Non-classical gas dynamics of vapour mixtures

The non-classical gas dynamics of binary mixtures of organic fluids in the vapour phase is investigated for the first time. A predictive thermodynamic model is used to compute the relevant mixture properties, including its critical point coordinates and the local value of the fundamental derivative of gas dynamics Gamma. The considered model is the improved Peng-Robinson Stryjek-Vera cubic equation of state, complemented by the Wong-Sandler mixing rules. A finite thermodynamic region is found where the nonlinearity parameter Gamma is negative and therefore non-classical gas dynamics phenomena are admissible. A non-monotone dependence of Gamma on the mixture composition is observed in the case of binary mixtures of siloxane and perfluorocarbon fluids, with the minimum value of Gamma in the mixture being always larger than that of its more complex component. The observed dependence indicates that non-ideal mixing has a strong influence on the gas dynamics behaviour, either classical or non-classical, of the mixture. Numerical experiments of the supersonic expansion of a mixture flow around a sharp corner show the transition from the classical configuration, exhibiting an isentropic rarefaction fan centred at the expansion corner, to non-classical ones, including mixed expansion waves and rarefaction shock waves, if the mixture composition is changed.