As for the structural principle and application characteristics of the freeze dryer, we must have known very well, but its speed influencing factors in the use process and the overall maintenance may not be clear. Beijing Songyuan Huaxing Technology Development Co., Ltd. sorted out the following knowledge points, let's have a look.

The whole process of freeze-drying is actually a process of heat and mass transfer (steam) at the same time. The transfer rate of heat and mass jointly affects the drying rate, thus affecting the whole freeze-drying cycle. All factors affecting heat and mass transfer will affect the drying rate

1. Material form and composition

According to the form of freeze-dried materials, they are usually divided into solid and liquid. The form of solid and concentration of liquid have great influence on freeze-drying rate.

2. Pre freezing rate

The crystal size formed during freezing greatly affects the drying rate and the dissolution rate of dried products. There are the following differences between quick freezing and slow freezing: the ice crystals produced by quick freezing are smaller than those produced by slow freezing. Large ice crystals are beneficial 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 fast sublimation rate and slow resolution rate.

3. Loading capacity

There is a certain ratio between surface area and material thickness when materials are sub packed into containers, that is, freeze-drying is related to the loading capacity. Small surface area and thickness are conducive to water sublimation, easy freeze-drying and good quality. In general, the thinner the thickness of the material, the faster the heat and mass transfer speed, and the shorter the drying time. However, if the material thickness is thin, there are less materials per batch per unit freeze-drying area, which is unfavorable to the improvement of unit freeze-drying area and unit time production.

4. Pressure in drying chamber

In terms of mass transfer, the lower the pressure is, 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 drying layer. In order to increase the water vapor escape rate of the drying layer, one is to increase the temperature of the sublimation interface to increase the water vapor pressure at the interface; the other is to increase the vacuum degree of the drying chamber and reduce the vapor pressure on the surface of the drying layer.

5. Heat transfer mode

According to the traditional classification can be divided into: conduction, convection, thermal radiation and medium heating (microwave heating). Because the sublimation drying process involves the transfer of heat and mass (water vapor), which heat transfer method is more effective to transfer heat to materials has a greater impact on the drying rate.