Speed of Sound in Mixtures of Liquids: Noble Gases and Water–Alcohol Mixtures

The possibilities of predicting the behavior of the speed of sound in water–alcohol mixtures in dependence of component concentration and under high pressure have been analyzed. A comparative analysis of the thermodynamic properties of water and methanol at high pressures, obtained experimentally and by molecular dynamics simulation for different computer models of water and methanol, was performed, which showed inadequate description of experimental data. It is demonstrated that the existing theoretical methods do not make it possible to study the speed of sound in water–alcohol mixtures at a high pressure, whereas the experimental methods are extremely laborious. Arguments are presented in favor of the fact that the qualitative behavior of the speed of sound in a water–alcohol mixture at high pressures should be similar to the behavior of a mixture of noble gases. The behavior of the speed of sound in an argon–helium mixture in dependence of the component concentration at a high pressure was investigated by the molecular dynamics method. This dependence was found to contain a minimum, which is in good agreement with the experimental data obtained at the same thermodynamic parameters and component concentrations. We present a qualitative explanation of the behavior of argon–helium mixture, based on the Frenkel line concept. Proceeding from this, we suggest that the speed of sound in a water–alcohol mixture under high pressure conditions should also demonstrate a minimum in the dependence on the component concentration.