Labconco FreeZone 6 Liter Benchtop Freeze Dry Systems 77520 Series - Manual (Page 6)

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Chapter 1: Introduction
ice and the heat removed from the collector to convert the water
vapor into ice.
Freeze Dry Rates
The efficiency of the freeze drying process is dependent upon the
surface area and the thickness of the sample, the collector
temperature and vacuum obtained, the eutectic point and solute
concentration of the sample. It is important to remember these
factors when trying to obtain efficient utilization of your freeze dry
system. A listing of selected materials and their approximate
drying times are shown in Table 1 for your reference.
SAFE TEMPERATURE AND DRYING TIMES
FOR SELECTED MATERIALS
Material
10mm Thick Safe
Temperature
°C
Collector
Temperature
°C
Hours
(Approx.)
Milk -5 -40 10
Urea -7 -40 10
Blood Plasma -10 to -25 -40 16
Serum -25 -40 18
Vaccinia -30 to -40 -50 22
Influenza Vaccine -30 -50 24
Human Tissue -30 to -40 -50 48
Vegetable Tissue -50 -80 60
*Total sample quantities are contingent on various freeze dryer capacities.
Up to the point of overloading the system, the greater the surface
area of the sample, the faster the rate of freeze drying. By contrast,
for a given surface area, the thicker the sample the slower the rate
of freeze drying. This is based on the fact that the heat of
sublimation is usually absorbed on one side of the frozen sample
and must travel through the frozen layer to vaporize water at the
other surface. In addition, as the sample is freeze dried, the water
vapor must travel through the layer of dried material. The thicker
the sample, the greater the chance that the dried layer may collapse
which would cause an additional decrease in the rate of freeze
drying.
The surface area and thickness of the sample can usually be
ignored when each sample contains only a few milliliters.
However, for larger volumes, the samples should be shell frozen to
maximize the surface area and minimize the thickness of the
Table 1