Learning Forum

[giovanni_ianziti]

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]

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

 

[Rob]

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]

 

[giovanni_ianziti]

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]

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]

 

 

[giovanni_ianziti]

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]

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]

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]

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]

Please open a new thread for your question.