**AIR**

The thermodynamic and transport properties of air are implemented assuming that air obeys the ideal gas law. Using ideal gas relations, it is only necessary to know how the specific heat varies with temperature in order to determine all thermodynamic properties. For temperatures between 100 K and 2000 K, the Air property routines use the ideal gas specific heat relation given in:

E.W. Lemmon, R.T. Jacobsen, S.G. Penoncello, and Daniel Friend

"*Thermodynamic Properties of AIr and Mixtures of Nitrogen, Argon, and Oxygen from 60 to 2000 K at Pressures to 2000 MPa*",

J.Phys.Chem. Ref. Data, Vol. 29, No. 3, 2000.

For temperatures between 2000 K and 3500 K, the thermodynamic properties are based on data from Keenan, Chao, Kaye, ** Gas Tables,** Wiley, 1983.

Transport property correlations are based on tabular data available from:

*Thermophysical Properties of Matter*

Vol. 3: Thermal Conductivity, Y.S. Touloukian, P.E. Liley, S.C. Saxena

Vol. 11: Viscosity, Y.S. Touloukian, S.C. Saxena, and P. Hestermans

IFI/Plenun, NY, 1970, ISBN 0-306067020-8

The range of validity of the viscosity correlation is between 80 K and 2000 K. The thermal conductivity correlation covers the range between 80 and 1500 K.

Note: Air does NOT use the JANAF table reference states for enthalpy and entropy and can not be used in combustion calculations unless the reference state values are shifted. If combustion calculations are needed, a mixture of O2 and N2 should be used in place of air.

Air and Natural gas are the only substancse in the EES database that do not follow the ideal gas name convention. All other substances are modeled as a real substance if the fluid name is spelled out, (e.g., Nitrogen) and as an ideal gas if the fluid name is chemical formula (e.g., N2). Air is modeled as an ideal gas. However, Air_ha provides real fluid properties for the air mixture.

Note that the reference value used for entropy may differ from that used to produce tables in thermodynamic textbooks. Since differences in entropy values are always used, the reference value cancels and it should not matter what its value is.