K3 Gas Radiation: Radiation from Gas Mixtures


Gases emit thermal radiation, just as liquids and solids do, when they are at a temperature T > 0 K. Radiation from gases is typically much less intense, as the volumetric density of the source of radiation, the molecules, is low. According to Kirchhoff’s law, see Chap. K1 , gases that emit radiation also absorb radiation. Unfortunately, the intensity and wavelength of emittance and absorbance are dependent on the structure of the gas molecules and are quite complicated. Dry air, elementary gases – e.g., O2, N2, H2, – and the noble gases are practically diathermanous, i.e., transparent to thermal radiation. Other gases and vapors – e.g., H2O, CO2, CO, O3, SO2, HCl, NH3, and CH4 are selective radiators, i.e., they emit and absorb within narrow wavelength bands. Hydrocarbons also display characteristic emissivity and absorption to an extent that increases with the number of atoms in their molecules. In general, the spectral absorption and emission is a fingerprint of molecular structures which is used extensively for chemical spectroscopic analysis.

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K3 Gas Radiation: Radiation from Gas Mixtures
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VDI Heat Atlas
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Part of
  • Dieter Vortmeyer (1_66)
  • Stephan Kabelac Send Email (2_66)
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  • 1_66 Munich, Germany
  • 2_66 Helmut-Schmidt-Universität, Universität der Bundeswehr Hamburg, Hamburg, Germany
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