Fluid containing more than one phases at certain pressure and temperature conditions.
Each phase of the Multiphase Fluid is represented either by a pure substance or by a Fluid Mixture (see Multiphase Fluid vs Fluid Mixture).
This means that some Multiphase Fluids may consist of one pure substance and as such are not Fluid Mixtures.
The most popular multi-phase fluid are:
It is important to remember that multi-phase fluid may collapse to a single-phase state at certain pressure and temperature conditions.
For example, a 2-phase oil + gas fluid may degrade to single-phase state when pressure goes up above bubble point.
See also
Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase