Technical data

2. General Information on Freeze
Drying
2.1. General Information on Freeze Drying
Freeze drying is the gentlest 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 dried
under vacuum without thawing. The ice condenser can also be
described as a vapor 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 vapor. 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 they are heatable. Once the “free water” has
been completely removed from the product, it is also possible to
remove the last traces of water bound by adsorption by means of a
very deep 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 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 bottles, etc.
• Pumps to evacuate air and water vapor
a) vacuum pump to evacuate the drying chamber
(= gas pump)
b) ice condenser with temperatures from -50°C to
-105°C (depending on the type of unit) to remove the
water vapor from the chamber
(= vapor pump)
Operating Manual Freeze Dryer ALPHA 1-4 LSC / ALPHA 2-4 LSC General Information on Freeze Drying • 9