A revised multi-Fickian moisture transport model to describe non-Fickian effects in wood

Holzforschung ◽  
2007 ◽  
Vol 61 (5) ◽  
pp. 563-572 ◽  
Author(s):  
Henrik Lund Frandsen ◽  
Lars Damkilde ◽  
Staffan Svensson
Keyword(s):  
Diffusion Equation ◽  
Transport System ◽  
Moisture Transport ◽  
Transport Model ◽  
Bound Water ◽  
Anomalous Behavior ◽  
Adsorption Rate ◽  
Fickian Diffusion ◽  
Sorption Rate ◽  
Rate Model

Abstract 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.

Implementation of sorption hysteresis in multi-Fickian moisture transport

Holzforschung ◽  
2007 ◽  
Vol 61 (6) ◽  
pp. 693-701 ◽  
Author(s):  
Henrik Lund Frandsen ◽  
Staffan Svensson
Keyword(s):  
Moisture Content ◽  
Diffusion Equation ◽  
Moisture Transport ◽  
Bound Water ◽  
Water Concentration ◽  
Water Diffusion ◽  
Fickian Diffusion ◽  
Worst Case ◽  
Coupled Diffusion ◽  
Sorption Hysteresis

Abstract In the cellular structure of wood, bound-water diffusion and water-vapor diffusion interact via sorption in a complex moisture-transportation system. At low relative humidities, moisture transport may be modeled by a Fickian diffusion equation with a good approximation. At higher relative humidities, slow sorption and faster bound-water diffusion cause effects, which have been referred to as non-Fickian or anomalous, as they cannot be modeled by one Fickian diffusion equation. Previous research has demonstrated that a set of coupled diffusion equations, namely the multi-Fickian model, can represent this behavior. The multi-Fickian model describes the combined transport of bound water and vapor and their interaction through sorption. The bound-water concentration is also influenced by sorption hysteresis. In the worst case, sorption hysteresis may result in deviations of up to 30–35% in moisture content. Hence, for a precise moisture content computation, sorption hysteresis must be taken into account. The present paper explains the relation between sorption hysteresis and multi-Fickian moisture transport, and clarifies how models for the two phenomena are coupled. To illustrate the effects, a finite element simulation, which is based on the combined model, is presented.

Theoretical analysis of moisture transport in wood as an open porous hygroscopic material

Holzforschung ◽  
2011 ◽  
Vol 65 (1) ◽  
pp. 97-102 ◽  
Author(s):  
Tomaz Hozjan ◽  
Staffan Svensson
Keyword(s):  
Moisture Transport ◽  
Transport Model ◽  
Experimental Studies ◽  
Bound Water ◽  
Coupled Model ◽  
Moisture Sorption ◽  
Sensitivity Analyses ◽  
Coupled Processes ◽  
Model Parameters ◽  
Hygroscopic Material

Abstract Moisture transport in an open porous hygroscopic material such as wood is a complex system of coupled processes. For seasoned wood in natural climate three fully coupled processes active in the moisture transport are readily identified: (1) diffusion of vapor in pores; (2) phase change from one state to another, also called moisture sorption; and (3) diffusion of bound water in wood tissue (in the cell wall). A mathematical model for predicting moisture transport in wood for a given condition must at least consider the dominating active processes simultaneously to be considered accurate. In this study, a theoretical investigation is conducted on the influence of the model parameters on the model response to a known step change of ambient vapor pressure. The objective is twofold. First, to investigate if model simplification can be conducted in a transparent and stringent manner, not compromising required model accuracy and precision. Second, to show model characteristics that could enable tailored experimental studies to verify or discard variations of this type of transport model. The model sensitivity analyses clearly showed that there are large differences on the degree of influence of the three processes on the outcome of the coupled model. Least significant is the bound water diffusion. Based on the results from the sensitivity analyses, a simplified model for moisture transport in wood is proposed.

Moisture Transport in Wood-Based Structural Panels under Transient Hygroscopic Conditions

2020 ◽  
Vol 70 (3) ◽  
pp. 283-292
Author(s):  
Daniel Way ◽  
Frederick A. Kamke ◽  
Arijit Sinha
Keyword(s):  
Moisture Transport ◽  
Transport Model ◽  
Oriented Strand Board ◽  
Primary Objective ◽  
Accelerated Weathering ◽  
Wood Composite ◽  
Transport Parameters ◽  
Moisture Profile ◽  
Cyclic Changes ◽  
Wood Based Composite

Abstract Development of moisture gradients within wood and wood-based composites can result in irreversible moisture-induced damage. Accelerated weathering (AW), generally employing harsh environmental conditions, is a common tool for assessing moisture durability of wood composite products. Use of milder AW conditions, such as cyclic changes in relative humidity (RH), may be of interest to the wood-based composites industry in assessing moisture durability under more realistic conditions. The primary objective of this study was to determine whether moisture profile development in oriented strand board and plywood during cyclic RH changes could be reasonably predicted with a simple moisture transport model, which may be practical for wood-based composite industry members seeking to develop new AW protocols. The diffusion model based on Fick's second law with empirically determined moisture transport parameters fits the experimental data reasonably well for the purpose of screening RH parameters.

Moisture Transport Model for Enhancing FHWA HIPERPAV Predictions

2009 ◽  
Vol 2113 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Qinwu Xu ◽  
J. Mauricio Ruiz ◽  
George K. Chang ◽  
Robert O. Rasmussen ◽  
Dan K. Rozycki
Keyword(s):  
Moisture Transport ◽  
Transport Model

scholarly journals Numerical Solution for a Non-Fickian Diffusion in a Periodic Potential

2013 ◽  
Vol 13 (2) ◽  
pp. 502-525 ◽  
Author(s):  
Adérito Araújo ◽  
Amal K. Das ◽  
Cidália Neves ◽  
Ercília Sousa
Keyword(s):  
Diffusion Equation ◽  
Periodic Potential ◽  
Space Dimension ◽  
Numerical Solutions ◽  
Brownian Particle ◽  
Particle Density ◽  
Mean Square Displacement ◽  
Hyperbolic Type ◽  
Fickian Diffusion ◽  
Spatial Shape

AbstractNumerical solutions of a non-Fickian diffusion equation belonging to a hyperbolic type are presented in one space dimension. The Brownian particle modelled by this diffusion equation is subjected to a symmetric periodic potential whose spatial shape can be varied by a single parameter. We consider a numerical method which consists of applying Laplace transform in time; we then obtain an elliptic diffusion equation which is discretized using a finite difference method. We analyze some aspects of the convergence of the method. Numerical results for particle density, flux and mean-square-displacement (covering both inertial and diffusive regimes) are presented.

Influence of Cultivar on the Predictive Performance of a Moisture Transport Model Developed for Parboiled Paddy Drying

2013 ◽  
Vol 31 (5) ◽  
pp. 494-506 ◽  
Author(s):  
Lovelyn N. Onuoha ◽  
Ndubisi A. Aviara ◽  
Toyin A. Abdulrahim ◽  
Ahmed T. Suleiman
Keyword(s):  
Moisture Transport ◽  
Transport Model ◽  
Predictive Performance
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