Movement of Moisture Through a Softwood in the Hygroscopic Range

A series of experiments have been designed to investigate the mechanism and the rate of moisture movement through a typical softwood in the hygroscopic range of wood moisture content. The object of this research was to investigate the mechanism of moisture movement by evaluating the bound water moisture conductivity coefficient at various moisture contents and temperatures. In order to do this, the coefficient, the product, and the sorption isotherm must be determined. A determination of these points was made with the following conclusions: l) Calculations of the values of the bound water diffusion coefficient in the cell wall of wood from experimental data indicate that their orders of magnitude are in agreement with the values obtained by Stamm, who used different experimental techniques. However, the effect of temperature was not as pronounced as found by Stamm. 2) The experimentally determined contributions of the bound water and vapor movement mechanisms in the wood varied with moisture content, temperature, and structural directions of movement. The bound water fraction was highest for radial movement and least for longitudinal movement. 3) The transverse and longitudinal diffusion coefficients as measured by the unsteady-state three-dimensional adsorption experiment were found to be dependent on temperature and moisture content, but their values were lower than expected.

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