeze-dryer should reach 1Pa, and the no-load limit vacuum degree of the food freeze-dryer should reach 10Pa. The vacuum system must also be capable of pumping water and steam at sufficient speed.
The vacuum pump of vacuum system had better choose to be able to remove part of the water vapor, in case the performance of vacuum freeze dryer becomes bad, the water vapor enters the vacuum pump, causing the pump oil emulsification, the vacuum degree is reduced. If roots water ring pump set or roots rotary vane pump, slide valve pump set, the requirements of rotary vane pump or slide valve pump is with air ballast. In order to shorten the pumping time, it is best to install a water ring pump, directly connected with the freeze-drying chamber.