Freeze-dryer components

With freeze-dryers used in production and also with pilot plants, all the critical plant components should be supplied redundant to make sure that the process can be continued if there is a mechanical or electrical failure. Redundancy is particularly advisable in the following cases ... 

All freeze-dryers are constructed from the same basic components, even though they may vary greatly in size and appearance. 

Freeze drying Freeze drying of foods takes place in a freeze dryer at vacuum levels of 0.4 to 1.3 mbar absolute, corresponding to sublimation temperatures from -30 to -17°C depending on the product requirements. The main components of the freeze dryer are... 

All parts of the freeze-dryer that come in contact with solvent vapour must be solvent-resistant. The solvent blend must dissolve all components of the formula and should have its freezing point well above the shelf temperature of the freeze dryer. Blends of tert-butanol and chloroform (from 2 1 to 1 4 mixing ratio) are suited for most lipid blends. 

After the fractions have been collected, the solvent needs to be removed by using a freeze-dryer, rotary evaporator, or high-throughput parallel evaporator. Nonvolatile components can be removed with reversed-phase SPE procedures prior to solvent removal if the aqueous portion of the buffer is sufficiently large. 

The Conrad system [5] is a commonly used continuous freeze dryer for treating product in trays. The success of this type of plant is based on the simplicity and reliability of each component that goes to form the total system. The details of this and other continuous systems are given in Refs. [5,8]. 

Essential components of a freeze dryer include the vacuum chamber, condenser, and vacuum pump. As in other forms of drying, freeze-drying represents coupled heat and mass transfer. For the analysis of this operation, Karel [26]... 

Because the heat flux is not evenly distributed through the sublimation chamber, resulting principally from the relative importance of the radiative flux component coming from the shelves and from the side-walls of the freeze-dryer, each vial of the whole batch does not receive the same overall heat flux. In fact, it is well knovm that the vials located at the edges of each shelf present shorter sublimation and desorption times and higher temperature profiles. This phenomenon can be investigated by... 

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