## Fluids

#### Mixture with species transport (no reactions)

• giovanni_ianziti
Subscriber

Hello to everyone,

I`m working on a multiphase model of an heat pipe. In the closed volume I have 0.13 of liquid water and 0.87 of mixture (vapour+air).I`ve create the mixture with species transport model, because I`ve mass transfer between water liquid and vapour.

How many phases I must to use? Two: one for liquid and one for mixture? Or is better three phases: water, vapour and air?

• Rob
Ansys Employee

You need one phase for the water and a second phase for the species mixture.

• Rob
Ansys Employee

Yes, if you set the gas phase using the species you have above, and then you can either set the mixture properties as constant or volume (or mass) weighted. For cp use a polynomial if that's what the paper recommends: I'd be slightly wary of this as it'll also depend on the composition, but that may be accounted for as temperature & vapour volume fraction will correlate.

• giovanni_ianziti
Subscriber

• giovanni_ianziti
Subscriber

But I can`t assign to the mixture a constant density, the other properties yes but not the density.

The phases for you are :

first phase:water

second phases: vapour,air and mixture

Because I need mixture in the phases if I want create species transport.

thank you

• DrAmine
Ansys Employee

For density either you use an EOS (Equation of State) or harmonic law or UDF. So your secondary phase is the "Mixture" with two "components": Air and Vapor.

• giovanni_ianziti
Subscriber

• giovanni_ianziti
Subscriber

Can you explain in details how to insert the missing properties in the mixture (density,molar mass and enthalpy) please?

thank you very much

• DrAmine
Ansys Employee

Molar mass will be just mile fraction time the molar mass of the component so it is done automatically. For others you can use mass-weighted mixing, ideal-mixing-law or just use constant at first.

• Rob
Ansys Employee

Ah, easy one when you know!

Change the mixture density to volume weighted and press Change/create. Then go to the species and add the density you want for each. The solver is fairly intelligent in only asking for data that's needed, but can be a little confusing if you don't know the hierarchy in which things are set.

Enthalpy is only available when you turn on the evaporation/condensation models or set up mass transfer.

• Ajayc1160
Subscriber

Hello team

I would like to simulate condensation of mixture of air and water vapor. I would like to enter specific volume fractions of air and water vapor at the inlet.

When i choose mixture model in ansys, i m unable to enter specific volume fraction values. When i choose species transport, I am unable to enter condensation phenomena . What am i doing wrong here?

• DrAmine
Ansys Employee