Multilayer Fabric Systems Research Articles

An Extended Model for Analyzing the Heat Transfer in the Skin-Microenvironment-Fabric System during Firefighting.

This study proposed an extended multi-layer heat transfer model to simulate skin burns of firefighters during firefighting. The proposed model takes into account the effect of fabric movement frequencies, fabric movement amplitudes and human body movement speeds on the heat transfer between the skin and the heat source under low-level radiative exposure. The simulation performance was validated against the simulations in the published literature in terms of the heat transfer in the multi-layer fabric system, skin temperature and skin burns. The results indicated that the fabric periodic movement caused by human body movement decreased the time to skin burns and the skin temperature increased with increasing fabric movement amplitude. During firefighting, the time to 2nd degree burn was 33.3-35.2% shorter at medium human body movement speed than at low and high movement speeds. Furthermore, at low movement speeds, the time to 2nd degree burn was negatively associated with fabric movement amplitude, whereas it was delayed by 12.9-29.8% at the fabric movement amplitude of 2.5 mm at medium and high human body movement speeds. This research provides foundational knowledge for the development of a new generation of firefighters' protective clothing (FPC) and the assessment of skin burns in firefighters.

Effects of microencapsulated phase change materials on the thermal behavior of multilayer thermal protective clothing

Microencapsulated phase change materials (MPCMs) are increasingly seen as an adequate tool for heat management. The addition of a MPCM layer into a typical firefighters’ protective clothing can be used to mitigate burn injuries, increasing the time to second degree burns. A numerical approach is introduced to simulate the heat transfer in multilayer fabrics with MPCM. An overview of temperature field and total heat flux distribution for the multilayer fabric system with and without the MPCM is presented. Additionally, the effects of MPCM mass fraction, latent heat, specific heat and thickness are investigated to assess the thermal protective performance. The results demonstrate that the addition of a MPCM layer into the multilayer fabric assembly can be used to decrease the temperature obtained at the comfort liner boundary. Effect of heat intensity and radiation distance between the fabric system and heating source is also analyzed and discussed. The findings obtained in this study can provide some useful information on the beneficial design of clothing containing MPCMs.

Influence of surface polymer coating on ballistic impact response of multi-layered fabric composites: Experimental and numerical study

Composites based on aramid fibres are widely used to protect people and vehicles from high-velocity impact threats. Currently, quite a lot of attention is paid to methods for increasing the efficiency of such structures without a significant increase in areal density. The article demonstrates the results of experimental and computational studies of two types of multilayer fabric systems based on Twaron® 709. The first system consisted of dry fabric layers, and the second one was based on the fabric layers with polyvinyl acetate (PVA) surface coating. Experimental studies included quasi-static yarn pull-out tests, high-velocity impact tests of specimens without backing support, and tests on a plasticine block to assess the back face bulging. The results of the experiments showed that thin coatings of PVA contributed to a significant pull-out force increase due to polymer connections between the yarns. This effect led to the fact that specimens based on coated fabrics had a ballistic limit twice as much and showed a three-fold decrease in the depth of the dent on plasticine in comparison with dry fabrics. The total increase in surface density did not exceed 6% while maintaining high flexibility of the package. Also, numerical simulations were used to confirm the results of experiments. It was shown that mesoscale yarn-level models allow to predict plasticine indentation depths of the dry and coated multilayer fabric targets.

The approach of honeycomb sandwich structure for thermal protective clothing

In view of the cumbersome and sultry problem of thermal protective clothing, this study proposes a new method to optimum the protection and comfort properties of the multilayer fabric systems by changing the structure of a separate fabric layer. This research applied the honeycomb structure into thermal liner of multilayer fabric systems in thermal protective clothing. In the study, the experimental samples included 48 honeycomb sandwich structures and 4 traditional structures. A thermal protective performance tester was applied to measure the thermal protective performance provided by these fabric systems and the influence of honeycomb parameters on thermal performance was studied. The results show that the honeycomb sandwich structure fabric systems are lighter in weight and more comfortable to wear than traditional fabric systems. The core thickness plays a dominant role in the thermal protective performance of honeycomb sandwich structure fabric. Additionally, the honeycomb's side length and wall thickness both affected the thermal protection performance of the fabric system. Increasing wall thickness as well as decreasing the side length can improve the thermal protective performance of honeycomb sandwich structure fabric system. Finally, by comparing the thermal protection performance growth rate ratio, an optimal solution was found (core thickness: 2.04, side length: 2, and wall thickness: 7.8). Research on the thermal protection performance of honeycomb sandwich fabric systems helps to provide appropriate guidance to improve thermal protection and reduce heat burden by means of structural effects that affect heat transfer.

Effect of Air Gap Entrapped in Firefighter Protective Clothing on Thermal Resistance and Evaporative Resistance

Abstract Heat and water vapor transfer behavior of thermal protective clothing is greatly influenced by the air gap entrapped in multilayer fabric system. In this study, a sweating hot plate method was used to investigate the effect of air gap position and size on thermal resistance and evaporative resistance of firefighter clothing under a range of ambient temperature and humidity. Results indicated that the presence of air gap in multilayer fabric system decreased heat and water vapor transfer abilities under normal wear. Moreover, the air gap position slightly influenced the thermal and evaporative performances of the firefighter clothing. In this study, the multilayer fabric system obtained the highest thermal resistance, when the air space was located at position B. Furthermore, the effect of ambient temperature on heat and water vapor transfer properties of the multilayer fabric system was also investigated in the presence of a specific air gap. It was indicated that ambient temperature did not influence the evaporative resistance of thermal protective clothing. A thermographic image was used to test the surface temperature of multilayer fabric system when an air gap was incorporated. These results suggested that a certain air gap entrapped in thermal protective clothing system could affect wear comfort.

Quantitative assessment of the thermal stored energy in protective clothing under low-level radiant heat exposure

In addition to direct thermal energy from a heating source, a large amount of thermal energy stored in clothing will continuously discharge to the skin after exposure. Therefore, thermal protective clothing may have a dual effect on human skin in reality. An experimental investigation was conducted to study the energy storage within 15 different combinations of clothing layers exposed to low heat fluxes ranging from 2.5 kW/m2 to 8.5 kW/m2. The energy storage process, the distribution of energy storage, and variables critically impacting energy storage, including fabric layers, air gap under clothing, thermal resistance and heat source intensity were discussed. It is demonstrated that the weight and thickness of the fabric are dominating factors affecting energy storage. For a multilayer fabric system, 36–57% of the total amount of energy is stored in the outer shell. The neighboring layer proves to be very important for the energy storage in an individual fabric. The air gap that exists between the fabric and the skin exerts an influence on the energy storage within fabric layers. In addition, a linear correlation is observed between the energy storage and the total thermal resistance of a fabric system. The research findings will be brought to researchers to better understand the mechanism and factors associated with energy storage and help develop new fabric combinations in order to minimize heat transmission to the skin.

The effects of moisture on the thermal protective performance of firefighter protective clothing under medium intensity radiant exposure

Current firefighter protective clothing is composed of multilayer fabric systems. The outer shell fabrics inevitably become wet in the process of firefighters performing their duties, and sweat may also increase moisture in the inner layers of protective clothing. In this study, two kinds of outer shell fabrics (aramid IIIA fabric and aramid 1313 and flame-retardant viscose-blended fabric) and two kinds of thermal liner fabrics with different thicknesses were selected. Three wetness conditions were simulated for the outer shell fabric, thermal liner fabric and both fabrics together. A modified thermal protective performance (TPP) tester was applied to assess TPP provided by these wetted fabrics; in addition, second-degree skin burn time was predicted and absorbed energy indexes were calculated. The regression method was employed to create fitting curves for absorbed energy and second-degree burn time in different configurations and the Pearson correlation was established to analyze their relationship, in which the lowest R2 value could reach 0.9122 and p-values were all much less than 0.05. Performance results for both wet conditions indicated that outer shell moisture and a thicker thermal liner have a positive and increased negative effect, respectively, on fabric TPP. When the sample S-3-D (aramid 1313 and flame-retardant viscose-blended fabric, moisture barrier and the thin thermal liner) was both wetted in the outer shell and thermal liner, its second-degree burn time was improved by 12.8% over performance in dry conditions. These findings may have important applications for the design and manufacture of optimal protective performance clothing systems.

Numerical simulation of heat transfer in protective clothing with various heat exposure distances

This paper reports on a model of heat transfer through multi-layer firefighter protective clothing with an air gap under radiant heat flux of 8.5 kW/m2. The model considers the dynamical changes of heat exposure distance due to human body movement. The predictive results were found in good agreement with the experimental measurements. Numerical model was employed to study the effects of heat exposure distance and moving speed on heat transfer in multi-layer fabric system. The results showed that the heat exposure distance had an significant impact on skin burn. The safe zones for firefighting operation were more than 0.3 m for 2nd degree burn and 0.15 m for 3rd degree burn when the fabric system was exposed to 8.5 kW/m2 for 300 s. However, the moving speed could speed up the time to 2nd degree burn but alleviate the time to 3rd degree burn.

Development of a test device to characterize thermal protective performance of fabrics against hot steam and thermal radiation

Steam burns severely threaten the life of firefighters in the course of their fire-ground activities. The aim of this paper was to characterize thermal protective performance of flame-retardant fabrics exposed to hot steam and low-level thermal radiation. An improved testing apparatus based on ASTM F2731-11 was developed in order to simulate the routine fire-ground conditions by controlling steam pressure, flow rate and temperature of steam box. The thermal protective performance of single-layer and multi-layer fabric system with/without an air gap was studied based on the calibrated tester. It was indicated that the new testing apparatus effectively evaluated thermal properties of fabric in hot steam and thermal radiation. Hot steam significantly exacerbated the skin burn injuries while the condensed water on the skin’s surface contributed to cool down the skin tissues during the cooling. Also, the absorbed thermal energy during the exposure and the cooling was mainly determined by the fabric’s configuration, the air gap size, the exposure time and the existence of hot steam. The research provides a effective method to characterize the thermal protection of fabric in complex conditions, which will help in optimization of thermal protection performance of clothing and reduction of steam burn.

An improved model to analyze radiative heat transfer in flame-resistant fabrics exposed to low-level radiation

An improved heat transfer model, based on the two-flux model, in a multilayer flame-resistant fabric system with an air gap was proposed. The developed model considered the thermal radiation by absorbing, transmitting, emitting and reflecting in porous fabrics. The predicted results of the new model were compared with the previous Beer’s law model and the experimental results, and were found to be in good agreement with the experimental ones. The aim of this study is to investigate the mechanism of radiant heat transfer in the multilayer fabric system and the effects of the optical properties of flame-resistant fabric on heat transfer in the fabric system. The numerical results demonstrated that the self-emission in multilayer fabric system increases not only the rate of thermal energy transferred to human skin during thermal exposure, but also the rate of thermal energy transmitting to the ambience during cooling. The fabric’s optical properties have a complex influence on the transmitted and stored energy in multilayer protective clothing. The finding obtained in this study can provide references for the improvement of the thermal protective performance of flame-resistant fabrics.

The effect of moisture and air gap on the thermal protective performance of fabric assemblies used by wildland firefighters

The thermal protection performance (TPP) provided by fabric assemblies used by wildland firefighters is greatly affected by both the moisture and the air gap trapped in multilayer fabrics. In this paper, the effect of moisture, coupled with air gap on TPP was analyzed under radiant heat exposures of 21 kW/m2. The air gap sizes from 0 to 5.2 mm were analyzed using an air gap height regulation device; the moisture content of the multilayer fabric combinations around 0–70% were obtained by spraying distilled water to simulate varying amounts of sweat absorption. The results obtained indicate that certain air gaps entrapped in multilayer fabric system have a positive effect on TPP for both dry and wet multilayer fabric combinations. However, obvious trend changes in thermal protection were observed among dry and wet configurations when the air gap was moved to different positions. For the wet configurations, the second-degree burn time increased as the air gap moved further from the heat source, which was contrary to burn time response under dry conditions. These findings suggest that the complicated reciprocal effect of air gap and moisture on thermal protection should be both considered in analyzing the TPP of fabric assemblies.

Analyzing the transmitted and stored energy through multilayer protective fabric systems with various heat exposure time

The energy transmitted directly during thermal exposure as well as the stored energy that is continuously discharged from the heated fabrics after exposure can contribute to burn injuries. This study examined the effect of heat exposure time on the transmitted and the stored energy through multilayer protective fabric systems. The influences of the exposure duration on the amount of transmitted energy, the amount of stored energy, and also the action period of the stored energy release were discussed. A newly developed index was introduced to evaluate the thermal protection levels. The analyses demonstrated that the amount of transmitted energy increased continuously with an increase of exposure time; however, the amount of stored energy released to the sensor was limited in the process of exposure time increase. The maximum amount of stored energy was about 14.0 J/cm2 for the selected fabrics. As the exposure time was further increased the stored energy decreased to the range from 8.5 J/cm2 to 13.7 J/cm2. The grade of the thermal protection against a second-degree burn injury decreased with the increase of the exposure duration. By using the introduced index, the thermal performance estimate values could be determined, thus avoiding use of the iterative techniques suggested by ASTM F2703.

Quantitative investigation of air gaps entrapped in multilayer thermal protective clothing in low‐level radiation at the moisture condition

SummaryThe effects of air gaps entrapped within the multilayer protective clothing system on the thermal performance were studied during low‐level radiation (2–10 kW/m2). A bench‐scale apparatus was designed to produce the liquid droplets and simulate human sweat transferring through the multilayer fabric system. Two air gaps located between the outer shell and the moisture barrier (Gap A) and between the moisture barrier and the thermal liner (Gap B) were used with different gap sizes (0, 2, and 5 mm). The thermal resistance analysis for the heat transfer with a multilayer flat wall was used to interpret the effects of air gap. The results show that the total thermal resistance of a multilayer clothing system and the thermal resistances of the two air gaps are linearly related with the level of heat flux. It is also indicated that the air gap position affects the beneficial effect of the gap size. The effect of Gap B to improve the thermal performance is better than that of Gap A. Copyright © 2014 John Wiley & Sons, Ltd.

Moisture Permeability Test and Analysis of the Fire Taking Cotton Multilayer Fabric System

This article about the moisture permeability test system of fire taking five outer fabric and five kinds of multi-layer fabric. Screening of fire suit multi-layer fabrics system, the water vapor permeability and fabric structure parameters of correlation analysis. The experimental results showed that, 3 # multi-layer fabric system is the best choice of the fire fighting service; Fabric thickness and i the square meter gram weight is inversely proportional to the fabric moisture permeability relationship; For the effect of PTFE membrane laminated fabric to fabric itself can also through the amount of water vapor has certain influence. While ensuring waterproof, Moisture permeability fabric may be appropriate to increase the resistance, in order to protect the user's comfort.

Thermal insulations of multilayer clothing systems measured by a bench scale test in low level heat exposures

Purpose – The purpose of this paper is to measure the thermal insulation of protective clothing with multilayer gaps in low-level heat exposures. Design/methodology/approach – Nine different combinations of protective clothing systems with multiple air gaps are used to measure the thermal insulation by a self-designed bench-scale test apparatus in different levels of an external thermal radiation of 2-10 kW/m2. The outside and inside surface temperatures of each fabric layer are also measured to calculate the local thermal insulation of each fabric layer and each air gap. Findings – The results show that the total thermal insulation of protective clothing under thermal radiation is less than that in normal environments, and the exposed thermal radiation will worsen the total thermal insulation of the multilayer fabric systems. Air gap plays a positive role in the total thermal insulation, and thus provides the enhanced thermal protection. It is also suggested that the local resistance of the air gap closer to the external thermal radiation is more easily affected by the thermal radiation, due to the different heat transfer ways in the fabric system and the external thermal radiation. Originality/value – Effects of air gap on the thermal insulation of protective clothing, and contribution of the local thermal resistance of each fabric layer and each air gap to the total thermal insulation.

Assessment of the heat and moisture transfer in a multilayer protective fabric system under various ambient conditions

This study was conducted to investigate the effect of multilayer protective clothing on heat and moisture transport under various ambient conditions. By using the Human-Clothing-Environment simulator, a four-layered clothing system was exposed to a high rate of sweat pulse for a duration of 3 hours in seven different ambient conditions: extremely hot and humid (EH, 40℃, 90% relative humidity (RH)), extremely hot and dry (ED, 40℃, 30% RH), hot and humid (HH, 34℃, 75% RH), hot and dry (HD, 34℃, 30% RH), warm and dry (WD, 27℃, 30% RH), slightly cold (SC, –3℃, 20% RH) and cold (CO, –10℃, 20% RH). The temperature and RH in the microclimate were measured and the distribution of within layers was analyzed. Several dynamic stage changes of the microclimate were observed throughout the test. Variations in ambient condition have an effect on the microclimate and the distribution of moisture accumulated within layers. Heat and moisture transport through the clothing system would be influenced by the condensation within layers. In cold conditions, 80% of the moisture accumulated in the clothing system was located in the thermal liner and moisture barrier, whereas in other conditions, most of it was accumulated in the thermal liner.

An Engineering Approach for Assessment of Fabric Filterability

Multilayer technical fabrics are an important part of fibrous filters used in raw water filtration systems. The implementation of the filtration process depends on the structure of the fabric system, water particle deposition mechanisms and water flow conditions. This paper discusses, in terms of theoretical models, the results of an investigation on the flow resistance and efficiency of raw water filtration at the initial stage, in which the dispersed phase consists of liquid particles, through a multilayer technical fabric system with different structural parameters. The research results indicate the functional dependence of filtering properties on thestructural parameters of the fibres studied (primarily, fabric packing density coefficient,fabric tightness, and raw water flow parameters, such as the water flow rate (time)). The results of the research on multilayer technical fabrics with particular focus on the analysis of pore fraction distribution may be of crucial importance in forecasting the use of multilayer technical fabrics as filtering media for raw water filtration processing, considering that the conditions are sufficient

Effects of multiple air gaps on the thermal performance of firefighter protective clothing under low-level heat exposure

The thermal performance of firefighters' protective clothing entrapping multiple air gaps and exposed to low heat fluxes has been studied using a newly designed bench-scale test apparatus. Different air gap sizes (0, 2 and 5 mm), and entrapped positions within the multiple fabric system between the outer shell, the moisture barrier, and the thermal liner, respectively, were investigated at three levels of thermal radiation (2, 5 and 10 kW/m2) over a prolonged period. The effect of air gap size and its position on the heat transfer in a multilayer fabric system are interpreted in terms of a theoretical flat multi-wall structure. The results show that the thermal protective performance of a multilayer fabric system is reduced under low-level heat flux with and without an air gap. It is indicated that the time for skin to burn in direct contact with the inner layer is increased with the size of the air gap, due to an increase in the total thermal resistance of the fabric combination and a decrease in heat radiation between two adjacent fabric layers separated by an air gap. The results also provide an insight into the contribution of the thermal resistance of each fabric layer and each air gap to the overall protective effect of the clothing system. The difference in the received heat flux with different air gap sizes in different positions shows that the effect of air gap size is related to its position.

Air permeability of multilayer woven fabric systems

A model to predict the air permeability of a multilayer woven fabric system from the air permeability and construction parameters of a single fabric has been developed. A new factor to account for the distortion of the threads in the fabric due to the flow of air through the layers of the fabric is proposed. This model incorporates the fabric cover factor (determined using an image‐processing method) and the proposed distortion factor (determined based on yarn linear density and fabric structure). The performance of the proposed model has been successfully validated by using it to predict the air permeability of other multilayer woven fabric systems and comparing it to experimentally determined values. The model can thus be used as a valuable tool in the engineering design of multilayer woven structures with desired air permeability performance requirements.

The manufacture of microencapsulated phase change materials suitable for the design of thermally enhanced fabrics

Thermal comfort of a fabric is one of the important tasks of the designers that require an engineering approach. In this study, we first aimed to establish a manufacturing technique based on in situ polymerization in order to accomplish the microencapsulation of phase change materials (PCMs) that can ultimately be used in different textile applications, i.e. incorporating such products into the multi-component non-conventional fabrics. This method is suitable for the laboratory-scale work as well as the industrial-scale one, considering some important issues like energy and time savings. Four types of polyurea-formaldehyde microcapsules containing different waxes and a control group of 100% shell material were produced and then examined by DSC, particle size and SEM analyses. Furthermore, we also focused on the contributions of microencapsulated PCMs to the thermal performances of fabrics of certain passive insulation characteristics for the given cold weather and physical activity conditions, based on the model developed for a multi-layer fabric system.