The freeze dryer uses the freeze-drying technology, that is, the method of freezing the aqueous material into a solid state, and then sublimating the water from the solid state into a gaseous state, so as to remove the water and preserve the material. Water has three phases: solid, liquid and gaseous. According to the phase equilibrium theory in thermodynamics, with the decrease of pressure, the freezing point of water changes little, but the boiling point is getting lower and lower, close to the freezing point. When the pressure drops to a certain vacuum, the boiling point and freezing point of water coincide, and ice can be directly vaporized into gas without liquid. This process is called sublimation. Freeze drying of food is to sublimate and remove the frozen water in food below the three-phase point of water, that is, under the condition of low temperature and low pressure.
First of all, when using the freeze dryer for the first time, we must thoroughly clean all parts of the freeze dryer. As we all know, stainless steel parts are cleaned with ethanol and plexiglass is cleaned with salt water. The ampoules of freeze dryer are cleaned by ultrasonic cleaning machine. However, what preparations do we need to do before operating the freeze dryer?
The vacuum freeze dryer needs to be pre frozen before operation. The pre freezing needs to prepare a low-temperature refrigerator at minus 40 ℃ or minus 80 ℃. It usually takes about four hours to place the items to be dried in the low-temperature refrigerator or liquid nitrogen. It can be observed directly from the outside. After the items are completely frozen and firm, Before the freeze-drying experiment can be carried out, the articles can be quickly moved to the tray of the freeze dryer to ensure the freeze-drying effect.
