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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 It may also happen that a Multiphase Fluid consists of one pure substance and and as such are not Fluid Mixturesis not a Fluid Mixture (example is liquid water and its vapour staying in equlibrium).
Fluid Mixture is a sum of Fluid Components, which are pure chemical substances.
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