Decompression drying of Pinus radiata sapwood chips

Gas bubble nucleation and expansion in supersaturated aqueous solution, by decompression of the applied gas pressure, can remove free water from the cell lumens of a permeable wood structure. Carbon dioxide and nitrogen gas were used to evaluate the relative effects of the process variables pressure, temperature, and absorption time on the decompression drying of radiata pine sapwood chips. Water loss with carbon dioxide gas increased with pressure and absorption time, and varied with temperature. The volume of gas bubbles generated on decompression appeared to be an important criterion for water loss. The water loss also increased with repeated cycles of gas absorption and decompression drying, which suggests the proportion of air/water vapor present in the wood was also important in determining the amount of water loss. Water loss with nitrogen gas was determined by the number of cycles of decompression drying, rather than the period of nitrogen gas absorption. The very low solubility of nitrogen gas in water suggests the water loss occurred due to the compression and expansion of pre-existing air bubbles.

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