24
2023
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04
How to choose the cold trap temperature of a freeze-drying machine?
Freeze dryer is a new type of box that combines refrigeration system, vacuum system, heat transfer oil heating system, and dehumidification system, which can efficiently use the space inside the box to store materials for freeze vacuum drying.
Freeze dryer is a new type of box that combines refrigeration system, vacuum system, heat transfer oil heating system, and dehumidification system, which can efficiently use the space inside the box to store materials for freeze vacuum drying. At present, vacuum freeze-drying machines are suitable for drying various materials such as raw materials, traditional Chinese medicine slices, pharmaceutical intermediates, and food.
In the freeze-drying process, the form of freeze-dried materials is usually divided into solid and liquid. The stacking density of solids and the composition density of liquids both have an impact on the freezing time of materials. It is understood that there is a certain ratio of surface area to material thickness when materials are freeze-dried and packaged into containers.
Pre freezing of materials is the first thing that a freeze-drying machine needs to do during operation. Pre freezing can be divided into fast freezing and slow freezing, and the size of the crystals formed during freezing greatly affects the overall drying rate and the dissolution rate of the dried product.
The ice crystals produced by rapid freezing are smaller, while those produced by slow freezing are larger. Large ice crystals are conducive to sublimation, while small ice crystals are not conducive to sublimation. Rapid freezing leads to low sublimation rate and fast desorption rate; Slow freezing leads to a fast sublimation rate and a slow parsing rate.
Since the mass transfer rate is mainly determined by the temperature and pressure of the sublimation interface and the surface of the drying layer, there are two operations to increase the escape rate of water vapor in the drying layer: increasing the temperature of the sublimation interface to increase the Vapour pressure of water of the interface. Alternatively, increase the vacuum level of the drying chamber and reduce the vapor pressure on the surface of the drying layer.
Freeze drying with a cold trap temperature of -45 ℃ is suitable for some products that are prone to freeze-drying. Freeze drying machines with a cold trap temperature of around -60 ℃ are suitable for freeze-drying most products, while freeze-drying with a cold trap temperature of -80 ℃ is suitable for freeze-drying some special products.
The experiment on the effect of cold trap temperature on water harvesting capacity shows that when the cold trap temperature decreases from -35 ℃ to -55 ℃, the water harvesting capacity is significantly improved. However, when the cold trap temperature is lower than -55 ℃, the water harvesting capacity of the cold trap is not significantly improved. Therefore, in the absence of special needs, choosing a cold trap temperature of around -60 ℃ is an ideal choice.
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