Moisture Transport Behavior Research Articles

<p>Impact of Climate and Geographic Location on Moisture Transport in Wood Construction Walls and Implications for Selecting Vapor Retarders</p>

This research effort studied two similarly built homes in two different geographic locations in an attempt to demonstrate the affect that climatic conditions have on the selection and installation of appropriate vapor diffusion retarders to control moisture transport in wood-framed structures. Much misinformation and suppositions exist regarding which vapor diffusion retarder to use, where to place it within the structure, and whether it is even necessary. As a result, uncontrolled moisture transport is often a significant factor in the premature degradation of a structure; this also adds to poor indoor air quality resulting from the growth of mold and mildew. Nine climatic values of temperature, humidity, and air pressure were recorded at 20-30 minute intervals at various locations within the wall cavities and the outside of both test structures, for a 12-week period from January to March. These data allowed the researchers to perform calculations to predict the potential for growth of mold or mildew within the structure. Ultimately, these data were further compared for moisture transport behavior with the simulation software WUFI (“Wärme und Feuchtigkeit Instationären), a PC program developed by the Institute for Building Physics in Germany and the Oak Ridge National Laboratories in Tennessee for calculating coupled heat and moisture transfer in building components.

Prediction of transport properties of wood below the fiber saturation point – A multiscale homogenization approach and its experimental validation. Part II: Steady state moisture diffusion coefficient

In this publication a multiscale homogenization model for moisture transport in wood is developed and validated. The model aims at prediction of macroscopic transport properties of clear wood samples from their microstructure and the physical properties of a few microscale constituents. In the first part of this two-part paper, the theoretical background and fundamentals of the model were presented, and its specification for the estimation of macroscopic thermal conductivities was shown. In this second part the model is applied to steady state moisture diffusion below the fiber saturation point. The model starts on a scale of about 50 μm, where the wood cells form a honeycomb-like structure. In a first homogenization step the effective moisture transport behavior of the cell structure is determined from moisture diffusion properties of the cell walls and the (moist) air in lumens, respectively. Further homogenization steps account for the larger vessels that exist in hardwood species, the annual rings which are a succession of layers with different densities, and finally wood rays, that form pathways in the radial direction throughout the stem. The model validation rests on experiments as in the case of heat conduction: The macroscopic diffusion coefficients predicted by the multiscale homogenization model for tissue-specific composition data (input data set II) are compared to corresponding experimentally determined tissue-specific diffusion coefficients under steady state conditions (experimental data set). As for thermal conductivity, the good agreement of model predictions and test data underlines the suitability of the presented multiscale model.

Computational and Experimental Investigation of Moisture Transport of Spacer Fabrics

This paper investigates the moisture transfer behavior of spacer fabrics. Spacer structures are knitted fabric constructions comprising two separate fabrics which are joined together by spacer threads. In order to investigate the dynamic moisture transfer of spacer fabrics, an experimental apparatus was developed which made the simulation of human body sweating possible. In the experimental section, the influence of some parameters such as the kind of spacer threads and also heat setting under drawing on moisture transport properties is investigated. Heat setting under drawing affects air permeability, thickness and porosity of spacer fabrics. The Results showed that water vapor produced by sweating can be easily and quickly transferred from the skin to the outer surface to keep the skin dry. In the computational section, a mathematical model was developed to describe moisture transport behavior of spacer fabric. The model was in high good agreement with the observations in the experiments.

Alteration of the unsteady sorption behaviour of maple (Acer pseudoplatanus L.) and spruce (Picea abies (L.) Karst.) due to thermal modification

Abstract The aim of the present investigation was to evaluate the influence of a thermal modification on the kinetics of the water vapour sorption of maple (Acer pseudoplatanus L.) and spruce [Picea abies (L.) Karst.] based on the assumption that the Fickian equation can be applied in this regard in the first approximation. The unsteady-state sorption process between two equilibria of humidity was modelled as a diffusion process. The rate of sorption was recorded by the gravimetric method, and then the diffusion coefficient was determined through inverse parameter identification. The thermal modification leads to an alteration of the unsteady sorption behaviour of both wood species. Transport of water vapour decreases with increasing degree of modification. Depending on wood moisture, the trends of diffusion coefficients include all three levels of modification. Furthermore, the diffusion coefficients decrease when the thickness of specimens decreases. The calculated diffusion coefficients showed a length dependency both for unmodified and thermally modified spruce and maple. Accordingly, the results clearly show that these woods have a non-Fickian moisture transport behaviour. The results are nevertheless useful for comparative purposes.

水熱連成移動解析にもとづく高強度マスコンクリート中の温度及び湿度分布の予測

High strength concrete, which is characterized by a low water to cement ratio, has larger cement content than ordinary concrete. Even if die cross sectional area of reinforced concrete member is reduced on account of high strength, significant temperature rise at an early age can be observed. Additionally the low water to cement ratio leads autogenous shrinkage in the concrete. These phenomena may jeopardize durability and appearance of concrete members due to early age cracking. Regarding this problem, it is of vital importance to predict distribution and histories of temperature and moisture, which play important roles in early age cracking. In this research, based on the hydration model, heat and moisture transport behavior including latent phenomenon is modeled. And a potential of the proposed model is investigated with comparison of experimental data. As a result, it shows that the proposed model has a high potential to render the experimental data.

A new numerical implementation on 2D heat and moisture transfer through fabric

This paper presents a new algorithm to simulate 2D transient heat and moisture transport behavior through fabric. We established a 3D geometric fiber model first, and the fibers are anisotropic. The new model is deduced by the mass and energy conservation, capillary phenomenon. We use finite-difference time-domain to solve the partial differential equations. It describes the physical mechanisms of heat and moisture transfer in fabric, providing detailed information of the transferring process in fibrous media. The simulation results demonstrate that the new method is relatively accurate and easily implemented.

Moisture sorption and permeation in polyamide 6/clay nanocomposite films

AbstractThe moisture transport properties of a polyamide 6/clay nanocomposite have been studied through moisture sorption and permeation rate measurements. The temperature and concentration dependence of the steady state moisture uptake and permeation rate from the two types of experiment are distinctly different. The activation energy of moisture permeation obtained from the sorption experiment is lower than that derived from the permeation measurement. The interaction and contribution of the diffusion parameter and solubility parameter shows a complex moisture transport behavior in these nanocomposite films. Copyright © 2004 Society of Chemical Industry

Mathematical Simulation of Heat and Moisture Transfer in a Human-Clothing-Environment System

A mathematical model has been developed to describe the dynamic heat and moisture transport behavior of clothing and its interaction with the human thermoregulation system under transient wear conditions. A modification of Gagge's two-node model is used to simulate the human physiological regulatory responses. In clothing, heat and moisture transport is coupled with the sorption or desorption of water vapor in the fibers and the associated energy changes. If the physical activity and ambient conditions are specified, the model can predict the thermoregulatory responses of the body, to gether with the temperature and moisture profiles of the clothing. Experimental mea surements with garments made from fibers with different levels of hygroscopicity are compared with predictions by the model. There is good agreement between prediction and experiment for skin and fabric temperatures and the relative humidity of the cloth ing microclimate.