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should either break the boundary layer over the surface, or to minimize its
thickness. Thus, the material is dried under vacuum must be constantly heated.
Convection heating method in this case there is no, ie. A. At ambient pressure
reducing its thermal conductivity decreases. Thus, the necessity of combining
flows to vacuum drying al. Heating method. Heat can be transmitted contact,
radiation and dielectric methods. Transfer material with vacuum - dielectric
method allows for the opportunity to the fullest. At 0.01 MPa pressure medium
in the vacuum can only accommodate 68 g of water per 1m3.
Environment is completely saturated, and further the drying is terminated,
so the water vapor from the environment must be condensed and removed from
the chamber. For this purpose, they should be provided with a cooling system. It
is particularly important that the rate of condensation of steam within the
chamber is greater than or equal to the rate of evaporation of moisture.
According to the phase transitions "liquid - vapor - liquid" how much heat is
wasted through evaporation, the same must be removed from the cooling steam
condensation. Some growers mistakenly believe that all the moisture will
condense on the surface of the inner wall of the chamber, and the cooling system
do not. This leads to the termination of the drying process, or to an increase in its
length 2 - 3 times.
An effective way of preserving plant material is drying convective -
vacuum - impulse (CVI) exposure at which intensified external and internal heat
- and mass transfer, reduced processing time and eliminated the overheating of
products not only in the 1 - th period of drying, but after the removal of free
moisture . In pulsed evacuation preheated to the maximum allowable
temperature of the material arising due to strong pressure gradient dripping
process is enhanced 5-10 times of migration of the moisture to the surface of the
material to be dried and the drying wall chamber as a liquid phase transition in
the bypass steam inside the product. Active evaporation of moisture from the
surface of the product causes a reduction in its temperature. When the pulse
pressure changes in the drying chamber (. To Height = 100 Pa) in a pre-heated
raw material intensifies not only remove the moisture, and gases: oxygen from
voids and capillaries collapse of parts of intracellular membranes, resulting in
suppression of the oxidation - reduction reactions (killed of the bacteria), and as
a result of complex influence KVI - modes occur preservative effect. At KVI -
drying the maximum permissible temperature of heating of fruit, berries - no
more than 56 - 60, some flowers and herbs - not higher than 38 - 40, for
vegetables - 70 - 72 ° C. The heat input to the material produced by convection.
Duration CVI - drying a variety of plant materials is 40 - 90 minutes, the
process is conducted without overheating, with maximum preservation in food
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