Vapour—liquid equilibrium of nitrogen—oxygen mixtures and air at high pressure

The vapour liquid equilibrium surface of the binary mixture nitrogen—oxygen is correlated over an extended critical region with the Leung-Griffiths model as modified by Rainwater and Moldover. No single comprehensive experimental measurement of the coexistence surface is available. However, several different experiments along isopleths, isotherms and isobars collectively provide enough data to make possible the development of a reasonable correlation. The model is optimized to modern data and is shown to be consistent with pioneering measurements done before 1930, to within experimental and temperature-scale uncertainties. It is shown that air in the critical region can be accurately modelled as a nitrogen—oxygen binary mixture by including the small argon component with oxygen. Ancillary equations for the saturation properties of air as functions of temperature are also constructed.