How many hours to put the things freeze-dried freeze dryer?
Usually freeze-dried time need ten hours to 40 hours, different product freeze time.
Because the lyophilization process in fact is the heat transfer and mass transfer (
Water vapor)
At the same time, the process of heat transfer rate to affect the drying rate, thus affecting the lyophilization cycle, all the factors affecting heat and mass transfer will affect the drying rate, simple analysis is as follows:
1, the form and material components according to the freeze-dried form is usually divided into solid and liquid.
The morphology of solid and liquid concentration have bigger influence on the freeze drying rate.
2, precool rate which is formed by the freezing when the crystal size to a great extent, affect the drying rate and drying after the dissolution rate of the product.
And slow freezing process has the following difference: quick-frozen produce small ice crystals, slow frozen ice crystals is bigger.
Large ice crystals to sublimation, small ice crystals for sublimation, rapid freezing sublimation rate low, desorption rate.
Slow freezing sublimation rate, resolution rate is slow.
3, filling quantity
material during freeze-drying, packing into the container after there is the ratio of surface area and thickness of the material, i. e. freeze-dried related to the load.
Surface area, small thickness is beneficial to water distillation, easy to freeze and ideal quality.
Dry, unit area on the tray by dry wet heavy loads is an important factor to determine the drying time, under normal circumstances, the material accumulation is the more the thickness of the thin, the faster the heat transfer and mass transfer, the shorter the drying time.
However, freeze-dried material thickness thin, unit area less per batch drying of material, to improve the yield per unit freeze-dried area and per unit time.
4,
in drying chamber pressure in drying chamber pressure affect the rate of heat and mass transfer, in terms of mass transfer, the lower the pressure, the better, but for heat transfer, the higher the pressure, the better.
The size of the mass transfer rate, mainly composed of sublimation interface and dry layer on the surface of the temperature and pressure, to improve the escape rate of water vapor in dry layer, one is to improve the sublimation interface temperature, make interface vapor pressure increases;
The second is to improve the vacuum drying chamber, reduce dry layer on the surface of the vapor pressure.
5, heat transfer heat transfer according to the traditional classification can be divided into: conduction, convection and thermal radiation and heat medium (
Microwave heating)
。
As a result of the sublimation drying process involving heat and mass transfer,
Water vapor)
Pass, so, what methods of heat transfer through the heat more effectively to the materials, has a larger effect on the drying rate.
