Vapor Resistance Research Articles

The use of an internal airtight membrane in CLT external wall in terms of hygrothermal performance

This study focused on the dry-out capacity of the vapor-permeable CLT (cross-laminated timber) external wall and the impact of using an internal airtight membrane. The results of the work were obtained first from the field measurements, after which the simulation model was created and validated, and the hygrothermal performance of the wall was analyzed by a stochastic approach. The results of this showed that the CLT dries out quickly and safely in a wall assembly with a high water vapor permeability, even with the large range of initial CLT MC (13-25%). When an additional airtight layer with high vapor diffusion resistance (Sd of 244 m) is added between the insulation and the CLT, the dry-out capacity of the CLT decreases significantly and there is a high probability of mold growth on the CLT surface. The risk of mold growth can be prevented when the vapor resistance (Sd) of the airtight layer is reduced to 1.5 m in a case where initial CLT MC is up to 25% and in a case where initial MC is up to 20%, the vapor resistance of an airtight layer must be reduced to 3 m.

Study of hygroscopic behaviour of spruce during adsorption and desorption

Sorption of water vapour in hygroscopic porous materials is associated with latent heat release and absorption. This phenomenon should be taken into account to achieve a better understanding of the coupled transfer of vapour and heat in hygroscopic porous materials. In this paper, water vapour adsorption and desorption in the longitudinal direction of spruce samples are studied. Neutron radiography is used to measure changes in moisture content and wireless thermocouples are used to measure temperature changes. During the adsorption and desorption experiments, large changes in moisture content and temperature are observed. A hygrothermal model is developed to simulate vapour and heat transfer during adsorption and desorption experiments. Generally, the numerical model predicts well the measured moisture and temperature changes. The large moisture change is due to the low vapour resistance factor in the longitudinal direction of the spruce samples. The latent heat associated with vapour adsorption is the cause of the large temperature changes. It was found that vapour permeability affects both vapour and heat transfer, while thermal conductivity only affects heat transfer.

Moisture Vapor Permeability and Thermal Wear Comfort of Ecofriendly Fiber-Embedded Woven Fabrics for High-Performance Clothing.

This study examined the moisture vapor permeability and thermal wear comfort of ecofriendly fiber-embedded woven fabrics in terms of the yarn structure and the constituent fiber characteristics according to two measuring methods. The moisture vapor permeability measured using the upright cup (CaCl2) method (JIS L 1099A-1) was primarily dependent on the hygroscopicity of the ecofriendly constituent fibers in the yarns and partly influenced by the pore size in the fabric because of the yarn structure. On the other hand, the moisture vapor resistance measured using the sweating guarded hot plate method (ISO 11092) was governed mainly by the fabric pore size and partly by the hygroscopicity of the constituent ecofriendly fibers. The difference between the two measuring methods was attributed to the different mechanisms in the measuring method. The thermal conductivity as a measure of the thermal wear comfort of the composite yarn fabrics was governed primarily by the pore size in the fabric and partly by the thermal characteristics of the constituent fibers in the yarns. Lastly, considering market applications, the Coolmax®/Tencel sheath/core fabric appears useful for winter warm feeling clothing because of its the good breathability with low thermal conductivity. The bamboo and Coolmax®/bamboo fabrics are suitable for summer clothing with a cool feel because of their high thermal conductivity with good breathability. Overall, ecofriendly fibers (bamboo and Tencel) are of practical use for marketing environmentallyfriendly high-performance clothing.

Biobased Waterborne Polyurethane-Ureas Modified with POSS-OH for Fluorine-Free Hydrophobic Textile Coatings.

Waterborne polyurethane-urea dispersions (WPUD), which are based on fully biobased amorphous polyester polyol and isophorone diisocyanate (IPDI), have been successfully synthesized obtaining a finishing agent that provides textiles with an enhanced hydrophobicity and water column. Grafting of trans-cyclohexanediol isobutyl POSS (POSS-OH) to the biobased polymer backbone has also been investigated for the first time and its properties compared to a standard chain extender, 1,3-propanediol (PDO). The chemical structure of WPUD has been characterized by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The thermal properties have been evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Mechanical properties have been studied by tensile stress–strain analysis. Moreover, the particle size, particle size distribution (PSD), and stability of developed waterborne dispersions have been assessed by dynamic light scattering (DLS), Z-potential, storage aging tests, and accelerated aging tests by analytical centrifuge (LUM). Subsequently, selected fabrics have been face-coated by the WPUD using the knife coating method and their properties have been assessed by measuring the water contact angle (WCA), oil contact angle (OCA), water column, fabric stiffness, air permeability, and water vapor resistance (breathability). Finally, the surface morphology and elemental composition of uncoated and coated fabrics have been studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. All of the synthesized polyurethane-ureas provided the coated substrates with a remarkable hydrophobicity and water column, resulting in a more sustainable alternative to waterproof coatings based on fluoropolymers, such as PTFE. Grafting POSS-OH to the polymeric backbone has led to textile coatings with enhanced hydrophobicity, maintaining thermal, mechanical, and water column properties, giving rise to multifunctional coatings that are highly demanded in protective workwear and technical textiles.

Precision of Measurement of Water Vapor Resistance of Fabrics With Different Surface Roughness by a Skin Model

Skin models are used for determination of water and thermal resistance of fabrics. Measurement in these instruments starts with determination of water vapour resistance of a boundary layer above the sweating hotplate. In the second step, the hotplate is covered by the tested fabrics and the instrument measures WV resistance of the fabric and that of boundary layer. Afterwards, the difference between these measurements presents the required WV resistance of the measured fabric, provided that WV resistance of the boundary layer is in both measurements identical. However, fabric surface roughness may change WV resistance of the boundary layer in the second measurement. In the paper, the effect of the fabric surface on measurement precision is theoretically analyzed and experimentally verified by procedure, which provides same air surface friction during both steps of the measurement. Experiments confirmed certain but small effect of the fabric surface roughness on the measurement precision.

Moisture Vapor Resistance of Coated and Laminated Breathable Fabrics Using Evaporative Wet Heat Transfer Method

This study examined the effects of the fiber materials, fabric structural parameters, and surface modification method on the moisture vapor resistance of coated and laminated fabrics according to the measuring method in comparison with evaporative wet heat transfer method. The moisture vapor resistance (Ref) of the coated and laminated fabrics measured using evaporative wet heat transfer method was much more precise than water vapor transmission rate (WVTR) and water vapor permeability (WVP) measured using American Society for Testing and Materials (ASTM) and Japanese Industrial Standard (JIS) methods. The correlation coefficient between Ref and WVTR in the laminated and coated polyethylene terephthalate (PET) fabric specimens was the highest, i.e., −0.833, and −0.715, in coated fabric specimens. Hence, selecting an appropriate measuring method according to the fabric materials and surface modification method is very critical. According to curvilinear regression analysis, the influential factor affecting breathability of the PET fabric specimens measured using evaporative wet heat transfer method was fabric weight (R2 = 0.847) and fabric thickness (R2 = 0.872) in the laminated fabric specimens. Meanwhile, as per multiple linear regression, the most influential fabric structural parameters affecting the breathability of laminated fabric specimens measured using evaporative wet heat transfer method were the fabric density, weight/thickness, and weight followed by the fabric thickness (R2 = 0.943). These results would be valid for laminated breathable fabrics with characteristics within the range of this study and are of practical use for engineering laminated fabrics with high breathability.

Increased Comfort of Polyester Fabrics.

The hydrophilicity of fibers is directly related to the comfort of a fabric and represents one of the most important aspects of a textile. Therefore, polyester (PES) modification has focused on an increase in moisture content and a subsequent improvement of the user’s experience. Based on the glycerol hygroscopic properties, the main objective has been the enhancement of the hydrophilicity of polyester by glycerol treatments. Furthermore, microwave irradiation and alkaline treatment have been applied, in order to increase glycerol adhesion. Treated PES samples were characterized by performing moisture content, negative ion, water diffusion and water vapor resistance analyses. The effect of different treatment conditions such as bath ratio (1/10 or 1/15), temperature (40, 60 or 100 °C), time (2 or 5 min) and microwave radiation intensity (300 or 500 W) was evaluated. The moisture content of treated PES results indicated that by decreasing the bath ratio and increasing the time and temperature the moisture gain can reach almost 14%, which can be easily related to increases in the weight of the fiber. The treatment with alkali was done and led to the highest moisture increase. Treatment with 500 W microwave irradiation led to higher glycerol retention after rinsing. Different experimental conditions were applied to the glycerol-treated PES fabrics, and a clear improvement in moisture content was obtained increasing the comfort. The results were compared with the ones obtained for cotton and wool, where the moisture is higher than non treated PES.

Squarate-Calcium Metal–Organic Framework for Molecular Sieving of CO2 from Flue Gas with High Water Vapor Resistance

While molecular sieving is a desirable approach for extracting CO2 from flue gas, water vapor in the flue gas often poses significant difficulty in this separation process. To tackle this challenge, we targeted a squarate-calcium metal–organic framework with strong water stability, Ca(C4O4)(H2O), for its pore diameter was in the middle of the kinetic diameters of CO2 and N2. Ca(C4O4)(H2O) exhibited excellent separation performance for CO2/N2 (15/85 vol) with adsorption selectivity values of 73 at 1 bar and 298 K. This efficient separation was further confirmed by multicomponent breakthrough experiments. Additionally, Ca(C4O4)(H2O) showed strong interaction with CO2 based on the very high isosteric heat of 47.7 kJ/mol. The strong affinity between CO2 and Ca(C4O4)(H2O) was further explained with density functional theory calculations, which exhibited that CO2 was bound tightly via hydrogen bonds between the oxygen atoms in CO2 and the hydrogen atoms in H2O, as well as π–π interactions between CO2 and the aromatic ligand in the framework. Furthermore, the cyclic adsorption/regeneration experiments under 100% relative humidity, 15 vol % CO2, and balance N2 demonstrated that Ca(C4O4)(H2O) is a promising adsorbent for CO2 removal in practical applications due to its excellent tolerance to water vapor and recyclability.

Sodium alginate-based nanocomposite films with strong antioxidant and antibacterial properties enhanced by polyphenol-rich kiwi peel extracts bio-reduced silver nanoparticles

Sodium alginate (SA)-based films with excellent antioxidant and antibacterial activities were prepared, which was modified by polyphenol-rich kiwi peel extracts (PE) bio-reduced silver nanoparticles. In detail, PE was employed as reducing and capping agents to self-assemble silver@PE nanoparticles (Ag@PE NPs), which was further used to modify SA film in its functionality. In addition, the effects of the Ag@PE NPs amount on the physicochemical and biological performances were investigated. Results showed that SA-based films had strong tensile strength, water vapor resistance and good UV barrier properties. The incorporation of Ag@PE NPs drove a color change of SA-based films to redness and yellowness, while still showing good transparencies. Besides, Ag@PE NPs modified SA-based films showed a significant enhancement of antioxidant property, as well as an obvious improvement of antibacterial activity against Staphylococcus aureus and Escherichia coli. Therefore, this study provided a new insight for the reutilization of kiwi peels and a green, cheap and easy approach to prepare multifunctional SA-based food packaging films.

Effects of vapor duct thickness on the capillary blocking and thermal performance of ultra-thin vapor chambers under natural convection cooling

This work presents the performance test results for novel two-piece ultra-thin vapor chambers with a thickness (t) of 0.38 mm, 0.48 mm and 0.58 mm, having a vapor duct thickness (h) of 0.15 mm, 0.25 mm, and 0.35 mm, respectively. These ultra-thin vapor chambers simply comprise a top plate etched with arrayed pillars as the condenser and a mesh-wicked bottom plate as the evaporator and liquid path. The inner surface of the top plate contains cross parallel vapor ducts configured by aligned pillars for vapor spreading all over the vapor chamber. The pillars provide strong structural support, an enlarged condensation area, and a direct shortcut for liquid return. Compared to traditional vapor chambers, the novel ultra-thin vapor chambers have the advantages of simpler structure, easier manufacturing process, lower cost, superior anti-compression ability, and better thermal performance. They keep excellent structural integrity at a footprint of 140 mm × 80 mm. Cooled by natural convection, the vapor chamber resistances (Rvcs) are measured for different hs at different filling ratios (γs). Capillary blocking is observed for h = 0.15 mm and 0.25 mm at γ larger than 1.0, but it does not appear for h = 0.35 mm even with considerable over-charge. Although capillary blocking may slightly raise Rvcs, it can be avoided by suitable under-charging. Except for cases with significant over-charge, Rvcs are similar for h of 0.15 mm to 0.35 mm at heat loads less than 15 W due to the low vapor resistances at low mass flow rates. At heat loads of about 14 W, the minimum Rvcs of unblocked ultra-thin vapor chambers are about 0.25 K/W to 0.3 K/W, greatly superior to the value of 0.88 K/W of a 0.5 mm-thick copper plate.

Assessment of the Impact of Clothing Structures for Premature Babies on Biophysical Properties.

This article presents research on ergonomics and physiological comfort of protective clothing. Biophysical properties of selected three-layer textile assemblies that differ in geometry and raw material composition for the production of types of mummy sleeping bags for premature babies were investigated. The tests included measurements of air permeability, thermal resistance and water vapor resistance (both by means of human skin model), thermal insulation, and water vapor resistance (both using newborn manikin). Experimental research was supplemented by modeling the thermal insulation of the assemblies by designing their 3D models using selected CAD software and applying the finite volume method. The obtained results allowed the evaluation of the influence of different geometry and the raw material composition of the proposed assemblies on the performance parameters of protective clothing.

Effect of Lycra Weight Percent and Loop Length on Thermo-physiological Properties of Elastic Single Jersey Knitted Fabric

Abstract The aim of this work is to estimate the effect of loop length and Lycra weight percent (Lwp) on the geometrical and thermo-physiological comfort of elastic plain knitted fabric. Fifty single jersey knitted fabric samples were produced at five levels of Lycra weight percent (Lwp) (4%, 5%, 6%, 7%, and 8%) and loop length (2.7 mm, 2.9 mm, 3.1 mm, 3.3 mm, and 3.4 mm) with full plaited (fp) and half plaited (hp) of bare Lycra. The thermo-physiological comfort properties (thermal conductivity, absorptivity, and water vapor permeability), air permeability, and geometrical properties were measured at standard of each one. The results showed that the elastic single jersey knitted fabric thickness ranged between 3.12 times and 4.2 times of the yarn diameter (d). The fabric thickness increased when loop length is increased and decreased when Lwp is increased. The thermal conductivity, absorptivity, and water vapor resistance (WVR) decreased with Lwp increasing.

Sensing and Delineating Mixed-VOC Composition in the Air Using a Single Metal Oxide Sensor

Monitoring volatile organic compounds (VOCs) places a crucial role in environmental pollutants control and indoor air quality. In this study, a metal-oxide (MOx) sensor detector (used in a commercially available monitor) was employed to delineate the composition of air containing three common VOCs (ethanol, acetone, and hexane) under various concentrations. Experiments with a single component and double components were conducted to investigate how the solvents interact with the metal oxide sensor. The experimental results revealed that the affinity between VOC and sensor was in the following order: acetone > ethanol > n-hexane. A mathematical model was developed, based on the experimental findings and data analysis, to convert the output resistance value of the sensor into concentration values, which, in turn, can be used to calculate a VOC-based air quality index. Empirical equations were established based on inferences of vapour composition versus resistance trends, and on an approach of using original and diluted air samples to generate two sets of resistance data per sample. The calibration of numerous model parameters allowed matching simulated curves to measured data. Therefore, the predictive mathematical model enabled quantifying the total concentration of sensed VOCs, in addition to estimating the VOC composition. This first attempt to obtain semiquantitative data from a single MOx sensor, despite the remaining selectivity challenges, is aimed at expanding the capability of mobile air pollutants monitoring devices.

Design of sports-abaya and its thermal comfort evaluation

The market for sports-abaya in Saudi Arabia is growing due to an increasing participation rate of Islamic women in fitness and sports activities. As mandated by religious law, an abaya must be worn over daily clothes or sportswear by women in order to hide their body contour. The additional layer of the abaya will affect thermal comfort and performance of the wearer. Hence, a sports-abaya needs to be specifically designed to facilitate thermal comfort. This necessitates the selection and evaluation of fabrics appropriate for use in the production of sports-abaya. This study compared two fabrics (100% cotton knit and 100% polyester woven) for their air permeability, thermal resistance and evaporative resistance. The fabrics were then incorporated as sole variable into two models of sports-abaya. The thermal properties of these abayas were evaluated using a female thermal manikin in both standing and walking positions. Comparison was made with the results of a traditional abaya. The research work revealed that polyester woven fabric has a higher air permeability (44.9 mL/cm2/s) than cotton knitted fabric (24.1 mL/cm2/s). The vapor resistance of polyester fabric was lower than cotton fabric and their thermal resistant did not show any significant difference. Consequently, thermal manikin evaluation showed results favoring sports-abaya containing polyester fabric in both standing and walking positions. Furthermore, the thermal resistant and vapor resistant values of sports-abayas were lower compared with those of the traditional abaya. This leads to the conclusion that the newly designed sports-abaya containing 100% polyester woven fabric provides better thermal comfort than traditional abaya and sports-abaya containing 100% cotton fabric.

Mechanical and antimicrobial properties of high amylose corn starch/konjac glucomannan composite film enhanced by cinnamaldehyde/β-cyclodextrin complex

In the present research, cinnamaldehyde/β-cyclodextrin (CIN/β-CD) complex (0.5 %–3.0 %, w/v) were added into the composite film of high amylose corn starch (HAS) and konjac glucomannan (KGM) and the structural, physicochemical and bacteriostatic properties of the films were investigated. The results showed that the presence of CIN/β-CD complex decreased the crystallinity and short-range order structure of high amylose corn starch/konjac glucomannan (HAS/KGM) composite film. The CIN/β-CD complex also enhanced the polymeric interaction between the two polysaccharides, which improved the thermal ability of the composite film. The scanning electron microscopy (SEM) images showed compact and even surface and cross-section structure of the composite films when the complex addition was lower, while displayed heterogeneous aggregations of CIN/β-CD complex in the film with some pores after excessive addition of the complex. The mechanical strength of the film increased significantly from 14.51 MPa to 23.88 MPa and the water vapor resistance was improved due to the changes in skeleton structure of the composite film. The composite films exhibited obvious inhibition activity to Staphylococcus aureus and Escherichia coli, which displayed a promising application in food active packaging.

The effect of fabric’s structure on the breathability and the drying rate Properties

Many parameters affect sportswear comfort. Therefore, we selected five sportswear fabrics designed for jogging and hiking T-shirts to study their structural characteristics and to investigate the influence of these characteristics on the clothing comfort properties. The areal weight, the thickness, the loop length and the course and wales densities were calculated. Investigations were performed on air permeability, water vapor resistance and drying time/rate properties of selected fabrics. We found that an increase in the mass per square meter and in thickness decreases the air permeability and increases the water vapor resistance of knitted fabrics. The air permeability is proportional to the loop length, while the water vapor resistance is inversely proportional to the loop length. Finally we did not find any significant relation between the fabric’s structure characteristics and the drying time/rate.

Sensitivity analysis of transient heat and moisture transfer in a bio-based date palm concrete wall

Hygrothermal mathematical models are commonly used to describe heat and moisture transfer in porous and bio-based building construction materials. This allows to evaluate their thermal insulation capacity, as well as their ability to regulate external climatic conditions and ensure indoor comfort for inhabitants. In this paper, a sensitivity analysis is performed on Kunzel's model, while it is applied to simulate the hygrothermal behavior of a wall structure made of a new bio-based building material (cement composite including date palm fibers). In a first part, the effects of finite variations of material properties/boundary conditions on the model's outcome are investigated. In a second step, specific transfer modes are neglected in the model, in order to study their influence on the numerical predictions. The results of this parametric study show that special attention should be paid to few parameters (heat capacity and density for heat transfer, sorption isotherm and water vapor resistance factors for moisture transfer) at the expense of others. Uncertainties on these influent parameters may result in large error accumulation, especially when modeling the moisture transfer process. Furthermore, initial boundary conditions and sensors position appear to be possible sources of discrepancies in the calculated RH profiles. Finally, the pure conduction model is found to provide good estimation of the temperature profiles compared to the full model, whereas liquid transfer must always be taken into account in the model to ensure accurate RH predictions through a bio-based date palm concrete wall.

An advanced conduction based heat pipe model accounting for vapor pressure drop

Heat pipes are passive heat transfer devices which play an increasingly important role in state-of-the-art cooling solutions for various technologies like consumer electronics or electric machines. During design phase, reliable simulation results are the key for optimal performance and efficiency. In system level simulations, heat conduction models, characterized by low computational effort, are widely used to predict heat pipe thermal resistance. In order to accurately calculate overall thermal characteristics, a precise prediction of the vapor core’s temperature drop is crucial. In this study, a novel conduction-based method for calculating heat pipe performance is presented. Taking velocity components perpendicular to the main vapor flow into account, an analytic expression for calculating the axial pressure gradient is developed and validated through detailed CFD simulations. Assuming saturation conditions, results are used to determine the vapor core’s local effective thermal conductivity. Parameters needed for calculation are provided for both circular and flat heat pipes under various operating conditions. The final model accounts for phase change thermal resistance and temperature dependent fluid properties. The presented method yields significantly different results compared to state-of-the-art approaches in which thermal vapor resistance is either assumed to be zero or calculated assuming (Hagen-)Poiseuille flow. Simulation results suggest a strong dependence of vapor thermal resistance on evaporation and condensation mass fluxes, thermophysical fluid properties and local vapor temperature.

Numerical analysis on heat transfer characteristics of a multi-vapor channel vapor chamber with novel ultra-thin composite wick

A three-dimensional numerical model is established to predict heat transfer characteristics of a multi-vapor channel vapor chamber (VC) with novel composite wick. In order to validate the numerical model, the surface temperature of the VC is compared with the experimental results. The mass flow rate distribution of working fluid in the wick is obtained. And the effects of the height of the vapor channel on the velocity, pressure drop of the vapor and total thermal resistance are investigated at different heating powers. The velocity, pressure drop of the vapor and total thermal resistance have the same variation trend, which are all inversely correlated to the height of the vapor channel respectively. However, the reduction of the thermal resistance of the vapor decreases as the height of the vapor channel increase. At last, the conduction-based model for the vapor chamber is put forward and the effective thermal conductivity of the vapor channel is derived. The maximum relative error between the VC surface temperature prediction based on the conduction model and the experimental data is less than 5 %.

The Effect of Cement Addition on Water Vapour Resistance Factor of Rammed Earth.

The article aims to determine the effect of cement addition on the water vapour resistance factor of stabilized rammed earth. Literature analysis indicates that different earthen materials show large differences in water vapour resistance factor values. The high diffusion resistance of concrete concerning other construction materials suggests that cement will be one of the factors significantly affecting these values. The paper presents water vapour resistance factor test results of rammed earth with various soil particle sizes and cement contents. The obtained results showed that an increase of cement addition increases the diffusion resistance of the material. However, the diffusion resistance of cement stabilized rammed earth is still low compared to concrete.