Novel high pressure critical phase transitions in multicomponent fluid mixtures

Abstract

New results are presented for the critical equilibria of ternary mixtures. The critical conditions of a ternary mixture have been solved (using the Guggenheim equation) for a wide range of pressures, temperatures and volumes, and over the entire range of compositions. The analysis, which has been applied to a wide variety of ternary mixtures, indicates that novel critical transitions are possible which have no direct parallel in binary mixtures. In particular, a critical transition is commonly observed between two different types of two-phase equilibria. This is in contrast to normal critical equilibria in binary mixtures or pure fluids which involve the transformation of two coexisting phases to form a single homogeneous phase. This result has implications for the interpretation of tricritical and other multiphase transitions which may instead be manifestations of a broader type of critical transition.