Theoretical prediction and experimental characterization of radiative properties and thermal conductivities of fibrous aramid fabrics

Abstract

Nonwoven aramid fabric is widely used as thermal barrier of fireproofing clothing due to its inherent flame retardancy and light weight. In fire or high temperature scenario, radiative heat transfer becomes the predominant heat transfer mode inside firefighters’ clothing. In this work, Fourier transform infrared spectroscopy (FTIR) was adopted to measure the spectral transmittance and spectral extinction coefficients of four aramid fabrics with different porosity in infrared wavelength range between 2.5 and 25 μm. It was found that the radiative properties of fibrous aramid fabric are strongly dependent on its bulk density or porosity. The spectral extinction coefficient decreases with increasing porosity or decreasing bulk density. The infrared optical properties combined with infrared imaging measurements demonstrate that aramid fabric may be used as infrared semi-transparent textile. A predicted model, combined the effects of conduction-radiation heat transfer, has been developed to calculate the effective thermal conductivity of aramid fiber materials. The model implemented the Rosseland diffusion approximation to evaluate radiative thermal conductivity, and the Parallel-Series structural model to evaluate tortuosity-weighted phonic thermal conductivity. The predicted results were also compared with experimental data obtained from TPS method. This work provides useful information for future studies of heat transfer mathematical modeling of firefighters’ clothing.

Effect of layering sequence and ambient temperature on thermal insulation of multilayer high bulk nonwoven under extreme cold temperatures

“…It is also reported that the convective heat transfer through the fabric is only possible when the porosity of the fabric is more than 0.992 and it is less than 1% of total heat transfer. [21][22][23][24] From Table 4, it is seen that the thermal conductivity of single-layer nonwoven in multi-layered assembly is a function of temperature and fibre denier. For every single nonwoven layer in multi-layered assembly, the thermal conductivity decreases with a decrease in ambient temperature.…”

“…Heat transfer by convection is negligible (less than 1% of total heat transfer for porosity higher than 0.992) through the fibrous structure. [21][22][23][24] Heat transfer through the high bulk nonwoven fabric is considered a coupled conduction-radiation problem. [25][26][27] Mansoor et al 28 studied the effect of moisture percentage on the thermal insulation provided by the plain socks numerically and validated with experimental results.…”

Numerical simulation for the determination of the radiative properties of spherical packed bed porous media: A COMSOL Multiphysics Study

“…A number of researchers have addressed analytical solutions derived from extensive measurements and validations. 12,[25][26][27] With the significant progress in computational tools over the last decades, numerical methods have been developed for the prediction of the radiative properties of porous media. Many numerical simulations have been performed for spherical packed bed porous media by using different methods, alone or combined, 28 such as Monte Carlo ray-tracing (MCRT), 29,30 the radiative distribution function identification (RDFI), 31 discrete ordinate, 32 two-flux methods, 24 Finite Volume Method (FVM), 33,34 Finite Element Method (FEM), 35 the Mie theory and the discrete dipole approximation (DDA) 36 etc.…”