In chemical engineering, mixtures containing multiple components are of vital importance. However, the state of mixtures does not only depend on temperature and total pressure, but also on the composition. In particular, information about the vapor-liquid equilibrium (VLE) is needed, e.g. for processes like distillation. In the VLE the vapor and liquid phase coexist at the same temperature and total pressure, but usually with different - though not independent - compositions.
For a mixture with three components the VLE data can be illustrated using a three-dimensional graph. The pure components are represented by the vertices of an equilateral triangle. The edges correspond to binary mixtures. Any point in the interior of the triangle represents the ternary mixture with a certain composition. The mole fractions of each component correspond to the positions of the orthogonal projections of a point onto the angle bisectors. The third dimension is used for the temperature. (Note that the total pressure is the same for all data points.) Now bubble point and dew point data become curved surfaces which are colored blue and red, respectively. Further, a plane is utilized to visualize the distribution of liquid, vapor and VLE for a certain temperature.