On the Uncertainty of a Mathematical Model for Drying of a Wood Particle

Abstract

The reliability of the predictions of a mathematical model is a prerequisite to employ it. The drying process of a pine wood particle is modeled using a quasi-continuous multiphase porous media model. Different values and expressions from the literature of nine physical properties and transport coefficients are listed in this study. Lower and upper bounds of these model variables are determined and applied to the model, and a bounded output of the model is calculated. This study shows that taking arbitrary values of the model variables from the literature may lead to approximately 16 times differences in the calculated drying time of a single wood particle. By global sensitivity analysis, the most effective variables are determined. The variations of the coefficients of water vapor transport, except gas relative permeability, have a high impact on the presented drying model. For reliability of the predictions of the drying model, at least the values of the gas intrinsic permeability and water vapor diffusivity as well as capillary pressure have to be determined by own measurements in the studied conditions. One can use any of the reported values or expressions of effective thermal conductivity and specific heat capacity of wood as well as gas relative permeability and bound water diffusivity for modeling drying processes of wood particles, because all of them produce similar model predictions.

Modelling of intermittent microwave convective drying: parameter sensitivity

“…The results were similar to those in reference [23]. The temperature and vapour pressure were approximately the same.…”

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“…Where is the overall heat of the reaction. In the most general case, the transport terms are implemented in the conservative form, so the energy conservation equation takes into account the heat transfer through conductive, convective and diffusion transport [52,54,55]. Some authors apply simplifications in defining the transport, by omitting the heat transported through diffusion, assuming that the amount of heat exchanged through this phenomenon is negligible [28,[56][57][58].…”

“…Where < > is the equilibrium vapour density, < > is the water vapour density at a given time and is the time it takes to reach equilibrium between the actual vapour density and theoretically assumed saturation vapour density ("equilibration time"). Jahili et al [54] stated that the equilibration time has to be appropriately short in relation to the pore diameter of wood and proposed a constant value of 10 -5 s. Lu et al [65] proposed a correlation of the equilibration time based on particle specific surface area and pore diameter, expressed as:…”

“…The bound water's density increases at lower moisture content, according to the cell wall binding strength per amount of available water molecules [80]. In order to avoid over-complexity of the problem, authors typically use a constant value of 1000 kg/m 3 for the true density of the bound water [52,54,57,64,65].…”

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