A classification of phase diagrams of ternary fluid systems

Phase diagrams and critical states of ternary fluids mixtures are calculated from the van der Waals equation of state with standard 1-fluid mixing rules. Berthelot-Lorentz combining rules are assumed for the binary interaction parameters. The topological classes of the resulting ternary phase diagrams are determined and their relationship to the classes of the binary subsystems discussed. It is shown that the phenomena of "miscibility windows'' and "miscibility islands'' are connected with a special ternary phase diagram class and can be reproduced even with the van der Waals equation of state.