Search results

1 – 10 of over 13000
To view the access options for this content please click here
Article

Piotr Lapka, Piotr Furmanski and Tomasz Wisniewski

The 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…

Abstract

Purpose

The 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/approach

The 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.

Findings

Temporal 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/implications

Because 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 implications

The 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/value

The 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.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

Philipp Kölsch

The surface temperature of the sub-roof beneath the ventilation layer and the tiles is one of the most important factors for the hygrothermal performance of pitched roofs…

Abstract

Purpose

The surface temperature of the sub-roof beneath the ventilation layer and the tiles is one of the most important factors for the hygrothermal performance of pitched roofs. The air layer between tiles and sub-roof and the air exchange with the outdoor air influence the heat transfer and therefore affect the moisture level inside the roof construction. The paper aims to discuss these issues.

Design/methodology/approach

This paper provides the results of a research project performed at Fraunhofer-Institute for Building Physics, based on field test results. The investigations analyze the thermal behavior of different vented and ventilated roof constructions.

Findings

It was found that for a detailed model with roof cladding and ventilated air layer normally too many parameters are unknown. For that reason a simplified approach was set up, especially to consider the radiation exchange between the tiles and the underlay as well as the effects of the ventilation.

Originality/value

Now, effective surface transfer parameters can substitute both cladding and air layer in the simulation, while the approach still provides a high accordance with the measured values. The paper provides characteristic values for different roofing situations to simulate ventilated roofs by means of hygrothermal simulation in a simplified way.

Details

International Journal of Building Pathology and Adaptation, vol. 37 no. 4
Type: Research Article
ISSN: 2398-4708

Keywords

To view the access options for this content please click here
Article

Yuchai Sun, Xiaogang Chen, Zhonghao Cheng and Xunwei Feng

The purpose of this paper is to present the results of a study on heat transfer through a textile assembly consisting of fabric and air layers based on a theoretical model…

Abstract

Purpose

The purpose of this paper is to present the results of a study on heat transfer through a textile assembly consisting of fabric and air layers based on a theoretical model capable of dealing with conductive, convective and radioactive heat transfer.

Design/methodology/approach

Quantificational results were given out by the aid of finite element (FE) analysis software MSC MARC Mentat.

Findings

Significant findings through this paper include the change in heat flux against time and the transit temperature distribution at the cross‐section of the fabric assembly. The size of the air gaps has a significant influence on the heat transfer. The balance heat flux drops by 40 per cent when the air gap increases from 2 to 10 mm. The influence of the air gap tends to become smaller as the air gap is further increased. The number of fabric layers in the textile assembly has a noted influence, more so when the ambient temperature is lower. Comparisons between the theoretical and tested results show a good agreement.

Originality/value

This paper has established a new method for clothing comfort study by making use of a general purpose FE method software package.

Details

International Journal of Clothing Science and Technology, vol. 22 no. 2/3
Type: Research Article
ISSN: 0955-6222

Keywords

To view the access options for this content please click here
Article

Ming Fu, Wenguo Weng and Hongyong Yuan

– The purpose of this paper is to measure the thermal insulation of protective clothing with multilayer gaps in low-level heat exposures.

Abstract

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.

Details

International Journal of Clothing Science and Technology, vol. 26 no. 5
Type: Research Article
ISSN: 0955-6222

Keywords

To view the access options for this content please click here
Article

Long Thanh Cung, Nam Hoang Nguyen, Pierre Yves Joubert, Eric Vourch and Pascal Larzabal

The purpose of this paper is to propose an approach, which is easy to implement, for estimating the thickness of the air layer that may separate metallic parts in some…

Abstract

Purpose

The purpose of this paper is to propose an approach, which is easy to implement, for estimating the thickness of the air layer that may separate metallic parts in some aeronautical assemblies, by using the eddy current method.

Design/methodology/approach

Based on an experimental study of the coupling of a magnetic cup core coil sensor with a metallic layered structure (consisting of first metal layer/air layer/second metal layer), which is confirmed by finite element modelling simulations, an inversion technique relying on a polynomial forward model of the coupling is proposed to estimate the air layer thickness. The least squares and the nonnegative least squares algorithms are applied and analysed to obtain the estimation results.

Findings

The choice of an appropriate inversion technique to optimize the estimation results is dependent on the signal-to-noise ratio of measured data. The obtained estimation error is smaller than a few percent, for both simulated and experimental data. The proposed approach can be used to estimate both the air layer thickness and the second metal layer thickness simultaneously/separately.

Originality/value

This model-based approach is easy to implement and available to all types of eddy current sensors.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 38 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

To view the access options for this content please click here
Article

Yelin Ko, Sora Shin, Yong Seok Choi, Byung-Hee Hong, Sang-Yoon Park and Joo-Young Lee

The purpose of the study was to explore heat-accumulative and thermal-conductive characteristics of copper-graphene composite film (Cu-G film) while applying it to a…

Abstract

Purpose

The purpose of the study was to explore heat-accumulative and thermal-conductive characteristics of copper-graphene composite film (Cu-G film) while applying it to a human-skin analogue.

Design/methodology/approach

In the preliminary experiment, the authors evaluated the thermal conductive characteristics of the Cu-G film in three covered conditions (no film, copper film, and Cu-G film conditions). For the first factorial experiment, the heat-accumulative properties over heated pig skin were compared at air temperatures of 10, 25 and 35°C. For the second factorial experiment, 105 trials were conducted on pig skin by combining air temperatures, trapped air volumes, and numbers of film layers.

Findings

The results from the preliminary experiment showed that the Cu-G film distributed the surface heat to the outside of the Cu-G film, which resulted in even distribution of heat inside and outside the Cu-G film, whereas the copper film accumulated heat inside the copper film. The human-skin analogue of pig skin, however, showed the opposite tendency from that of the plastic. The pig-skin temperatures beneath the Cu-G film were higher than those beneath the copper film, and those differences were remarkable at the air temperature of 10°C. The accumulative heat was affected by the trapped air volume, fit to the skin, and number of Cu-G film layers.

Originality/value

In conclusion, the Cu-G film more effectively accumulated heat on the human-skin analogue than copper film, and those effects were more marked in cold environments than in mild or hot environments.

Details

International Journal of Clothing Science and Technology, vol. 32 no. 4
Type: Research Article
ISSN: 0955-6222

Keywords

To view the access options for this content please click here
Article

Slavko Vujević and Petar Sarajčev

This paper aims to describe a numerical procedure for approximating the potential distribution for a harmonic current point source, which is either buried in horizontally…

Abstract

Purpose

This paper aims to describe a numerical procedure for approximating the potential distribution for a harmonic current point source, which is either buried in horizontally stratified multilayer earth, or positioned in the air. The procedure is very efficient and general. The total number of layers and the source position in relation to the medium model layers are completely arbitrary.

Design/methodology/approach

The efficiency of the computation procedure is based on the successful application of the numerical approximation of two kernel functions of the integral expression for the potential distribution within an arbitrarily chosen layer of the medium model. Each kernel function of the observed layer is approximated using a linear combination of 15 real exponential functions. Using these approximations and the analytical integration based on the Weber integral, a simple expression for numerical approximation of potential distribution within boundaries of the observed medium layer is given. Potential retardation is taken into account approximately.

Findings

The numerical procedure developed for the approximation of potential distribution for a harmonic current point source, which is positioned arbitrarily in air or in horizontally stratified multilayer earth, is efficient, numerically stable and generally applicable.

Research limitations/implications

Numerical model developed for the harmonic current point source is the basis of a wider numerical models for computation of the harmonic and transient fields of earthing system, which consists of earthing grids buried in horizontally stratified multilayer earth and metallic structures in the air.

Originality/value

This is efficient and numerically stable frequency dependent harmonic current point source model. Potential retardation, which has been neglected at the first step of the approximation, is subsequently added to the potential expression in such a way that the Helmholtz differential equation has been approximately solved without introducing the Sommerfeld integrals.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 27 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

To view the access options for this content please click here
Article

Chrysoula Pandelidi, Tobias Maconachie, Stuart Bateman, Ingomar Kelbassa, Sebastian Piegert, Martin Leary and Milan Brandt

Fused deposition modelling (FDM) is increasingly being explored as a commercial fabrication method due to its ability to produce net or near-net shape parts directly from…

Abstract

Purpose

Fused deposition modelling (FDM) is increasingly being explored as a commercial fabrication method due to its ability to produce net or near-net shape parts directly from a computer-aided design model. Other benefits of technology compared to conventional manufacturing include lower cost for short runs, reduced product lead times and rapid product design. High-performance polymers such as polyetherimide, have the potential for FDM fabrication and their high-temperature capabilities provide the potential of expanding the applications of FDM parts in automotive and aerospace industries. However, their relatively high glass transition temperature (215 °C) causes challenges during manufacturing due to the requirement of high-temperature build chambers and controlled cooling rates. The purpose of this study is to investigate the mechanical properties of ULTEM 1010, an unfilled polyetherimide grade.

Design/methodology/approach

In this research, mechanical properties were evaluated through tensile and flexural tests. Analysis of variance was used to determine the significance of process parameters to the mechanical properties of the specimens, their main effects and interactions. The fractured surfaces were analysed by scanning electron microscopy and optical microscopy and porosity was assessed by X-ray microcomputed tomography.

Findings

A range of mean tensile and flexural strengths, 60–94 MPa and 62–151 MPa, respectively, were obtained highlighting the dependence of performance on process parameters and their interactions. The specimens were found to fracture in a brittle manner. The porosity of tensile samples was measured between 0.18% and 1.09% and that of flexural samples between 0.14% and 1.24% depending on the process parameters. The percentage porosity was found to not directly correlate with mechanical performance, rather the location of those pores in the sample.

Originality/value

This analysis quantifies the significance of the effect of each of the examined process parameters has on the mechanical performance of FDM-fabricated specimens. Further, it provides a better understanding of the effect process parameters and their interactions have on the mechanical properties and porosity of FDM-fabricated polyetherimide specimens. Additionally, the fracture surface of the tested specimens is qualitatively assessed.

Details

Rapid Prototyping Journal, vol. 27 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

To view the access options for this content please click here
Article

Gnanauthayan G., Rengasamy R.S. and Vijayakumar Kothari

This paper aims to deal with the thermal resistance of multilayer nonwovens. The effect of fibre denier, cross-sectional shape and positioning within the layers were…

Abstract

Purpose

This paper aims to deal with the thermal resistance of multilayer nonwovens. The effect of fibre denier, cross-sectional shape and positioning within the layers were analysed with respect to the thermal resistance. Moreover, effect of compression on thermal resistance of the multilayer nonwoven structure have also be studied.

Design/methodology/approach

The study involves multiple layering of thermal bonded nonwoven webs and the effect of fibre denier and positioning of different nonwovens from the hot plate. To avoid the increase in thermal resistance because of the air gaps between layers, the nonwovens were enclosed within an acrylic frame to compress them to a thickness of 12 mm. Compressional behaviour of the nonwovens were tested at a rate of 5 mm/min with peak compressive load of 50 N. Multilayer nonwoven assemblies were tested for thermal resistance with compressive pressure of 3.5 gf/cm2 and compared with that tested at zero pressure.

Findings

In the study, three-layered nonwoven structure, provided better thermal resistance than their single component counterparts. The structural characteristic of the multilayer nonwovens affected the conductive, convective and the radiative heat transfer. In a multi-layer nonwoven, the top most layer should have the finest fibre as possible. Second preference may be given to the middle and followed by bottom layers in terms of fibre fineness. However, fine solid fibres performed poorly in terms of compression and recovery resulting in poor thermal resistance under compressive load.

Originality/value

The experimental approach of controlling thickness while evaluating the thermal resistance will help in nullify the effect of air gaps between the layer interface, thus focussing on the effect of fibre denier and the positioning of nonwovens. This paper also discusses the unique properties of fine solid fibre and hollow fibres and their role in providing better thermal insulation for extreme cold weather applications.

Details

Research Journal of Textile and Apparel, vol. 22 no. 2
Type: Research Article
ISSN: 1560-6074

Keywords

To view the access options for this content please click here
Article

Meng Deng, Yunyi Wang and Peijing Li

The purpose of this paper is to provide the details of developments to research works in the distribution characteristics of the air gaps within firefighters’ clothing and…

Abstract

Purpose

The purpose of this paper is to provide the details of developments to research works in the distribution characteristics of the air gaps within firefighters’ clothing and research methods to evaluate the effect of air gaps on the thermal protective performance of firefighters’ clothing.

Design/methodology/approach

In this paper, the distribution of air gaps within firefighters’ clothing was first analyzed, and the air gaps characteristics were summarized as thickness, location, heterogeneity, orientation and dynamics. Then, the evaluation of the air gap on the thermal protective performance of fighters’ clothing was reviewed for both experimental and numerical studies.

Findings

The air gaps within clothing layers and between clothing and skin play an important role in determining the thermal protective performance of firefighters’ protective clothing. It is obvious that research works on the effects of actual air gaps entrapped in firefighters’ clothing on thermal protection are comparatively few in number, primarily focusing on static and uniform air gaps at the fabric level. Further studies should be conducted to define the characteristic of air gap, deepen the understand of mechanism of heat transfer and numerically simulate the 3D dynamic heat transfer in clothing to improve the evaluation of thermal protective performance provided by the firefighters’ clothing.

Practical implications

Air gaps within thermal protective clothing play a crucial role in the protective performance of clothing and provide an efficient way to provide fire-fighting occupational safety. To accurately characterize the distribution of air gaps in firefighters’ clothing under high heat exposure, the paper will provide guidelines for clothing engineers to design clothing for fighters and optimize the clothing performance.

Originality/value

This paper is offered as a concise reference for researchers’ further research in the area of the effect of air gaps within firefighters’ clothing under thermal exposure.

Details

International Journal of Clothing Science and Technology, vol. 30 no. 2
Type: Research Article
ISSN: 0955-6222

Keywords

1 – 10 of over 13000