Martin Christ Epsilon 2-10D LSCplus - Manual (Page 20)

Freeze-dryer EPSILON 2-10D LSCplus
2 Layout and mode of operation
20
Version 04/2013, Rev. 1.5 of 16/12/2014 • sb
Translation of the original operating manual
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2.2.2 Freeze-drying process
The main components of a freeze-dryer are:
• vacuum drying chamber with a temperature control system for adding
thermal energy
• vacuum pump for generating a vacuum inside the drying chamber
• ice condenser for binding the water vapour that is released by the
product.
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2.2.2.1 Preparation
The ice condenser chamber must be clean and dry. Any water residues
from a preceding drying run must be removed.
The media drain valve and the aeration valve must be closed.
In the case of units that are equipped with a pressure control valve
(standard on LSCplus units), the vacuum pump should be warmed up
(“warm-up”) for at least 15 minutes prior to the start of the main drying
phase. Do not subject the vacuum pump to condensable gases until the
operating temperature is reached. In this way, the service life of the
vacuum pump can be extended.
At the same time, the ice condenser is pre-cooled ("cool-down"). The ice
condenser temperature does not have any influence on the product
temperature. The sole purpose of the ice condenser is to bind the released
water vapour.
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2.2.2.2 Freezing
First, the product that is to be dried is frozen. This can be carried out either
directly in the freeze-dryer or in a separate deep-freeze. Especially in the
case of small filling quantities, we recommend pre-cooling the shelves as
well in order to prevent the product from thawing during the evacuation.
Two very different structures of the frozen material can be distinguished:
• crystalline structures with clearly distinguishable crystals
• amorphous structures with no crystal junctions at all (e.g. glass)
The majority of the freeze-drying products have a crystalline form.
When freezing these kinds of products, one must take into consideration
that too deep and too quick freezing leads to smaller ice crystals, which has
a negative effect on the duration of the drying process.
For every product to be dried, the solidification point must be determined as
a first step. This is the point at which the water that is contained in the
product has completely crystallised. In order to ensure an optimum freeze-
drying process, the product temperature should be approximately 10°C
below the solidification point.
A layer thickness of the product of 1-2 cm should not be exceeded, since
otherwise the drying duration would be negatively affected. If liquids are to
be dried in bottles with a layer thickness of more than 1 cm, we recommend
freezing them in a cooling bath with the aid of a shell or spin freezing
device (see figure). Due to the centrifugal force, the liquid to be frozen will
rise on the inner wall of the bottle and freeze. This procedure reduces the
layer thickness and, thereby, the total drying time will be shortened to a
considerable extent (see figures on the right side).