Difference between freeze drying equipment and vacuum freeze drying equipment
Freeze drying equipment and vacuum freeze drying equipment are really different.
There are two kinds of freeze-drying: air freeze-drying and vacuum freeze-drying.
1. Air freeze drying: the compressed air is cooled to a certain dew point temperature by the refrigeration equipment, and the corresponding moisture is separated by the separator for gas-liquid separation, and then the water is discharged by the automatic drain valve, so that the compressed air can obtain the required dry dew point.
General process flow:
Air flow - the compressed air enters the precooling cooler from the air inlet for preliminary cooling, flows into the evaporator of the refrigeration system for further cooling. The cooled compressed air passes through the air-water separator, and the condensate is discharged by the automatic drainer. The dried and cooled compressed air returns to the heat exchanger for temperature return, and leaves the frozen dryer through the air outlet.
Refrigerant process: the refrigerant is compressed by the refrigeration compressor to a liquid state of high temperature and pressure. The liquid refrigerant in high temperature and pressure state is cooled by the condenser (air cooling or water cooling), then it becomes the refrigerant in medium temperature and high pressure state, and the impurities are filtered by the drying filter. The refrigerant becomes the gas-liquid mixed state of low temperature and pressure through the action of capillary, and finally enters the evaporator and the evaporator After the heat exchange of hot compressed air, complete the refrigeration work, and return to the refrigeration compressor for circulation work.
2. Vacuum freeze-drying: freeze the water bearing materials below the freezing point, turn the water into ice, and then sublime the ice under high vacuum to remove. The water vapor generated by sublimation is removed by condenser. The heat of vaporization needed in the sublimation process is generally supplied by thermal radiation.
General process flow:
Pre freezing stage: firstly, the water in the object is frozen into ice, so that the dried object has the same shape as before. The pre freezing temperature is lower than the eutectic point temperature of the material.
Sublimation drying stage: one stage drying. After pre freezing, vacuumize, at this time, the water in the object is directly sublimated from ice to vapor. Since the gasification process absorbs heat, it should be heated by shelf at this time. Because of the pressure difference between the drying oven and the condenser, the water vapor enters the condenser continuously and the sublimation continues until the end of the sublimation stage. In this process, the temperature and pressure should be controlled below the eutectic point of the object so as not to cause ice melting.
Analytical drying stage: in some cases, two-stage drying is required. Some objects contain adsorbed water (such as the water adsorbed on the capillary wall inside the object or on the sex gene), which is not frozen. In order to remove this part of water, it is necessary to supply enough heat to heat up the object, as long as it does not deteriorate due to overheating (generally up to 30-50 ℃), which is also a vacuum environment.
Vacuum freeze-drying is only one of the methods of freeze-drying, but it is often confused with vacuum freeze-drying because it is widely used, especially in schools and scientific research institutions.