Freeze drier condenser

Perform the vacuum leak test with an empty freeze drier and condenser. After reaching the maximum available vacuum, the vacuum pump is switched off after a delay time and the valves are closed. Monitor the vacuum decrease for a period of 24 h. Let the condenser cool to avoid water evaporation and vacuum decrease. 

In practice, at the beginning of the primary drying stage, more than 90% of the water in the initial solution has frozen. The ice is then removed by sublimation. Unlike the freezing process, ice sublimation is amenable to some measure of control. The heat flow to the ice front must be adjusted to balance exactly the heat absorbed by the sublimation of ice at the operating temperature of sublimation. In this chapter, we discuss the contributing mechanisms by which heat is transferred from the shelves of the freeze-drier to the ice front and the mechanisms by which water vapour is transferred to the condenser (mass transfer), and their relative contributions to the overall sublimation process. 

Figure 10.2 Freeze-drier illustrating the relative positions of external or internal water vapour condensers, (a) Freeze-drier with external water vapour condenser (b) freeze-drier with internal water vapour condenser.

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