A new method to calculate the thermodynamical properties of liquids from accurate speed-of-sound measurements

In this work, a new method for the determination of the thermodynamical properties of fluids, based on experimental speed-of-sound measurements, is described. This method consists in the solution of recursive equations (REM, Recursive Equations Method) for the determination of the density ρ(p,T) and specific heat capacity at constant pressure c_p(p,T), using the initial values of density ρ(p₀,T) and isobaric specific heat capacity c_p(p₀,T) known at a reference pressure p₀, as a function of the temperature, if the speed-of-sound function, u(p,T), is known, at least over a certain temperature and pressure range. A complete uncertainty analysis has also been developed. As an example of the good performances of this analysis method, firstly density and isobaric specific heat capacity have been calculated for water and the results have been compared with those predicted by the International Association for the Properties of Water and Steam 95 Formulation (IAPWS-95), as delivered by Wagner and Pruss. One more application has been made starting from experimental speed-of-sound values in pure acetone. These results have been compared with those calculated by the most advanced numerical integration methods and with the prevision of the dedicated NIST equation of state (EoS) by Lemmon and Span.