Addenda Nota
Bulk Drying, General Rules
As the interface separating the dried and frozen
regions increases, the frozen portion of the matrix moves toward
the lower surface of the frozen material. This upper dry layer
is highly insulating to heat flux, but is less sensitive at
low pressures to the phenomena of mass transfer (pressure difference
between product and condenser induced by a temperature differential).
Heat transfer is increased by a pressure rise,
but at the expense of an increased resistance to mass transfer.
Water vapor migrating through the upper surface
of the matrix and the thermal conductivity of the ice layer
is two times higher than that of the dry layer.
In this condition, water vapor flux is decreased
as pressure is increased.
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