Longitudinal Diffusion and Permeability of Nonpolar Gases in Eastern Hemlock

Longitudinal ethane diffusion and nitrogen permeability were measured in oven-dry eastern hemlock sapwood. Samples were selected from 2 trees, 3 heights, and 4 quadrants, and either air- or solvent-dried for aspirated or unaspirated conditions. An IR method was used to detect ethane concentration in nitrogen at 25 C from which diffusion coefficients were calculated. The mean diffusion coefficient of the solvent-dried samples was 40% of free diffusion; the air-dried coefficient was about 16% of the free diffusion coefficient. No significant differences were found between position in the tree or oven-dry density and the diffusion coefficients. Diffusion coefficients were used to determine tortuosity differences in air- and solvent-dried wood. Effective pore openings obtained from permeability measurements, the Klinkenberg equation, and the temperature coefficient of diffusion confirmed that diffusion was occurring in the Kundsen end of the slip-flow region. A linear relationship was found between the permeability constant and diffusion coefficient. Diffusion and permeability measurements produce separate and complementary data that can be used to determine the mode of conductivity of gases in wood