A Model to Explain "Anomalous" Moisture Sorption in Wood Under Step Function Driving Forces


  • M. J. Cunningham


Diffusion, water vapor, cell walls, adsorption, non-Fickian behavior


It has been hypothesized that "anomalous" transient moisture sorption in wood at high relative humidities is due to slow sorption of moisture in the cell walls. A mathematical model describing this phenomenon has been developed, which fits well the two-stage sorption (Fickian and non-Fickian) visible in experimental data and uses parameters with clear physical meaning. The values of these parameters can be derived by simple means. Thickness effects and other non-Fickian behavior are examined.


Burch, D. M., and W. C. Thomas. 1991. An analysis of moisture accumulation in a wood frame wall subjected to winter climate. NISTIR 4674 National Institute of Standards and Technology, Gaithersburg, MD.nCarslaw, H. S., and J. C. Jaeger. 1959. Conduction of heat in solids. Oxford University Press, London, UK.nChristensen, G. 1960. Kinetics of water vapor sorption by wood, I. The effects of sample thickness. Austral. J. Appl. Sci. 11:294.nComstock, G. L. 1963. Moisture diffusion coefficients in wood as calculated from adsorption, desorption and steady state data. Forest Prod. J. 13(3):96.nCrank, J. 1975. The mathematics of diffusion. Oxford University Press, Oxford, UK.nCunningham, M. J. 1990. Modelling of moisture transfer in structures. II. A comparison of a numerical model, and analytical model and some experimental results. Bldg. Envir. 25:85.nCunningham, M. J. 1994. Modelling of moisture transfer in structures. Ill, A comparison between the numerical model SMAHT and field data. Bldg. Envir. 29:191.nHildebrand, F. B. 1956. Introduction to numerical analysis. McGraw-Hill, New York, NY.nKelly, M. W., and A. C. Hart. 1970. Water vapor sorption rates by wood cell walls. Wood Fiber 1(4):270.nKerestecioglu, A. A., and L. Gu. 1990. Theoretical and computational investigation of simultaneous heat and moisture transfer in buildings: "Evaporation and condensation" theory. ASHRAE Trans. 96(1):455.nKohonen, R. 1984. Transient analysis of the thermal and moisture physical behaviour of building constructions. Bldg. Envir. 19:1-11.nPedersen, C. R. 1990. Combined heat and moisture transfer in building constructions. Report No. 214. Thermal Insulation Laboratory, Technical University of Denmark, Lyngby, Denmark.nSkaar C., C. Prichananda, and R. Davidson. 1970. Some aspects of moisture sorption dynamics in wood. Wood Sci. 2(3):179.nWadsö, L. 1994. Unsteady-state water vapour adsorption in wood: An experimental study. Wood Fiber Sci. 6(1): 36.nYokota, T. 1959. Diffusion of sorption-water through the cell wall of wood. J. Japan Wood Res. Soc. 5:143.nYuill, G. K., and Assocs. 1990. Comparison of WALLDRY predictions with Atlantic Canada moisture test hut data. Canada Mortgage and Housing Corporation, Ottawa, Canada.n






Research Contributions