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Reasons affecting the working efficiency of freeze dryer
2019-04-12
Freeze drying machine can freeze material in a very short time, for some special factory or merchants box is an important equipment, ordinary working principle of the freeze dryer is very simple, namely heat transfer, but there are many factors that can affect heat and quality transmission, they will affect the transfer efficiency to a certain extent, which affects the efficiency of the frozen.
1. Morphology and composition of materials
According to the form of freeze-dried materials, they are usually divided into solid and liquid. The form of solid and the concentration of liquid have great influence on the freeze-drying rate.
2. Pre-freezing rate
The size of the crystals formed during freezing greatly affects the rate of drying and the rate of dissolution of the dried product. The differences between quick freezing and slow freezing are as follows: quick freezing produces smaller ice crystals, while slow freezing produces larger ice crystals. Large ice crystals are favorable for sublimation, while small ice crystals are unfavorable for sublimation. Rapid freezing leads to low sublimation rate and fast desorption rate. Slow freezing results in fast sublimation rate and slow resolution rate.
3. Pressure in drying chamber
The level of pressure in the drying chamber of ordinary freeze dryer affects the rate of heat transfer and mass transfer. In terms of mass transfer, the lower the pressure, the better, while for heat transfer, the higher the pressure, the better. The mass transfer rate is mainly determined by the temperature and pressure of the sublimation interface and the dry layer surface. To increase the water vapor escape rate in the dry layer, firstly, the temperature of the sublimation interface should be raised to increase the water vapor pressure at the interface. The second is to improve the vacuum degree of the drying chamber and reduce the steam pressure on the surface of the drying layer.
4. Heat transfer mode
According to the traditional classification can be divided into: conduction, convection, thermal radiation and medium heating (microwave heating). Since the process of sublimation drying involves the transfer of heat and mass (water vapor), the drying rate is greatly affected by which heat transfer method is adopted to transfer heat more effectively to the material.
5, the load
When materials are lyophilized, there is a certain ratio of surface area to material thickness after they are divided into containers, that is, lyophilized is related to the loading volume. Small surface area and thickness are favorable for water sublimation, easy freeze-drying and good quality. When drying, the wet heavy load of drying on the unit area tray is an important factor to determine the drying time. In general, the thinner the thickness of material accumulation, the faster the heat and mass transfer speed, and the shorter the drying time. However, thin material thickness leads to less drying material per batch per unit freeze-dried area, which is unfavorable to increase the output per unit freeze-dried area and per unit time.
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