USE OF THE VELOCITY OF SOUND IN PREDICTING THE PVT RELATIONS

Thermodynamic properties of fluids are generally calculated from the P VT relations through equations of state. The majority of existing equa tions of state require the critical properties or intermolecular poten tial energy parameters as their input data. In many cases, such proper ties are neither available nor they can be accurately estimated. One a ccessible and accurately measurable property of substances is the velo city of sound. In this report a method is introduced through which one can predict the PVT behavior of fluids using the velocity of sound da ta. A general mathematical relationship, c2 = c2 hs + - V2/M integral- infinity/T (partial derivative 2T/partial derivative V2) s (partial de rivative s/partial derivative T) V dT expressing the velocity of sound , c, in terms of the hard-core velocity of sound, C(hs), and thermodyn amic properties is derived. One may use this equation to extract PVT d ata from cVT data, or vice versa. As an example the virial coefficient s, the Lennard-Jones intermolecular potential parameters, and the cons tants of the van der Waals equation of state for a number of pure flui ds are calculated using the velocity of sound data. Utility of this me thod is particularly attractive for such compounds as heavy hydrocarbo ns, unstable fluids, and newly designed molecules for which intermolec ular parameters and critical properties are not available.