A discussion of the effect of chamber pressure on heat and mass transfer in freeze-drying.

There have been many reports concerning the influence of chamber pressure on primary drying times and sublimation rates of freeze-dried materials. However, there is disagreement about the mechanisms responsible for the observed effects. The complex interaction between system parameters and product nature, which may lead to the contradictory views expressed in the literature, are discussed. In particular, it is considered by the present authors that results derived from pure ice are not applicable to product in which a cake of residual solids is formed.