Summary
To predict the capillary transport of free liquid during the drying of softwood, it is essential to have knowledge of capillary pressure as a function of moisture content. The dependence of the capillary pressure on the wood's moisture content is predicted with a mechanistic model and measured for isothermal moisture movement in the tangetial direction. The experimental measurements confirm the model which is formulated on the postulate that the menisci that form between the liquid and gas in the tracheid lumens control the magnitude of the capillary pressure. Lumen size variation within an annual growh ring was found to significantly affect the local capillary pressure and indicated that separate flow paths are likely to exist in earlywood and latewood.
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Abbreviations
- C:
-
Concentration, g/cm3
- D:
-
Diffusion constant of proportionality (cm2/s)
- \(\vec g\) :
-
Gravitational acceleration (cm/s2)
- j:
-
Mass flux (g/s cm2)
- K:
-
Specific permeability (cm2)
- M:
-
Moisture content
- Pc :
-
Capillary pressure (dyne/cm2)
- Pg :
-
Gas phase pressure (dyne/cm2)
- P1 :
-
Liquid phase pressure (dyne/cm2)
- r:
-
Meniscus principle radius of curvature (cm)
- R:
-
Centrifuge radius of rotation (cm)
- S:
-
Saturation
- \(\vec v\) :
-
Velocity (cm/s)
- W:
-
Lumen width (cm)
- z:
-
Distance (cm)
- μ:
-
Dynamic viscosity (dyne s/cm2)
- ϱ:
-
Density (g/cm3)
- σ:
-
Surface tension (dyne/cm)
- ω:
-
Angular velocity (1/s)
References
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The authors wish to acknowledge the support of this work by the National Science Foundation under Grant No. CME-7906367. In addition, we must express our appreciation to the Weyerhaeuser Company for providing wood samples for the study and the Department of Agronomy and Soils at Washington State University for allowing us to use their gamma ray densitometry equipment. The comments by Professor J.F. Siau which led to producing a more readable manuscript are greatly appreciated
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Spolek, G.A., Plumb, O.A. Capillary pressure in softwoods. Wood Sci.Technol. 15, 189–199 (1981). https://doi.org/10.1007/BF00353471
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DOI: https://doi.org/10.1007/BF00353471