Theoretical Considerations in the Drying of Wood At Pressures Above Atmospheric

The drying of yellow poplar (Liriodendron tulipifera L.) specimens at pressures beyond atmospheric is described and the results compared with drying under atmospheric conditions. Results indicate that drying at pressures above atmospheric is characterized by a two-stage process compared to three stages for drying at atmospheric pressure. The absence of the linear or first stage in the drying process may have been caused by minor pressure disturbances. These disturbances may have permitted such rapid vaporization of free water that the rate of drying exceeded the rate at which free water could reach the surface of the specimen. It is also possible that pressure influenced the solubility of gases in water within the specimen. At times, drying at pressures above atmospheric increased volumetric shrinkage of the specimen, accompanied by collapse and honeycomb. These defects were most likely caused by a reduction in strength in the transverse direction due to higher temperatures within the sample. When collapse and honeycomb were not present, the radial and tangential shrinkage values were similar to those of specimens dried at atmospheric pressure.

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