Assessment of Three Databases for the NASA Seven-Coefficient Polynomial Fits for Calculating Thermodynamic Properties of Individual Species

Abstract

This work considers the seven-coefficient polynomials proposed by the National Aeronautics and Space Administration (NASA) to facilitate obtaining a normalized value for three thermodynamic standard-state specific properties of ideal gases or condenser matters over an interval of temperature. These properties are the heat capacity at constant pressure, the absolute enthalpy (sensible enthalpy plus heat contents due to chemical or physical changes), and the entropy. In the open literature, one can find several databases for the polynomial coefficients with variation in the number of species included or the range of temperature covered, and this raises a question of whether the choice of a database to use has an important impact on these evaluated thermodynamic properties. Addressing this point, we compare and assess three databases for the NASA 7-coefficient polynomials, over a selected range of temperature from 300 K to 3500 K, and for selected six common gaseous species encountered in combustion or industrial processes, which are molecular oxygen (O2), molecular nitrogen (N2), molecular hydrogen (H2), methane (CH4), carbon dioxide (CO2), and water vapor (H2O). Our comparisons suggest that despite the difference in the values of coefficients, there is no significant difference in their predictions. However, the latest (7th edition) database of Prof. Alexander Burcat hosted at Eötvös Loránd University (ELTE) in Budapest, Hungary showed superior features when contrasted to other two databases (one accompanying the simulation package OpenFOAM 6, and another provided by the natural-gas reaction mechanism GRI-MECH 3.0).