Martin Christ Alpha 2-4 LDplus - Manual (Page 15)

Operating Manual Freeze Dryer ALPHA 1-4 LDplus / ALPHA 2-4 LDplus General Information on Freeze-drying 15
2. General Information on
Freeze-drying
2.1. General Information on Freeze-drying
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 2 and unheatable shelves for drying in dishes
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)
b) ice condenser with temperatures from -50°C to
-105°C (depending on type of unit) to remove the
water vapour from the chamber
(= vapour pump)
2 Heatable (controlled) shelves are only possible with an LSC control system.