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.

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.

scholarly journals Study on the Moisture Absorption and Thermal Properties of Hygroscopic Exothermic Fibers and Related Interactions with Water Molecules

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 98 ◽  
Author(s):  
Yi Cui ◽  
Shuyi Gao ◽  
Ruiyun Zhang ◽  
Longdi Cheng ◽  
Jianyong Yu
Keyword(s):  
Moisture Content ◽  
Thermal Performance ◽  
Water Sorption ◽  
Moisture Absorption ◽  
Bound Water ◽  
Absorption Process ◽  
Heating Performance ◽  
Hygroscopic Behavior ◽  
Water Sorption Capacity ◽  
Main Factor

The aim of this paper is to study the hygroscopic behavior of hygroscopic exothermic fiber-based materials and to obtain a better understanding of the thermal performance of these fibers during the moisture absorption process. The temperature distribution of different kinds of hygroscopic exothermic fibers in the process of moisture absorption, observed by infrared camera, demonstrated two types of heating performance of these fibers, which might be related to its hygroscopic behavior. Based on the sorption isotherms, a Guggenheim-Anderson-de Boer (GAB) multi-layer adsorption model was selected as the optimal moisture absorption fitting model to describe the moisture absorption process of these fibers, which illustrated that water sorption capacity and the water–fiber/water–water interaction had a significant influence on its heating performance. The net isosteric heats of sorption decreased with an increase of moisture content, which further explained the main factor affecting the heat dissipation of fibers under different moisture contents. The state of adsorbed water and water vapor interaction on the fiber surface were studied by simultaneous thermal analysis (TGA-DSC) measurement. The percentage of bound and unbound water formation at low and high humidity had a profound effect on the thermal performance of fibers. It can therefore be concluded that the content of tightly bound water a strong water–fiber interaction was the main factor affecting the heating performance of fibers at low moisture content, and the content of loosely bound water reflected that water sorption capacity was the main factor affecting the heating performance of fibers at high moisture content. This was further proven by the heat of desorption.

Dislocations in Norway spruce fibres and their effect on properties of pulp and paper

Holzforschung ◽  
2005 ◽  
Vol 59 (2) ◽  
pp. 163-169 ◽  
Author(s):  
Nasko Terziev ◽  
Geoffrey Daniel ◽  
Ann Marklund
Keyword(s):  
Mechanical Properties ◽  
Moisture Content ◽  
Norway Spruce ◽  
Juvenile Wood ◽  
Practical Importance ◽  
Pulp And Paper ◽  
Worst Case ◽  
Machine Failure ◽  
Wood Fibres ◽  
Control Samples

Abstract Wood “cell-wall deformation” is a comprehensive term describing any physical dislocation in the wall caused by mechanical forces. The development and effect of fibre dislocations on wood fibres, and their ultimate impact on the mechanical properties of paper remain rather obscure and controversial. Dislocations are difficult to quantify through a lack of defined measurable features, and research is aggravated by the inherent difficulties of applying statistical tools. A direct approach for studying the effect of dislocations on the mechanical properties of paper was used in this study. Dislocations in fibre cell walls were introduced by exposing whole wood fibres in mature and juvenile wood samples to compression stress. Sapwood samples of Norway spruce (Picea abies Karst.) were loaded by compression to their ultimate strength using an Alwetron-50 universal testing machine. Failure of samples conditioned to a moisture content of 9–15% always occurred in an oblique (relative to the fibre axis) plane and all fibres in the plane were deformed. When samples were loaded in a wet condition (i.e., moisture content close to the fibre saturation point), failure occurred at one end of the samples, resulting in highly disorganised fibres. Pulp and paper from the compressed fibres were produced and the mechanical properties of the paper were tested. Results of the mechanical tests were compared statistically to results derived from paper made from matched non-compressed control samples. Morphological features of fibres and dislocations after compression failure were characterised using microscopy (scanning electron microscopy, polarised light) on the whole wood and macerated fibres before and after paper testing. The above experimental approach showed that paper made from control samples had significantly better mechanical properties than paper made from samples loaded by compression under dry or wet conditions. At a tensile index of 90 N m/g, the tear index was measured as 23.6 mN m2/g for controls, while the corresponding values for compressed wet wood samples was 12.6 and 16.3 mN m2/g for samples at 9–15% moisture content. Paper made from juvenile wood also showed lower mechanical properties compared to controls. The results prove the negative effect of dislocations on the mechanical properties of paper in the worst case scenario and are of practical importance.

scholarly journals Measurement of leaf lamina moisture with a low-cost electrical humidity sensor: case study on a wheat water-mutant

2019 ◽  
Vol 19 (1) ◽  
Author(s):  
Agata Rascio ◽  
Michele Rinaldi ◽  
Giuditta De Santis ◽  
Nicola Pecchioni ◽  
Gabriele Palazzo ◽  
...  
Keyword(s):  
Moisture Content ◽  
Electrical Resistance ◽  
Low Cost ◽  
Bound Water ◽  
Genotypic Differences ◽  
Wild Type ◽  
Leaf Lamina ◽  
Mature Leaves ◽  
Moisture Meter

Abstract Background The presence and persistence of water on the leaf can affect crop performance and thus might be a relevant trait to select for or against in breeding programmes. Low-cost, rapid and relatively simple methods are of significant importance for screening of large populations of plants for moisture analysis of detached leaves. Leaf moisture can be detected using an electric circuit, where the resistance changes are proportional to the moisture of the measured surface. In this study, we present a protocol to analyse genotypic differences through the electrical properties of living or stored tissues, performed using a commercial device. Expanded and non-expanded leaves were compared to determine the effects of leaf maturity on these data. Two wheat genotypes that differ in tissue affinity for bound water were used to define the influence of water status. Results The device indirectly estimates leaf moisture content using two electrodes applied to the leaf lamina of fresh and stored samples. Single moisture readings using this moisture meter had mean execution time of ~ 1.0 min. Exponential associations provided good fits for relationships between the moisture meter reading (MMR) and the electrical resistance applied to the electrodes. MMR normalised for the water/ dry matter ratio (MMRnorm) was lower for mature leaves of the water-mutant than those of wild-type, for the fully hydrated fresh leaves. MMR of fully mature leaves when partially dehydrated and measured after 10 min at 27 °C and 40% relative humidity was greater for the water-mutant than the wild-type. Conclusions This case study provides a low-cost tool to compare electrical-resistance estimates of leaf moisture content, together with a promising and rapid phenotyping protocol for genotypic screening of wheat under standard environmental conditions. Measurement of changes in MMR with time, of fresh and partially dehydrated leaves, or of MMR normalised to tissue water content allowed for differentiation between the genotypes. Furthermore, the differences observed between genotypes that here relate particular to tissue affinity for bound water suggest that not only the free-water fraction, but also other water fractions, can affect these electrically estimated leaf moisture measures.

scholarly journals Moisture Absorption in Polymer Composites Reinforced with Vegetable Fiber: A Three-Dimensional Investigation via Langmuir Model

Polymers ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1847 ◽  
Author(s):  
Brito ◽  
Santos ◽  
Correia ◽  
Queiroz ◽  
Tavares ◽  
...  
Keyword(s):  
Moisture Content ◽  
Polymer Composites ◽  
Layer Thickness ◽  
Moisture Absorption ◽  
Three Dimensional ◽  
Water Concentration ◽  
Langmuir Model ◽  
Sisal Fiber ◽  
Average Moisture Content ◽  
Material Surface

This work aims to study numerically the moisture absorption in polymer composite reinforced with vegetable fibers using the Langmuir model which considers the existence of free and entrapped water molecules inside the material. A three-dimensional and transient modeling for describing the water absorption process inside the composite and its numerical solution via finite volume method were presented and discussed. Application has been made for polymer composites reinforced with sisal fiber. Emphasis was given to the effect of the layer thickness of fluid close to the wall of the composite in the progress of water migration. Results of the free and entrapped solute (water) concentration, local moisture content and average moisture content, at different times of process, and inside the composite were presented and analyzed. It was verified that concentration gradients of the molecules (free and entrapped) are higher in the material surface, at any time of the process, and concentration of free solute is greater than the concentration of entrapped solute. It was verified that the water layer thickness surrounding the composite strongly affects the moisture absorption rate.

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