Spectrum, and absorption in humid air, of thermal radiation from hydrogen jet flames using simplified radiation chemistry

Thermal radiation emitted by a hydrogen flame is attenuated as it propagates through humid air due to absorption by water vapour contained in the air. This study analyses spectral transmission of energy emitted by the hydrogen flame as it passes through humid air, determining the normalised spectral irradiance, the apparent absorbance, and the percentage of total energy transmitted. The emission spectra of the hydrogen flame and the absorption spectra of humid air are obtained from the HITEMP2010 database, applying the Voigt function under specific conditions for each medium: the hydrogen flame is modelled at 2300 K with water vapour mole fraction of 22%, while the humid air is modelled at 300 K with relative humidities of 10%, 50% and 100%. The results indicate that humid air can absorb between 10% and 20% of the energy radiated by the hydrogen flame in the first metre of propagation, with total absorption between 20% and 40% over a 10-metre path, depending on relative humidity. Spectral analysis shows that attenuation of total radiation does not follow the exponential behaviour predicted by the Beer–Lambert law, attenuation being determined by spectral mismatch between emission bands of the hydrogen flame and absorption bands of the humid air.