1 Department of Civil Engineering, Technical University of Denmark 2 Section for Construction Materials, Department of Civil Engineering, Technical University of Denmark 3 Department of Energy Conversion and Storage, Technical University of Denmark 4 Aalborg University
This paper presents a study and a refinement of the sorption rate model in a so-called multi-Fickian or multi-phase model. This type of model describes the complex moisture transport system in wood, which consists of separate water vapor and bound-water diffusion interacting through sorption. At high relative humidities, the effect of this complex moisture transport system becomes apparent, and since a single Fickian diffusion equation fails to model the behavior, it has been referred to as non-Fickian or anomalous behavior. At low relative humidities, slow bound-water transport and fast sorption allow a simplification of the system to be modeled by a single Fickian diffusion equation. To determine the response of the system, the sorption rate model is essential. Here the function modeling the moisture-dependent adsorption rate is investigated based on existing experiments on thin wood specimens. In these specimens diffusion is shown to be negligible, allowing a separate study of the adsorption rate. The desorption rate has been observed to be slower at higher relative humidities as well, and an expression analogous to the adsorption rate model is proposed. Furthermore, the boundary conditions for the model are discussed, since discrepancies from corresponding models of moisture transport in paper products have been found. ©2007 by Walter de Gruyter.
Holzforschung, 2007, Vol 61, Issue 5, p. 563-572
Adsorption; Boundary conditions; Desorption; Diffusion; Multi-Fickian; Multi-phase; Non-Fickian; Slow sorption; Sorption rate
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