Learning Forum

[DTUChemEng2020]

Dear CFD community,

I am modelling a two fluid one phase system in ANSYS CFX, where one of the approaches is a multiphase homogeneous model. The working fluids are glycerol and water. My question is, why do I see that there are separate fields (e.g. , velocity, pressure) for glycerol and water. To my understanding, when specifying a homogeneous mixture in CFX, then one set of equations are solved for 1 phase, since the multiphase model solves for n-phases. What does it mean then that there is a glycerol.velocity and a water.velocity?

 

Thanks in advance.

[DrAmine]

Hi,

First of all your glycerol is miscible with water: so actually there is no need to use multi-phase model at all.

For the particular rmultiphase question: homogeneous model means a single set of momentum equation + pressurized continuity equation + non-ballast /phase equations.

In post-processing you will see phase.Velocity for both phases: That is only post-processing. If you consider the out file you will see only one velocity field written

 

[DrAmine]

EDIT: Moving to Fluids

[DTUChemEng2020]

Thank you so much for your fast response. I know that there was no need to do a multiphase model, but the point was to test the difference between a multicomponent model where i specify the composition of the mixture to vary and mass fractions at boundaries, and the homogeneous model to investigate the best way to model a static mixer. My results for both instances are practically identical, which should be expected, since they are basically the same expect the one is mass fraction based, and the other requires the volume fraction.

 

 

[DrAmine]

Yes assuming very small molecular diffusion you will end up with almost identical result! I guess you used the drift flux model right? If yes that is rather a multiphase model based on mass fraction transport equation (no molecular diffusion)