Thermal Barrier Properties of Flame Resistant Nonwovens
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Date
2005-08-10
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Abstract
Heat flux through nonwovens takes place by conduction through air and fibers, infrared radiation and also by convection. Radiation heat transfer is found to be the dominant mode of heat transfer at temperatures higher than 400-500K [18]. Convection heat transfer is negligible in nonwovens due to the small size of the pores and tortuous nature of air channels. Therefore, for optically thick nonwoven material, effective thermal conductivity is given by the sum of its conduction and radiation components. In this research two methods were identified to determine radiative thermal conductivity.
In the first method, effective (total) thermal conductivity of needlepunched samples made from Nomex fibers was determined by using a Guarded Hot Plate instrument, while the conduction component was calculated by employing equations developed by Stark and Fricke (15). The radiative thermal conductivity (radiation component of effective thermal conductivity) was then determined by subtracting the conduction component from the effective thermal conductivity.
In the second method radiation component of effective thermal conductivity was calculated using the extinction coefficient of samples. The extinction coefficient was determined by using direct transmission measurements made using a Fourier Transform InfraRed (FTIR) spectrometer.
Results showed that while radiation was the dominant mode of heat transfer at temperatures higher than 530 K, the conduction component of effective thermal conductivity did not change much in the range of densities tested. Empirical models were developed for predicting the temperature difference across thickness of the fabric and the radiative thermal conductivity with R-square values of 0.94 and 0.88 respectively. Fabric density, fabric thickness, fiber fineness, fiber length, mean pore size and applied temperature were found to have significant effect on the effective thermal conductivity and its radiation component of needlepunched nonwoven samples.
A high correlation between the results of Method 1 (Guarded Hot Plate) and Method 2 (FTIR) was not seen. However, the absorbance measurements made using the FTIR spectrometer were found to have significant effect on the radiative thermal conductivity.
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Nonwovens Heat Transfer Radiation
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Degree
MS
Discipline
Textile and Apparel, Technology and Management
