Speed-of-Sound Measurements and a Fundamental Equation of State for Propylene Glycol

Abstract

A fundamental equation of state was developed for propylene glycol. It is written in terms of the Helmholtz energy with the independent variables temperature and density. Due to its fundamental nature, it can be used to calculate all thermodynamic state properties from the Helmholtz energy and its derivatives with respect to the independent variables. Special attention was paid not only to accurately reproduce the available experimental data but also to correct extrapolation. Therefore, this equation can be used for application in mixture models. For the development of the present equation of state, the available literature data were supplemented with new experimental speed-of-sound measurements, which were conducted in the temperature range from 293.2 K to 353.2 K with pressures up to 20 MPa. High accuracy was achieved by applying the well-established double-path-length pulse-echo technique and a careful sample preparation.