Sound velocity and isentropic exponents of real air on its compressibility chart
(EN)
Kouremenos, DA
(EN)
Antonopoulos, KA
(EN)
In previous publications, three real-gas isentropic exponents k(pv), k(Tv), and k(pT) have been introduced, which, when used instead of the classical exponent k = C(p)/C(v) in the ideal-gas isentropic-change equations, may be applied with great accuracy to real gases. The first of the exponents may also be employed for calculating the real-gas sound velocity as alpha = (k(pv)pv)1/2. The purpose of this study is to present the generalized compressibility chart (of the Nelson-Obert type) of real air and place on this chart the values of the real-air isentropic exponents and sound velocity based on its virial equation of state. The usefulness of such diagrams lies in the fact that they provide in a compact and concise form information about the thermodynamic behavior and the isentropic flow of real air, and they allow straightforward comparisons between air and other real gases. Using the Redlich-Kwong-Soave correlation with acentric factor omega = 0.035, similar diagrams for the air are presented and compared successfully with the corresponding exact ones.
(EN)
