Sonic Properties in Non-Ideal Flows

The sonic properties of mono-component single-phase non-ideal flows are studied assuming steady, one-dimensional, inviscid, shock-free adiabatic flow. Under these hypotheses, the total enthalpy ht and entropy s are uniform in the flow, and the sonic properties density ρ∗, speed of sound c∗, momentum density ρ∗c∗, and momentum flux density ρ∗c∗2 are readily computed from the total thermodynamic state specified by the total pressure and temperature (Pt,Tt). Application-relevant fluids and operating conditions are considered and isentropic expansions from reservoir to sonic conditions are investigated using both state-of-the-art thermodynamic models and the ideal-gas model. The evolution of selected thermodynamic properties along isentropic expansions is monitored and maps reporting the sonic properties in the Pt-Tt thermodynamic plane are constructed to illustrate the mechanism of dependence of the sonic properties on the total thermodynamic states. Several different non-ideal thermodynamic effects are identified and commented, which determine remarkable qualitative and quantitative differences between ideal and non-ideal flows.