Thermal Radiation of Potassium in MHD Gases

The inevitable presence of potassium in MHD gases contributes to an increase in radiation heat exchange. Owing to the extremely high temperature in the duct, the alkali emits a spectrum of rays whose intensity is due mainly to a resonance pair at 7665 and 7699 Å. In the first part of the paper the authors recall the laws of emission spectroscopy as applied to cases where self-absorption is significant. For alkali seeding ratios such as are used in MHD flows, they establish a theoretical relationship which links the energy radiated by the potassium to the temperature of the gas, its thickness, the mean concentration of free alkali atoms, and the width of the potassium resonance line at 7665 Å. Having found excellent agreement between experimentally determined values of energy radiated by potassium (measured on small laboratory flames 7.8 and 13 cm in thickness) and values calculated from the formula derived in the first part of the paper, they calculate the thermal losses which could be expected in an industrial-size duct with a thermal power of 2000 MW. They observe that radiative losses due to the alkali are comparable to those due to radiation from carbon dioxide gas and water vapour. The calculative results also show that radiative losses account for about 40% of all losses, which reach 1.65 MW/m2 at the entrance to the conversion duct. (author)