A New Method for Separating Diffusion Coefficient and Surface Emission Coefficient
Keywords:
Diffusion coefficient, diffusion equation, lumber-drying curve, moisture concentration, moisture in wood, surface emission coefficientAbstract
An analytical procedure has been developed to separate the diffusion and surface emission coefficients in Newman's solution of the unsteady-state diffusion equation from a single lumber-drying curve. Previous methods required two to four drying curves corresponding to as many specimen thicknesses to achieve the same purpose. The new procedure reduces the experimental effort by 50% and more. The separation of the two coefficients will make it possible to study the dependence of diffusion coefficient on moisture concentration and that of surface emission coefficient on viscosity and velocity of airflow in any specified drying environment. Numerical examples are included to demonstrate the application of the new technique.References
Biggerstaff, T. 1965. Drying diffusion coefficient in wood as affected by temperature. Forest Prod. J. 15(3): 127-133.nChoong, E. T., and P. J. Fogg. 1968. Moisture movement in six wood species. Forest Prod. J. 18(5): 66-70.nChoong, E. T., and C. Skaar. 1969. Separating internal and external resistance to moisture removal in wood drying. Wood Sci. 1(4): 200-202.nChoong, E. T., and C. Skaar. 1972. Diffusivity and surface emissivity in wood drying. Wood Fiber 4(2): 80-86.nComstock, G. L. 1963. Moisture diffusion coefficients in wood as calculated from adsorption, desorption, and steady-state data. Forest Prod. J. 13(3): 97-103.nCrank, J. 1975. The mathematics of diffusion. 2nd ed., Clarendon Press, Oxford, London. Pp. 48, 239-243.nMcNamara, W. S., and C. A. Hart. 1971. An analysis of interval and average diffusion coefficients for unsteady-state movement of moisture in wood. Wood Sci. 4(1): 37-45.nNewman, A. B. 1931. The drying of porous solids: Diffusion and surface emission equations. Trans. Am. Inst. Chem. Engr. 27: 203-216.nRohsenow, W. M., and H. Choi. 1961. Heat, mass, and momentum transfer. Prentice-Hall, Inc., p. 385.nRosen, H. N. 1978. The influence of external resistance on moisture adsorption rates in wood. Wood Fiber 10(3): 218-228.nRosen, H. N. 1982a. Predicting wood surface moisture content during water vapor sorption. Wood Sci. 14(3): 134-137.nRosen, H. N. 1982b. Functional relations and approximation techniques for characterizing wood drying curves. Wood Sci. 15(1): 49-55.nSkaar, C. 1954. Analysis of methods for determining the coefficient of moisture diffusion in wood. J. Forest Prod. Res. Soc. 4(6): 403-410.nSkaar, C. 1987. Private Communication.n
Downloads
Published
Issue
Section
License
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.
