Moisture Adsorption and Transport by Wood Due to a Thermal Gradient Caused by Air-to-Air Thermal Differences
Keywords:Moisture movement, moisture profile, temperature gradient, concentration gradient, ceiling/partition separation
AbstractAn experiment was conducted in which a thermal gradient was established in wood by air-to-air temperature differences. A walnut board and a redwood board, each 3/4 inch thick and approximately 4 inches wide, were installed in a 1-inch-thick sheet of wood fiber insulation board employed as the lid of a chest-type freezer. The narrow edges of the boards were exposed to room air and freezer air, respectively. The MC profiles were periodically determined by removing cross sections from the boards and reducing them to thin slices. Moisture moved down the temperature gradient and against the concentration gradient. The average MC of the walnut and redwood boards increased 21% and 2%, respectively, during the 53-day test. The results showed that when wood is used as a thermal barrier, water vapor will enter the wood from the warm air and can be condensed in the wood if the necessary temperature profile exists. In certain applications of wood, this raises the possibility for free water accumulation in wood and the associated hazards. Moisture movement down a temperature gradient in wood is hypothesized to be a causative factor in the ceiling/partition separation problem with trusses in residential housing.
Bramhall, G. 1978. Sorption diffusion in the drying of solids. Fiber Sci. Technol. (11).nKoch, Peter. 1972. Utilization of the southern pines. Vol. 1. Agricultural Handbook No. 420.nMacLean, J. D. 1941. Thermal conductivity of wood. American Society of Heating and Ventilation Engineers. Journal Section, Heat, Piping and Air Conditioning.nSiau, John F. Nonisothermal moisture movement in wood. (Unpublished manuscript provided to the authors by Dr. Siau in July 1980.)nWengert, E. M. 1975. Prediction of moisture content in wood. Ph.D. Thesis. University of Wisconsin, Madison, WI.n
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