Combined Bound Water and Water Vapor Diffusion Into Sitka Spruce

The way in which water diffuses through wood is theoretically analyzed. Water vapor diffuses unhindered through the fiber cavities and pit chambers, but is hindered when diffusing through the permanent pit membrane pores. Bound water diffuses intermittently through pit membranes and the cell walls and continuously through the remainder of the wall. Coupling these facts with capillary structural data, a theoretical diffusion coefficient for the combined passage through the structure was calculated on the basis of combined paths in series and in parallel. The calculated value for an average moisture content of 20 percent is in good agreement with the measured values. These values show that in the pit system, the bound water diffusion through the pit membranes predominates in effect over the vapor diffusion through the permanent pit membrane pores, and also over the vapor diffusion through the pit chambers.

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