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Radiation Emissions from Water Vapor Bands

The hydrogen-air flame emit infrared (heat) radiation mainly due to water vapour bands in the 1-6 μm wavelength region. The contribution of atoms and radicals to heat radiation in hydrogen flame is negligible. However, as mentioned earlier, OH radical effects the maximum temperature of the flame.

Figure 1 shows the comparison of the predicted and measured radial temperature distribution of H2-air flame for different degrees of dilution by natural gas, the dilution ranging between 0 and 100 %. The measured values shown in Fig. 1(a) have been derived from OH fluorescence signals, and the predicted values shown in Fig. 1(b) have been computed using detailed chemical kinetics.

It can be seen from the figure that the peak temperature of the 100 % hydrogen-air flame is 2320 K and that of the 100 % natural gas-air flame is 1600 K. The lower peak temperature of the natural gas flame is attributed to the higher heat losses both in the form of banded non-luminous radiation from CO2 and continuous luminous radiation from solid soot particulates, which are absent in the H2-air flame. Both flames have heat losses from banded non-luminous radiation from H2O. The computed stoichiometric temperature contours using the detailed chemical kinetics show a similar trend for the different mixture conditions. Compared to experimental results, predicted temperatures are higher and steeper in shape for all mixture conditions.

Liu et al. (LiuLH:2004) have considered 6.3 μm, 2.7 μm, 1.87 μm, and 1.38 μm infrared bands of water vapor to calculate frequency distributions of radiative source terms. Due to different band intensity parameters and temperature for each band, the symmetrization of frequency distributions in each band is different. The symmetrization of frequency distributions for the radiative source term at 6.3 μm and 2.7 μm bands is better than at 1.87 μm and 1.38 μm bands.

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Page last modified on February 18, 2009, at 02:27 PM