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Transport in Porous Media

, Volume 7, Issue 1, pp 39–61 | Cite as

A two-dimensional study of wood plank drying. The effect of gaseous pressure below boiling point

  • N. Ouelhazi
  • G. Arnaud
  • J. P. Fohr
Article

Abstract

This study is specially focused on the internal gaseous pressure of a plank of softwood, during drying below boiling point.

The one-dimensional numerical study shows a depression inside the plank, which depends on permeability and initial saturation. With the two-dimensional numerical study, one notices a reduction in this depression. As the longitudinal permeability is much greater than the transversal one (radial or tangential), the air flow can more easily fill the water volume evacuated. The simulation exhibits displacement of drying fronts from the transversal faces and extremities. As the exchange area of the extremities is weak, the two-dimensional effect is limited to a specific distance. The coefficients of the model are issued from literature.

An experimental study confirms the progression of the moisture field. The moisture profiles are obtained by conductivity measurements between needles. The improvement of two-dimensional drying can be evaluated using drying kinetics.

Key words

Wood drying one- and two-dimensional simulation gaseous pressure relative permeabilities experimental moisture profiles drying rate 

Nomenclature

Cp

massic heat at constant pressure (J/Kg.K)

D

diffusion coefficient (m2/s)

h

heat transfer coefficient (W/m2.K)

hs

differential heat of sorption (J/kg)

k

mass transfer coefficient (m/s)

K

permeability (m2)

Kr

relative permeability

\(\begin{gathered} \;^\circ \hfill \\ {\bar m} \hfill \\ \end{gathered} \)

rate of evaporation (kg/m3.s)

P

pressure (Pa)

R

perfect gas constant

rH

relative humidity of the drying air

T

temperature (K)

t

time (s)

V

velocity (m/s)

X

moisture content (dry basis)

x, y

coordinates

Greek Letters

δhv

latent heat of vaporization (J/kg)

λ

thermal conductivity (W/m.K)

Μ

dynamic viscosity (Pa.s)

ρ

volumetric mass (kg/m3)

Subscripts

a

dry air

b

bound water

c

capillary

eff

effective

g

gas(air+vapour)

l

liquid

s

solid

v

vapour

vs

vapour saturation

Superscripts

-

average value

g

intrinsic average over the gaseous phase

l

intrinsic average over the liquid phase

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References

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Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • N. Ouelhazi
    • 1
  • G. Arnaud
    • 1
  • J. P. Fohr
    • 1
  1. 1.Laboratoire d'Etudes Thermiques (UA CNRS 1403)Université de PoitiersPoitiersFrance

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