Basic Operating Principle
Under high-vacuum conditions, this device removes water from inside material frozen in advance after sublimating the water from an ice state to a water vapor on the basis of the sublimation principle, thus drying the material.
Vacuum freeze drying is widely used in various products to ensure no loss of such nutritional ingredients as protein, vitamins and others in food, especially easily volatile and temperature-sensitive ingredients, thus maintaining the original nutrition to the maximum extent. In addition, it can effectively prevent oxidation during the drying process, thus avoiding the conversion and status variation of the nutrition. Lyophilized products look spongy with no shrinking, favorable reconstitution properties and little water content; after appropriate packaging, they can be preserved and transported for a long time under normal temperatures.
1. Systematic preparations
Verify that the system is clean and dry, and the vacuum pump and refrigerator are connected with the power on; check the airtight seal of the exhaust port and cryotube.
2. Adding the sample
The sample shall be precooled to at least －40℃ in a deep cryogenic refrigerator (－70℃) or liquid nitrogen (－196℃). Turn on the switch of the seal pipe, remove the freezing chamber and place the sample on the clapboard inside the freezing chamber. Turn off the switch of the seal pipe.
Turn on the freezing switch and wait for 20～30 minutes until the temperature of the freezing chamber is lower than －40℃.
4. Vacuum pumping
Turn on the vacuum pump switch and wait for 10～15 minutes until the system pressure is lower than 100 millitorr.
5. Monitoring process
Ensure the system's parameters (cryogenic temperature and vacuum pressure) are within the normal range;
Periodically check the freezing conditions in the freezing chamber to decide if defrosting is necessary;
Verify whether the drying of the sample is thorough; the drying process may generally take 24～72 hours, which is determined through visual inspection with regard to specific samples.
6. Shutting the system down
Shut off the main switch and connect the exhaust pipe or turn on the switch of the seal pipe to relieve the vacuum state.
Turn off the vacuum switch and the freezing switch, and take the sample out.
7. System maintenance
Defrosting: in case of frost inside the compression chamber below the freezing chamber, connect up the exhaust pipe and use a small amount of water (not more than one half of the capacity of the compression chamber) to facilitate the melting of the frost. During defrosting, it is prohibited to knock on the ice.
Dehumidification: water spray on the compression chamber, freezing chamber, vacuum pump compressor and washer must be wiped dry.
Cleaning: use a gentle type of detergent or soda water to clean the compression chamber and freezing chamber; dry and remove the exhaust pipe, then seal the exhaust holes again.
Oil pumping: check the oil level periodically to remove oil frost.
1. The sample shall be kept frozen and free from 'back melting'.
The majority of solvents have a freezing point higher than －40℃, so the freezing chamber with its temperature of lower than －40℃ can maintain a sample in an iced state.
It is advisable to produce frozen samples in pieces smaller than 20mm to avoid the 'back melting' of the sample.
2. Poisonous or corrosive samples
It is best not to freeze or dry such samples; if it is required, take system maintenance measures and order a specific filter separately to protect the vacuum pump.
3. Vacuum pump oil shall be kept clean.
Yellowish or colorless oil is clean. If the color is becoming darker, it indicates that there is acid pollution, while vaporific turbidity indicates water pollution. If pollution is found, replace the oil with clean oil.
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