What are the factors that affect the efficiency of the freeze dryer?
The whole process of freeze-drying is actually the simultaneous process of heat transfer and mass transfer (steam). The heat and mass transfer rate affect the drying rate, which affects the entire freeze-drying cycle. All the factors affecting heat and mass transfer will affect. Drying rate. The main factors that affect heat and mass transfer are:
1. Form and composition of materials
According to the form of the lyophilized material, it is usually classified into a solid and a liquid. The morphology of the solids and the concentration of the liquid have a greater effect on the freeze-drying rate.
2, pre-freezing rate
The size of the crystal formed upon freezing greatly affects the rate of drying and the rate of dissolution of the product after drying. The quick freezing and slow freezing processes have the following differences: ice crystals produced by quick freezing are smaller, and ice crystals produced by slow freezing are larger. Large ice crystals are good for sublimation. Small ice crystals are not conducive to sublimation. Rapid freezing leads to low sublimation rate and fast desorption rate. Slow freezing leads to fast sublimation rate and slow resolution rate.
3, the amount
When the material is lyophilized, there is a certain ratio of surface area to material thickness after being dispensed into the container, that is, lyophilization is related to the loading. The surface area and thickness are small, which is beneficial to the sublimation of water, easy to freeze and the quality is ideal. When drying, the wet weight loading per unit area of ​​the tray is an important factor in determining the drying time. Under normal circumstances, the thinner the thickness of the material accumulation, the faster the heat transfer and mass transfer rate, and the shorter the drying time. However, if the thickness of the material is thin, the amount of material dried per batch per unit of lyophilized area is small, which is unfavorable for increasing the unit freeze-drying area and unit time production.
4, drying room pressure
The pressure in the drying chamber affects the rate of heat transfer and mass transfer. In terms of mass transfer, the lower the pressure, the better. 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 surface of the dry layer. It is necessary to increase the rate of water vapor escape in the dry layer. First, increase the temperature of the sublimation interface and increase the vapor pressure of the interface. It is to increase the vacuum of the drying chamber and reduce the vapor pressure on the surface of the drying layer.
5, heat transfer mode heat transfer mode
According to the traditional classification, it can be divided into: conduction, convection, heat radiation and medium heating (microwave heating). Since the sublimation drying process involves the transfer of heat and mass (water vapor), the heat transfer method is more effective in transferring the heat to the material, which has a greater influence on the drying rate.