Abstract
The freeze-drying process is a complex heat and mass transfer process virtually. The drying process of freeze-drying is not only the key stage which decides the success of freeze-drying, but also the most difficult stage to control. There are lots of papers about heat and mass transfer in vacuum freeze drying at home and abroad. The present status of research on heat and mass transfer during vacuum freeze drying in the primary drying is summed up and analyzed, the trend of research in this field is discussed in this paper.
Highlights
In the freeze-drying process, the fresh materials or wet materials preprocessed in some way, are cooled until their temperature is lower than the the eutectic point and the internal moisture of the materials is fully frozen, forming solid ice
Because the change and move is under the condition of low temperature and low pressure, the basic principle of vacuum freeze-drying technology is heat and mass transfer mechanism at low temperature and low pressure [2]
In 1985, Millman and Liapis established unsteady heat and mass transfer model based on the energy balance and mass balance of frozen layer and the porous dried layer, and solve the one-dimensional desorption- sublimation model by a numerical method[10]
Summary
Vacuum freeze-drying technology, is called lyophilization. In the freeze-drying process, the fresh materials or wet materials preprocessed in some way, are cooled until their temperature is lower than the the eutectic point and the internal moisture of the materials is fully frozen, forming solid ice. In the desorption-sublimation model, Lifchied and Liapis thought that the ice sublimation in the frozen layer was simultaneous with the combined water desorption in the dried layer, and both the mass and the energy of water vapor were unchanged when through the porous dried layer.
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