Absorption and reflection of infrared radiation by polymers in fire‐like environments

Abstract

SUMMARY In large‐scale fires, the input of energy to burning materials occurs predominantly by radiative transfer. The in‐depth (rather than just surface) absorption of radiant energy by a polymer influences its ignition time and burning rate. The present investigation examines two methods for obtaining the absorption coefficient of polymers for infrared radiation from high‐temperature sources: a broadband method and a spectral method. Data on the total average broadband transmittance for 11 thermoplastics are presented (as are reflectance data), and the absorption coefficient is found to vary with thickness. Implications for modeling of mass loss experiments are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

A numerical study of thermal degradation of polymers: Surface and in-depth absorption

“…However, for the in-depth absorption, the temperature curves decline in the top region after the peak value. As described in the Ref [32], the value of / 1  allows an estimate of the characteristic penetration depth of radiant flux. For clear PMMA, 80% of the energy has already been absorbed at a depth of 0.534 mm where 1 1870m    , namely the mechanism of heat transfer within the penetration depth is controlled by in-depth absorption and thermal conduction are important for the other portion.…”

“…Some other researchers performed sensitivity analyses, emphasizing the sensitivity coefficients of relevant model outputs with respect to the inputs, to study the importance of absorption mode [29][30][31]. Jiang [28] and Linteris [32] measured the average absorption coefficient of several polymers that can be inputted into numerical models, and also they provided generalized techniques for other polymeric materials. All these in-depth absorption and surface absorption measurements, achieved by the absence and presence of black carbon powder on the surface, were conducted at room temperature by water cooled equipment to avoid the degradation of polymers and limit the heat effect from environment.…”

Parameterization and Validation of Pyrolysis Models for Polymeric Materials

“…It should be noted that the average absorption coefficients obtained from this type of measurement depend on the thickness of material sample [28]. However, as long as the measured values indicate that most of the radiation is absorbed within a relatively small (<0.5 mm) depth, the impact of ignoring this dependence on the overall heat transfer is expected to be negligible.…”

“…Fo¨rsth and Roos [27] and Linteris et al [28] performed calculation of average emissivities for a wide range of synthetic polymers using wavelength-resolved data from an integrating sphere equipped with infrared spectrometer and by assuming 1025 to 1081 K grey body source (emulating an external fire). Most of the emissivity values were found to be above 0.9.…”

“…This approach was previously utilized by Jiang et al [30] and Linteris et al [28]. In our most recent adaptation of this approach [5], 1.5 mm thick film samples were exposed to 35 kW m -2 produced by a cone calorimeter heater.…”