Abstract: The instant invention relates to a method and apparatus to determine the thermodynamic properties of a gas medium without making a determination of gas composition. In the instant invention, the speed of sound of a gas medium in a vessel is determined at various temperatures and pressures based upon an isobaric process with estimated initial values of density, compressibility and numerical deriviative (dZ/dT) for the same gas medium. According to the preferred embodiment, this information may be measured at constant pressure or constant temperature. Once the physical information is determined, a routine is executed by which initial estimated parameters such as the compressibility and heat capacity of the gas medium will converge to accurate values. From these parameters, the thermophysical properties of the gas medium may be determined.

Abstract: The instant invention relates to a method and apparatus to determine the thermodynamic properties of a gas medium without making a determination of gas composition. In the instant invention, the pressure and speed of sound of a gas medium in a vessel are determined at multiple temperature points. According to the preferred embodiment, this information may be on a single isochore. Once the physical information is determined, an interpolation routine is executed by which initial estimated parameters such as the density and the compressibility of the gas medium will converge to accurate values. From these parameters, the thermophysical properties of the gas medium may be determined.