ABSTRACT
Energy transfer through hot gases in furnaces, internal combustion engines, various combustion chambers at high pressures and temperatures, rocket propulsion, and spacecraft atmospheric reentry, among others, is a very important mechanism for radiative energy transfer. Predicting the radiative properties of these radiatively participating gases, including water vapor, carbon dioxide, carbon monoxide, methane, and others constitutes a challenge in calculating energy transfer. Although some of these applications are relatively recent, the study of radiation in gases has been of continuing interest for over 100 years. An early consideration was absorption and scattering of radiation in the earth’s atmosphere, as this interfered with observations of light from the sun and more distant stars. The solar spectrum received on the earth was originally recorded by Samuel Langley (1883); a schematic of this spectrum is shown in Figure 9.1. The uppermost solid curve in this gure is the incident solar spectrum outside the earth’s atmosphere; the blackbody emission spectrum at 6000 K is shown for comparison. The lowest solid curve, that has several sharp dips, indicating the spectrum received at ground level after the solar radiation has passed through the atmosphere along a path normal to the earth. The shaded regions show where radiation has been absorbed by various atmospheric constituents, mainly water vapor and carbon dioxide. Absorption occurs in specic wavelength regions, illustrating that gas radiation properties vary considerably with wavelength. Extensive discussions of absorption in the atmosphere are in Goody and Yung (1989) and earlier by Kondratyev (1969). Radiation by different gases is also of interest to astrophysicists studying stellar structure. The spectrum observed during the emission or absorption of radiation by a gas is characteristic of the specic gas, so it can be used as a diagnostic tool to determine the gas species, temperature, and concentration. Models of stellar atmospheres and the energy transfer processes within them have been constructed and compared with observed stellar behavior.
