The properties appearing in the transport equations are determined by the presence of the component phases in each control volume. In a two-phase system, for example, if the phases are represented by the subscripts 1 and 2, and if the volume fraction of the second of these is being tracked, the density in each cell is given by

(14–13)

In general, for an -phase system, the volume-fraction-averaged density takes on the following form:

(14–14)

All other properties (for example, viscosity) are computed in this manner.