Development of a fundamental equation of state for the liquid region of a pure fluid from speed of sound measurements. Application to water

Abstract

The high level of the experimental precision recently reached in the measurement of speed of sound in the liquid region of fluids, together with the high thermodynamic worth of speed of sound, are the decisive elements increasing the interest in methods which allow to extract complete thermodynamic information from speed of sound data. This work presents a heuristic approach for the reduction of speed of sound data in the liquid region of a pure fluid into a fundamental dedicated equation of state. Contrarily to the methods reported in the literature for the present purpose, the proposed technique provides an analytical formulation rather than local values of the thermodynamic properties. A reduction procedure combining linear optimization procedure and non-linear multiproperty fitting was set up. The prediction capability of the method is presented for water as the interest fluid, over an extended pressure and temperature range of the liquid region; the comparisons with the available experimental values of several thermodynamic properties and with the recent IAPWS-95 equation are also given. The high quality of the obtained results assures that the proposed procedure can be regarded as an effective and robust method to draw a very precise equation of state for the liquid region of a fluid primarily from speed of sound data.