Anomalous properties of dew-bubble curves in the vicinity of liquid–vapor critical points

• Equations of a mixture dew-bubble curve (DBC) near critical point are obtained.
• The Pρρ and Tρρ second derivatives along the DBC have cusps at the critical point.
• A method to estimate the mixture critical parameters from the DBC data is proposed.
• The method was tested for several multicomponent mixtures.

The explicit equation of dew-bubble curves in the vicinity of vapor–liquid critical points in mixtures has been derived within the scope of scaling theory and principle of isomorphism. It is shown that along these curves the pressure and the temperature depend non-analytically on the mixture density. As a consequence, the second derivatives (d2T/dρ2)DBC and (d2P/dρ2)DBC (taken along the dew-bubble curves) reveal cusp-like anomalies at the critical point. This specific feature enables one an easy estimation of the critical parameters of multicomponent mixtures directly from fitting a polynomial to dew-bubble-curve experimental data. To justify the proposed approach, the experimental data on dew-bubble curves for several binary and multicomponent mixtures have been analyzed and the positions of their critical points have been determined.