Multilayer Protective Clothing Research Articles

Assessment of Thermal Performance of Phase-Change Material-Based Multilayer Protective Clothing Exposed to Contact and Radiant Heat

The research presented in this article concerns the thermal properties of multilayer protective clothing, specifically, the impact of phase-change material (PCM) incorporation on the occurring heat transfer. Multilayer textile assemblies with PCM inserts (macrocapsules containing n-octadecane) and reference assemblies with PP inserts (macrogranules from polypropylene) with very similar geometry and the same textile layers were tested. The spatial geometry of tested assemblies was examined using high-resolution X-ray microtomography (micro-CT). The heating process of the assemblies was examined under the conditions of exposure to contact heat (using thermography) and radiant heat (using a copper plate calorimeter, according to EN ISO 6942). PCM-containing assemblies achieved a temperature rise of 12 °C in a longer period than the reference assemblies; for the contact heat method, the time was longer by 11 and 14 min, and for the radiant heat method by 1.7 and 2.1 min.

Modeling of Heat Transfer through Firefighters Multilayer Protective Clothing Using the Computational Fluid Dynamics Assisted by X-ray Microtomography and Thermography.

This paper explores the modeling of physical phenomena that occur in clothing that affect the safety and biophysical comfort of the user. Three-dimensional models of textile assemblies with complex morphology used in firefighters’ multilayer protective clothing were designed in a CAD environment. The main goal of the research was to design and experimentally verify (by thermography) the models in terms of simulations when the heat transfer occurs through them in selected ambient conditions using the finite volume method. The designed models took into account the subtle differences in the geometry of selected assemblies determined by high-resolution X-ray microtomography. The designed models made it possible to calculate heat transport with a difference of about 2% to 5% in comparison to experiment that depend on the ambient conditions and the complexity of the model geometry. Moreover, the comparison of the simulation results with the experimental outcomes shows that the mapping of subtle differences in the internal structure of the assemblies in the designed models allows us to observe differences in the modeled heat transfer.

Simulations of Heat Transfer through Multilayer Protective Clothing Exposed to Flame

Abstract In this paper, the safety and thermal comfort of protective clothing used by firefighters was analyzed. Three-dimensional geometry and morphology models of real multilayer assemblies used in thermal protective clothing were mapped by selected Computer-Aided Design (CAD) software. In the designed assembly models, different scales of the resolution were used for the particular layers – a homogenization for nonwoven fabrics model and designing the geometry of the individual yarns in the model of woven fabrics. Then, the finite volume method to simulate heat transfer through the assemblies caused by their exposure to the flame was applied. Finally, the simulation results with experimental measurements conducted according to the EN ISO 9151 were compared. Based on both the experimental and simulation results, parameters describing the tested clothing protective features directly affecting the firefighter’s safety were determined. As a result of the experiment and simulations, comparable values of these parameters were determined, which could show that used methods are an efficient tool in studying the thermal properties of multilayer protective clothing.

Analysis of the Thermal Insulation of Textiles Using Thermography and CFD Simulation Based on Micro-CT Models

Abstract The article presents the results of an attempt to use high-resolution X-ray micro-computed tomography (micro-CT) to model the thermal insulation of clothing as one of the most important parameters affecting the heat balance between a human and his/her surroundings. Cotton knitted fabric applied in functional clothing for newborns and aramid woven fabric used in multilayer protective clothing for firefighters were the tested materials. The 3D models of real textiles based on micro-CT images were developed. Next, the models were applied to heat transfer simulations using the finite volume method. The usefulness of the models was experimentally verified using thermography with real textiles. The simulation results were consistent with the measurement results and confirmed the relationship between the thermal insulation and geometry of the textiles on the one hand and the physical parameters of the raw materials from which they were made on the other hand.

Modeling of thermal performance of multilayer protective clothing exposed to radiant heat

Studies presented in this paper concern wide issue of thermal comfort of protective clothing. The Computer Aided Design (CAD) software tools to analyze thermal insulation of multilayer textile assembly used in thermal protective clothing were applied. First, 3D geometry and morphology of a real textile assembly was modeled. In the designed model different scales of resolution were used for individual layers, ranging from a homogenized nonwoven fabrics model to mapping the geometry of yarns in woven fabrics model. Next, the finite volume method to estimate thermal insulation properties of this assembly, when exposed to heat radiation, was used. Finally, the simulation results were verified experimentally using method described in EN ISO 6942. On the basis of both simulation and experimental results obtained for the multilayer textile assembly, protective clothing parameters directly affecting the ability to protect against heat, were determined. Correlating simulated and experimental values of these parameters were obtained, which may indicate that applied software can be an effective tool in analyzing thermal properties of newly designed multilayer functional clothing.

Modeling and analysis of the influence of the protective garment movement on the skin temperature and burn degree

A numerical thermal model of the multi-layer protective clothing which accounts for the clothing movement is presented. The model includes heat conduction and thermal radiation in non-grey fabrics and air gaps, diffusive transfer of water vapour through fabrics and air gaps, sorption and desorption of water in fabric fibers, non-equilibrium bio-heat transfer in the skin and perspiration on the skin surface. Moreover, the model contains infiltration of fresh air into the widest air gap between the clothing and skin due to the clothing movement. In the simulations the clothing was for a short time exposed to the radiative heat flux emitted from the external source and cooled down in the surroundings with its movement accounted for. The results obtained are used to assess the influence of frequency and amplitude of variation of the thickness of the widest air gap on the skin temperature and burn degree, heat fluxes and vapour mass flow rate on the skin surface as well as relative humidity close to the skin. Numerical simulations reveal that an increase in the movement frequency and amplitude results in a decrease of average values of the majority of monitored quantities on the skin surface or close to it. The most visible decreases are observed for the average skin surface temperature and values of the Henriques-Moritz integral.

Protective Clothing Based on High-temperature Thermal Radiation

Due to the needs of today's society, there must be a particular group of people working in a high-temperature thermal radiation environment. High-temperature environments can quickly cause significant harm to the human body, while thermal protective clothing can effectively reduce the harm to the human body caused by high temperatures. We can solve this problem by building a model. Set up a multi-layer protective clothing for heat conduction formula under the temperature variation of heat conduction model of the MATLAB to map the temperature with time, 3 d surface figure, the variation of the temperature distribution can lead the Excel data tables, and processing the data in the table data, using MATLAB software to curve fitting, the fitting curve of time and skin temperature. At the same time, on the optimal thickness of protective clothing, can be based on the initial conditions and boundary conditions, construct the objective function, and use the improved particle swarm algorithm for solving, specific calculation will difference algorithm as local search of particle swarm optimization algorithm, the particle swarm algorithm with differential evolution algorithm is the local optimization solution as the initial population of generation of differential evolution operations, thickness of solving it is concluded that the optimal approximate solution, and it is concluded that the optimal thickness. The convection and radiation heat transfer coefficients, convection and radiation heat transfer, and skin temperature were calculated. Then, by using the extensibility of CFD simulation and the flexibility of environmental temperature setting, the human thermal radiation stress response model was embedded into the CFD simulation, to predict the real-time changes of human core temperature in a high-temperature thermal radiation environment. Combined with the core temperature threshold and exposure time, people's rescue operation time under different thermal radiation environment conditions can be reasonably scheduled and arranged to reduce the level of thermal stress, improve rescue efficiency and guarantee people's life safety. Finally, the thermal protection clothing is studied to determine the temperature distribution of each layer of thermal protective clothing. It provides a theoretical reference for the functional design of thermal protective clothing.

Verification and validation of an advanced model of heat and mass transfer in the protective clothing

The paper presents verification and validation of an advanced numerical model of heat and moisture transfer in the multi-layer protective clothing and in components of the experimental stand subjected to either high surroundings temperature or high radiative heat flux emitted by hot objects. The developed model included conductive-radiative heat transfer in the hygroscopic porous fabrics and air gaps as well as conductive heat transfer in components of the stand. Additionally, water vapour diffusion in the pores and air spaces as well as phase transition of the bound water in the fabric fibres (sorption and desorption) were accounted for. All optical phenomena at internal or external walls were modelled and the thermal radiation was treated in the rigorous way, i.e., semi-transparent absorbing, emitting and scattering fabrics with the non-grey properties were assumed. The air was treated as transparent. Complex energy and mass balances as well as optical conditions at internal or external interfaces were formulated in order to find values of temperatures, vapour densities and radiation intensities at these interfaces. The obtained highly non-linear coupled system of discrete equations was solved by the Finite Volume based in-house iterative algorithm. The developed model passed discretisation convergence tests and was successfully verified against the results obtained applying commercial software for simplified cases. Then validation was carried out using experimental measurements collected during exposure of the protective clothing to high radiative heat flux emitted by the IR lamp. Satisfactory agreement of simulated and measured temporal variation of temperature at external and internal surfaces of the multi-layer clothing was attained.

Effect of moisture content on thermal protective performance of fabric assemblies by a stored energy approach under flash exposure

Firefighters wearing protective clothing perspire profusely in the process of performing their duties, and sweat increases moisture in the inner layers of multilayer protective clothing. Also, the outer shell fabrics inevitably become wet. In this study, two kinds of outer shell fabrics (aramid IIIA fabric and aramid 1313 and flame-retardant viscose-blended fabric) and three kinds of thermal liner fabrics with different thicknesses were selected. Two wetness conditions were investigated to simulate the sweating in thermal liner fabric with or without the wet outer shell fabric. A modified thermal protective performance (TPP) tester was employed to explore the effects of moisture and its distribution on stored thermal energy developed in six fabric systems and on TPP under flash exposure. Pearson correlations were established to analyze the relationships of the fabric systems’ thickness and second-degree burn time, and of absorbed energy and second-degree burn time in different configurations. The statistical analysis from these obtained data indicated that the thickness of fabric systems had no significant correlation for second-degree burn time ( p > 0.05), but the absorbed energy exhibited a strong relation (the lowest R2 value could reach 0.8070 and p-values were all much less than 0.05). Performance results for the wet thermal liner indicated that the negative impact on thermal protection reached the greatest degree in 15% wetness, but in some extreme situations (100% wetness), the performance was improved (the maximum increase can achieve 116.2% over performance in dry condition). However, the existing moisture in the outer shell showed a positive effect. These findings will enable the engineering of textile materials that achieve high performance protection from thermal hazards and give some guidance to firefighters during operations.

The effect of moisture content within multilayer protective clothing on protection from radiation and steam

The moisture from skin sweat and atmospheric water affects the thermal protective performance provided by multilayer protective clothing. Four levels of moisture content were selected to evaluate the impact of moisture on thermal protection under dry (thermal radiation) and wet (thermal radiation and low-pressure steam) heat exposure. Also, the role of moisture and its relationship with exposure time were analyzed based on skin heat flux and Henriques integral value. The addition of moisture to a fabric system was found to result in differences in second-degree and third-degree skin burn times. When moisture is added to a fabric system, it both acts as a thermal conductor to present a negative effect and provides a positive effect owing to thermal storage of water and evaporative heat loss. The positive or negative effects of moisture are mainly dependent on the thermal exposure time, the moisture content and the presence of hot steam.

Assessment of thermal performance of protective garments

PurposeThe paper aims to present the advanced mathematical and numerical models of conjugated heat and mass transfer in a multi-layer protective clothing, human skin and muscle subjected to incident external radiative heat flux.Design/methodology/approachThe garment was made of three layers of porous fabric separated by the air gaps, whereas in the tissue, four skin sublayers and muscle layer were distinguished. The mathematical model accounted for the coupled heat transfer by conduction and thermal radiation with the associated phase transition of the bound water in the fabric fibres and diffusion of the water vapour in the clothing layers and air gaps. The skin and muscle were modelled with two equation model which accounted for heat transfer in the tissue and arterial blood. Complex thermal and mass transfer conditions at the internal or external boundaries between the fabric layers, air gaps and skin were assumed. Special attention was paid to modelling of thermal radiation emitted by external heat source, for example, a fire, penetrating through the protective clothing and being absorbed by the skin and muscle.FindingsTemporal and spatial variations of temperature in the protective garment, skin and muscle, as well as volume fractions of the water vapour and bound water in the clothing, were calculated for various intensity of incident radiative heat flux. The results of numerical simulation were used to estimate the risk of the first-, second- and third-degree burns.Research limitations/implicationsBecause of the small thickness of the considered system in comparison to its lateral dimensions, the presented model was limited to 1D heat and moisture transfer. The convective heat transfer through the clothing was neglected.Practical implicationsThe model may be applied for design of the new protective clothing and for assessment of thermal performance of the various types of protective garments. Additionally, the proposed approach may be used in the medicine for estimation of degree of thermal destruction of the tissue during treatment of burns.Originality/valueThe novel advanced thermal model of the multi-layer protective garment, skin and muscle layer was developed. For the first time, non-grey optical properties and various optical phenomena at the internal or external boundaries between the fabric layers, air gaps and skin were accounted for during simulation of thermal interactions between the external heat source (e.g. a fire), protective clothing and human skin.

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.

A model of heat transfer in firefighting protective clothing during compression after radiant heat exposure

This paper presents an experiment-based, multi-medium heat transfer model to study thermal responses of multi-layer protective clothing with an air gap exposed to thermal radiation and hot contact surface. The model considers the dynamical changes of air gap, each layer’s fabric thickness, and air content contained in the fabric due to the pressure applied. The fabric heat transfer model developed from this study was incorporated into a human skin burn model in order to predict skin burn injuries. The predicted results from the model were well in agreement with the experimental results. A parametric study was conducted using various contact temperatures and applied pressures and design variables of firefighting protective clothing, such as physical properties of fabric layers and air gap sizes. It was concluded from the parametric study that resistance to transmission of injurious levels of heat decreases as the test temperature and contact pressure increase, and the contact heat transfer can weaken the importance of air gap under radiant heat flux(8.5 kW/m2) for 60 s and compression (pressure: 3 kPa, temperature: 316℃) for 60 s. The findings obtained in this study can be used to engineer fabric systems that provide better protection for contact heat exposure.

Analysis of Influence of Different Heat Transfer Modes on Temperature Distribution in the Protective Clothing and Skin

Analyses of influence of different heat transfer modes on temperature distributions in the firefighter's multi-layer protective clothing, skin and muscle were carried out. The system under consideration was irradiated from an external source of thermal radiation and consisted of several fabrics separated by thin air gaps and the tissue made of several sublayers. Simulations were performed by applying the in-house 1D numerical model which accounted for coupled heat conduction and thermal radiation in the protective clothing with the associated phase transition of the bound water in fabric fibers and diffusion of water vapor in fabrics and air spaces as well as for heat conduction, thermal radiation and blood flow in the tissue. Complex thermal and mass transfer conditions at the internal and external boundaries were proposed. Special attention was paid to modelling of non-grey thermal radiation penetrating the clothing and being absorbed by the tissue. The results obtained were used to estimate influence of different heat transfer modes present in the system, on temperature distribution in the clothing and tissue and on variation of times needed to reach the I, II and III degree burns.

Numerical modelling of transient heat and moisture transport in protective clothing

The paper presents a complex model of heat and mass transfer in a multi-layer protective clothing exposed to a flash fire and interacting with the human skin. The clothing was made of porous fabric layers separated by air gaps. The fabrics contained bound water in the fibres and moist air in the pores. The moist air was also present in the gaps between fabric layers or internal fabric layer and the skin. Three skin sublayers were considered. The model accounted for coupled heat transfer by conduction, thermal radiation and associated with diffusion of water vapour in the clothing layers and air gaps. Heat exchange due to phase transition of the bound water were also included in the model. Complex thermal and mass transfer conditions at internal or external boundaries between fabric layers and air gaps as well as air gap and skin were assumed. Special attention was paid to modelling of thermal radiation which was coming from the fire, penetrated through protective clothing and absorbed by the skin. For the first time non-grey properties as well as optical phenomena at internal or external boundaries between fabric layers and air gaps as well as air gap and skin were accounted for. A series of numerical simulations were carried out and the risk of heat injures was estimated.

Modeling the transmitted and stored energy in multilayer protective clothing under low-level radiant exposure

A finite difference model was introduced to simulate the transmitted and stored energy in firefighters' protective clothing exposed to low-level thermal radiation. The model domain consists of a three-layer fire-resistant fabric system (outer shell, moisture barrier, and thermal liner), the human skin, and the air gap between clothing and the skin. The model accounted for the relationship between the transmitted heat during the exposure and the discharged heat during the cooling-down period. The numerical model predictions were compared with experimental data. Additionally, the parameters that affect the transmitted and stored energy of protective clothing were investigated. The results demonstrate that for the typical multilayer firefighter protective clothing, the transmitted heat during exposure and the discharged heat after exposure totally determine the skin burn under low-level heat exposure, especially for third-degree skin burns. The findings obtained in this study can be used to engineer fabric systems that provide better protection for the stored thermal burn.

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.

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.

Study of heat transfer through multilayer protective clothing at low-level thermal radiation

The goal of this research is to develop a mathematical model of heat transfer in protective garments exposed to routine fire environment (low level of radiant heat flux) in order to establish systematic basis for engineering materials and garments for optimum thermal protective performance and comfort. In the first stage, this paper focuses on the formulation of heat transfer model suitable for predicting temperature and heat flux in firefighter protective clothing, using COMSOL Multiphysics® package based on the finite element method. Computational results show the time variation of the temperature at the inner face of the protective clothing system during the exposure to a low-radiant heat flux as well as during the cooling-down period. Model predictions of the temperature agreed very well with the experimental temperature. In the second stage of this study, in order to predict the first and second-degree burns, the model of heat transfer through multilayer protective system was coupled with the heat transfer model in the skin. The Pennes model was used to model heat transfer in the living tissue. The duration of exposure during which the garment protects the firefighter from getting first and second-degree burns is numerically predicted using Henriques equation. The results demonstrated that even for a low-level thermal radiant heat flux, a typical three-layer thermal protective clothing system is required to protect the wearer from skin burn injury.

Analyzing stored thermal energy and thermal protective performance of clothing

Protective clothing can store large amounts of energy when exposed to thermal (heat, flame) hazards. After exposure, the stored thermal energy discharges naturally—or may be forced if the clothing is compressed suddenly—and contributes to human skin burn injuries. In this study, the stored thermal energy that develops in thermal protective clothing materials was analyzed under different conditions. A stored energy approach that accounts for the thermal energy contained in the exposed test specimen is developed. The stored energy approach measures the total energy delivered to the sensor from a combination of the energy directly transmitted during exposure and the energy stored in the fabric system that is subsequently discharged after the thermal exposure. The study examines the effects of moisture on protective performance and the influence of air gaps between the fabrics and the sensor in terms of a stored energy approach and TPP/RPP (thermal protective performance/radiant protective performance) approach. A minimum exposure time that caused a prediction of a second degree burn was introduced and its contribution to burn injury was examined. These analyses demonstrate that the stored thermal energy obtained during thermal exposure is significant for multilayer protective clothing. Stored thermal energy contributes a large part of the total energy required to cause a second degree skin burn injury. The results indicate that, in cases of thermal exposure, stored thermal energy can reduce significantly the level of protection expected from wearing protective clothing.