Unified and heterogeneous modelling of water vapour sorption in wood

A. Tekleyohannes1 and S. Avramidis2

1Ethiopian Institute of Agricultural Research, Ethiopia
2University of British Columbia, Canada

Keywords: moisture sorption, self-organizing criticality, allometric scaling
property: molecular adsorption
material: wood

The first objective of this study was to develop a heterogeneous sorption model for earlywood, latewood and annual rings by taking into consideration a unified complex interaction of anatomy, chemical composition and thermodynamic parameters. The second objective was to upscale the annual ring level model to gross wood by applying artificial neural networks (ANNs) modeling tools using dimensionally reduced inputs through dimensional analysis and genetic algorithms. Four novel physical models, namely, dynamical two-level systems (TLS) model of annual rings, sorption kinetics , sorption isotherms and TLS model of physical properties and chemical composition were derived from first principles and successfully validated. The TLS model of annual rings is able to generate novel universal physical quantities, namely, golden ring volume (GRV) and golden ring cube (GRC) to which the sorption properties are very sensitive and also a new heterogeneity test criterion (HTC). The TLS sorption models revealed new evidence showing a transient nature of sorption hysteresis in wood in which the boundary sorption isotherms asymptotically converged to a single isotherm at large time limit. A novel method for the computation of internal specific surface area of wood was successfully validated using the TLS model of sorption isotherms. The fibre saturation point prediction of the model was also found to agree well with earlier reports. The TLS model of physical properties and chemical composition was able to reveal the self-organization in wood that gives rise to universal allometric scaling in wood. The dynamical TLS modeling revealed existence of self-organizing criticality (SOC) in wood in general and demonstrated mechanisms by which it is generated. Ten categories of unified ANNs gross wood sorption models that predict equilibrium moisture content, diffusion and surface emission coefficients were successfully developed and validated using anatomical, physical and chemical composition parameters which are generated using the four novel TLS models. The unique attribute of this study is the development of ANNs sorption prediction models from chemical composition, densitometry data of annual rings and thermodynamic variables with coarse-graining to gross wood level by revealing and explaining the complex nonlinear physical mechanisms at each level.

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