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

Abstract

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.