Vacuum freeze-dryer is a vacuum freeze-drying equipment for materials, which is suitable for drying high-grade raw materials, Chinese herbal pieces, seafood, wild vegetables, dehydrated vegetables, food, fruits, chemical and pharmaceutical intermediates and other materials. The working temperature of vacuum freeze dryer is one of the important parameters that affect its work. Generally, there are two cooling temperatures, namely, the cooling temperature of the plate and the cooling temperature of the condenser. There are three main types:
1. The refrigeration system adopts single-stage refrigeration compression cycle, and the refrigeration temperature of plate is about -35 ~-40℃, and that of condenser is about -50℃. This freeze-dryer is suitable for producing some products that are easy to freeze-dry.
2. The refrigeration system adopts two-stage refrigeration compression cycle, the refrigeration temperature of plate is about -45 ~-50℃, and the refrigeration temperature of condenser is about -65℃. The freeze-dryer is suitable for the freeze-drying of most medicines.
3. The refrigeration system adopts cascade refrigeration cycle, and the refrigeration temperature of plate is about -55 ~-60℃, and that of condenser is about -75℃. The freeze-dryer is suitable for freeze-drying some special products.
Second, the vacuum degree of the vacuum freeze-dryer is normal.
In addition to the working temperature, the vacuum freeze dryer also has an important parameter that affects the production, namely the vacuum degree. So what is the freeze-drying degree of vacuum freeze-dryer?
When the freeze-dryer works, the pressure in the freeze-drying room is limited. Low pressure is conducive to the sublimation of ice, but too low pressure is not conducive to heat transfer, the product is not easy to get heat, and it is easy to cause uneven internal temperature distribution of the product, and local temperature will collapse if it is too high. When the pressure is too high, the sublimation speed of ice inside the product will slow down, and the heat absorbed by the product will decrease, so the temperature of the product itself will increase. When it is higher than the melting point of * * * *, the product will melt, leading to freeze-drying failure.
The experiment shows that when the pressure in the freeze-drying chamber of the freeze-dryer is lower than 65438±00Pa, the conduction and heat transfer of gas can be ignored. When the pressure is greater than 30Pa, the convective heat transfer of gas is obviously enhanced. Generally speaking, the appropriate pressure within the vacuum control range of freeze-dryer is 10-30Pa.
What is the freeze-drying area of the vacuum freeze dryer?
The freeze-drying area of vacuum freeze-dryer is generally reflected in the model. For example, the freeze-drying area of CVD- 18 freeze-dryer is 0. 18_. In the selection, the freeze dryer with large freeze-drying area is generally calculated according to the materials that need to be freeze-dried.
For example, for each batch of products with liquid volume of 1.8kg (L) to be freeze-dried, materials are loaded into material trays, and the thickness of each tray is 10_, then the loading area of freeze-dried plates can be calculated:
A (area, _)=V (volume, m)/H (height, m) = 0.0018m/0.01m = 0. 18 _, that is, the load area should be selected as 0.18 _.