Learning Forum

[Ajayc1160]

I am trying to simulate condensation of mixture of water vapor(0.025 mass fraction) and air @ 300K,27C ,1m/s coming in contact with cooling coils at constant temp of 283K. To perform this in fluent i used following 2 different scenarios

Case 1:

1)Using Mixture Eulerian model with built in condensation model (Lee model)

One phase is mixture of air and water vapor

Another phase is only water liquid . Condensation is then defined using mass transfer mechanism and I defined a custom function for setting saturation temperature depending on vapor pressure with UDF

Case 2:

Use species model physics , euler mixture and species transport model. Use two different mixtures , one phase is mixture of air and water vapor, the other phase is species mixture consisting of only liquid. I define mass transfer using species mass transfer model and saturation pressure is modified as function of temperature .

In both of these scenarios, the simulation diverges after 2nd iteration. I m attaching error due to divergence from both of these case below

[Ajayc1160]

I am attaching the domain and b.c used for this simulation below

[Rob]

Does the model run single phase? Strip out all the complex parts and work up: this helps you check for errors but also focuses attention to the section/model setting that fails.

[Ajayc1160]

Hi Rob

The model runs well when i create air and vapor as two different phases instead of using them as mixture.

[Ajayc1160]

In addition to this, to answer your question previously, yes, the model runs good for only single phase like air . I removed the phase change and have only air passing through the channel. It works fine

[Ajayc1160]

In addition, I see that when i run the model with mixture of air and vapor without any phase change,then the model works fine too. So the divergence has to do something with phase change

[Rob]

OK, so what would cause a sudden failure with phase change? How humid is the air if you run the system single phase?

[Ajayc1160]

Not sure what is causing this divergence with phase change. May be there is very high rate of condensation

[Rob]

Possibly. If air & vapour are different phases it's a different problem and you won't have a saturation value. If you alter the temperature so you're above the dew point does it run?

[Ajayc1160]

Hi Rob. Im dicussing this problem on /forum/discussion/15997/providing-0-mass-fraction-in-vaccum-condition#latest. I have added my latest comments there

[Ajayc1160]