A reference quality equation of state for nitrogen

A new formulation describing the thermodynamic properties of nitrogen has b een developed. New data sets which have been used to improve the representa tion of the p-p-T surface of gaseous, liquid and supercritical nitrogen, in cluding the saturated states are now available. New measurements on the spe ed of sound from spherical resonators have been used to improve the accurac y of caloric properties in gaseous and supercritical nitrogen. State-of-the -art algorithms for the optimization of the mathematical structure of the e quation and special functional forms for an improved description of the cri tical region were used to represent even the most accurate data within thei r experimental uncertainty. The uncertainty in density of the new reference equation of slate ranges from +/- 0.01% between 270 and 350 K at pressures less than 12 MPa, within +/- 0.02% over all other temperatures less than 5 50 K and pressures less than 12 MPa, and up to a maximum of +/- 0.6% at the highest pressures. The equation is valid from the triple point to temperat ures of 1000 K and pressures up to 2200 MPa. The new formulation yields a r easonable extrapolation up to the limits of chemical stability of nitrogen as indicated by comparison to experimental shock tube data. Constraints reg arding the structure of the equation ensure reasonable extrapolated propert ies up to temperatures and pressures of 5000 K and 25 GPa. For typical cali bration applications, the new reference equation is supplemented by a simpl e but also highly accurate formulation, valid only for supercritical nitrog en between 270 and 350 K at pressures up to 30 MPa.