Phase-transition radiation in vapor condensation process

Energy release by radiative relaxation during water vapor condensation is considered to be responsible for phase-transition radiation in the water vapor condensation process. A two-level transition model is proposed to explain the radiative transfer mechanism for condensation radiation of water vapor. The absorption coefficient due to condensation radiation and the associated optical properties are defined in the radiative transfer equation. The spectral profile of the source function of vapor condensation radiation is examined and agreement with the experimental characteristic wavelength of condensation radiation is found.