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.

中文翻译：

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丙二醇的声速测量和基本状态方程

为丙二醇开发了一个基本的状态方程。它是根据具有独立变量温度和密度的亥姆霍兹能量写成的。由于其基本性质，它可用于根据亥姆霍兹能量及其相对于自变量的导数计算所有热力学状态属性。特别注意不仅要准确再现可用的实验数据，还要纠正外推法。因此，该方程可用于混合模型中。为了发展当前的状态方程，可用的文献数据补充了新的实验声速测量，这些测量是在 293.2 K 到 353.2 K 的温度范围内进行的，压力高达 20 MPa。