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2.2. Preparation
2.3. Freezing
12 • General Information on Freeze Drying
In case the unit is equipped with a pressure control valve the
vacuum pump should be warmed up. The operation temperature
should be reached before loading the vacuum pump with condensable
gases. In this way, the service life of the vacuum pump can be
considerably extended.
The vacuum pump can be operated already during the freezing
process when the pressure control valve is closed. The vacuum pump
should be warmed up for at least 15 minutes or it should be switched
on at least 15 minutes before starting the main drying process.
It may occur that the vacuum in the ice condenser chamber or in the
drying chamber goes up during the main drying process (e.g. from
0.63 mbar to 0.47 mbar) although the valve to the vacuum pump is
closed. This can be explained physically by the pumping effect of the
ice condenser ("Cryo Pumping Effect").
Small product quantities are frozen directly inside the ice condenser
chamber of the freeze dryer. Larger quantities are pre-frozen in a
deep-freeze.
If liquids are to be dried in bottles with a layer thickness of more than
1 cm we recommend that pre-freezing is carried out with a shell or
spin freezing device in a cooling bath (see picture). Due to the
centrifugal force the liquid to be frozen will rise on the wall of the bottle
and freeze. With this freezing process the layer thickness is reduced
and thus the total drying period is shortened considerably.
Operating Manual Freeze Dryer ALPHA 1-2 LDplus
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