An irreversible thermodynamics model for unsteady-state nonisothermal moisture diffusion in wood |
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Authors: | Dr S Avramidis Dr S G Hatzikiriakos Dr J F Siau |
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Institution: | (1) Department of Wood Science, University of British Columbia, V6T 1Z4 Vancouver, B.C., Canada;(2) Department of Chemical Engineering, University of British Columbia, V6T 1Z4 Vancouver, B.C., Canada;(3) P.O. Box 41, 12942 Keene, NY, USA |
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Abstract: | Summary A model that predicts heat and moisture transfer through wood in the hygroscopic range and which is based on the principles of irreversible thermodynamics, was evaluated with unsteady-state nonisothermal moisture desorption experimental data. The model predicted the phenomenon of thermal diffusion during the initial stages of desorption and results in a very good simulation of the desorption curve and the center's temperature change with time.Symbols Cp
specific heat of air (= 0.24 cal/g K @ 70 °C)
- CT
specific heat of wood, cal/g K
- D
transverse diffusion coefficient, cm2/s
- Eb
activation energy, cal/mol
- Eo
heat of vaporization, cal/mol
- EL
differential heat of sorption, cal/mol
- G
specific gravity of wood
- H
relative humidity, %
- hT
convective heat transfer coefficient, cal/cm2 s K
- hc
convective mass transfer coefficient based on the concentration of moisture in wood, cm/s
- hv
convective mass transfer coefficient based on the concentration of moisture in the air in equilibrium with the wood surface, cm/s
- KM
coefficient for diffusion due to moisture gradient, g/cm s %
- KT
transverse thermal conductivity coefficient, cal/cm K s
- M
moisture content, %
- Po
saturated vapor pressure, atm
- R
universal gas constant, cal/mol K (= 82.056 cm3 atm/mol K)
- t
time, s
- T
temperature, K
- x
distance, cm
Greek Letters
evaporation or condensation criterion
-
wood density, g/cm3
- W
water density (=1), g/cm3
- a
air density, g/cm3
Department of Wood Science and Forest Products Virginia Polytechnic Institute and State University Blackburg, Virginia 24061-0503 |
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