Speed of Sound Measurements and a Fundamental Equation of State for Hydrogen Chloride

A fundamental equation of state in terms of the Helmholtz energy is presented for hydrogen chloride. Any thermodynamic property can be calculated by combinations of its derivatives with respect to the independent variables temperature and density. The present equation of state is applicable in the entire fluid region. Its accuracy is assessed by comparison with the available experimental literature data from the triple point temperature to 480 K and a maximum pressure of 40 MPa. A reasonable extrapolation behavior beyond these temperature and pressure limits is ensured to allow for an application to mixture models. For the development of the present equation of state, speed of sound measurements are carried out in the liquid and dense vapor phases by means of the pulse-echo technique. Because no speed of sound measurements for this fluid are reported in the literature, the present experimental data set is crucial for the accurate modeling of caloric properties of hydrogen chloride.