Modelisation of desorption isotherms and estimation of the thermophysic and thermodynamic properties of tropical woods in Cameroon : The case of Ayous and Ebony woods

A review at various models illustrates the necessary of choosing a model that
can best describe each wood in relation to its isotherms of desorption. The theoretical
models enable us to deduce several thermo physical parameters. The models of Dent and
G.A.B are quite appropriate in the evaluation of the isotherms of desorption of Ayous and
Ebony woods taking the humidity of the atmosphere air into consideration. The
parameters of Dent’s model vary favourably with regard to the theoretical precisions. The
level of humidity at fiber saturation points are at 0.2944 for Ayous wood and 0.19141 for
Ebony wood. The specific surface area occupied by the woods under study decreases
when there is a consequent increase in temperature. The specific surface area of Ayous
wood ranges between 295 and 162 m2/g whereas that of Ebony ranges between 183 and
96 m2/g, while the wood temperatures vary between 20 and 60°C. It is realised that, there
is a powerful relationship existing between the primary hydrophiles of Ebony and the first
layer of mater molecules. The desorption heat of multi layers of our woods are superior to
latent heat condensation of pure water. The heat condensation of water vapour constitutes
a specific given which is superior to the heat isosteric adsorption of the woods in
question. The soret effect is more important in the drying of Ayous wood than that of
Ebony. However, temperature does not influence the soret effect for Ebony wood, relative
air humidity is less than 0.85. This limits Ayous wood at 0.9. Above these limits soret
effect increases when there is an increase in atmospheric air temperature.

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