Radiation transfer in vibrationally nonequilibrium gases

A technique is set out for calculating infrared radiation in vibrational-rotational bands of nonequilibrium molecular gases along nonuniform paths. The technique is based on the model of the random superposition of Elsasser bands applied to narrow spectral ranges. For determining the matrix elements of lines, use is made of the harmonic oscillator and rigid rotator approximation. At a reasonable sacrifice in accuracy, this allows one to apply the technique over a wide temperature range. For linear triatomic molecules, combining into groups of lines with almost identical lower-level energies is suggested. This considerably diminishes the expenditure of machine time when describing radiation transfer. A careful account of the changes in the contour of lines along the line of sight, including those associated with flow velocity, makes it possible to use the technique for highly nonuniform paths and supersonic flows. Testing was conducted on calculations for diatomic molecules and 2.7 and 4.3 μm CO2 bands. The values of the constants needed are given. The comparison carried out allows one to recommend the technique for routine calculations in numerical simulation of a wide range of heat and mass transfer problems.