As of my knowledge from metallurgical thermodynamics a phase is a thermodynamically stable and homogeneous entity made up of different species of a given concentration.
e.g = 'Austenite' is a phase of steel with a given (Fe, C) concentration (%wt). So, we can call the Iron and carbon to be species.
But we may observe that 'Austenite' is nothing but Fe&C atoms arranged in a particular structure, which happens to be FCC (Face centered cubic). In that sense, a phase is nothing but a homogeneous aggregate of species at a different length scale(a larger length scale).
My questions related to the fluid system are.
- What's the difference between a species and a phase in a solution (in a fluid)?
- Given a mixture of water+salt+sugar, with the conditions that 'salt' is homogeneously mixed in the water, while 'sugar' is inhomogeneously mixed in water. May you please define the phase and species respectively for this system?
- And if what does the transport of species in a fluid phase mean?