Abstract
AbstractTheory is outlined relative to the effect of pressure on permeabilities and thermal conductivities of gases in porous solids in the slip flow and free‐molecule flow regions, and experimental results are reported for several freeze‐dried food materials. Mean pore diameters for the porous materials calculated from permeability data were about 100 μ and were in agreement with microscopic observations. Thermal conductivities followed the predicted behavior of a constant value at high pressures, with a gradual decrease to another constant value at very low pressures. The results show that the usual operating pressure range of freeze‐dryers (0.1 to 1.0 mm. Hg) corresponds to the transition region between slip flow and free‐molecule flow.
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