General Information On Freeze Drying - Fisher ALPHA 1-2 LDplus Operating Manual

2. General Information on Freeze
Drying

2.1. General Information on Freeze Drying

2
Heatable (controlled) shelves are only possible with an LSC control system.
Operating Manual Freeze Dryer ALPHA 1-2 LDplus
Freeze drying is the most gentle process for drying products. It is
based on the physical phenomenon of sublimation i.e. the direct
conversion from solid to gaseous state. The frozen product is placed
in the vacuum drying chamber for drying. The ice condenser can also
be described as a vapour pump as the moisture which evaporates
under vacuum during drying freezes onto the ice condenser.
Consequently the vacuum pump is only intended to remove the air
from the drying chamber (=gas pump) but not the vapour. In order to
start the sublimation process, energy must be supplied to the product.
This takes place during drying in round bottom flasks or wide-neck
filter bottles etc. due to the much warmer environment (direct heat
contact), on unheated shelves by means of heat radiation from the
environment and directly by means of the shelves when heatable.
Once the "free water" has been removed from the product, it is also
possible to remove the marginally contained adsorptively bound water
by means of very low vacuum. This part of the drying process is
referred to as final drying (desorption).
The main components of a freeze dryer are :
Vacuum drying chamber with heating device
a) heatable
b) shelves with sealing device for drying in bottles
c) rubber valves for connecting round bottom flasks,
wide-neck filter bottles, etc.
d) manifold for connecting round bottom flasks, wide-,
neck filter bottles, etc.
Pumps to evacuate air and water vapour
a) vacuum pump to evacuate the drying chamber
(= gas pump)
2
and unheatable shelves for drying in dishes
General Information on Freeze Drying • 9