Look at this doc it may be helpful for your topic. Good luck.

HIi Sachin,

We never use 2 mass transfer in evaporation-condensation model, instead we use only one mass transfer as the model itself takes care of both. Say u defined only evaporation and it will take condensation as negative mass transfer. Have a look at Lee model for further detail.

Now the crux of the model is the coefficients which u need to tune between 0.01 to 1000 as per the experimental observations.

For further queries and UDF, drop me a mail on 

[email protected]

Yes,

When you use VOF model:

Click Phases> interaction> Mass >

(From Phase)                 (To Phase)                          (Mechanism)

liquid                                 vapor                                evaporation-condesation

There is this routine in FLUENT

Choose the coefficients

Good luck

@Sachin Shinde try this code, may be helpful to you. 

Hello, Suppose I choose the VOF model and the inbuilt evaporation-condensation model in FLUENT. The theory guide says that FLUENT automatically adds source terms to momentum (not for VOF), energy and species equation. My question is, do I need a mass source term for each phase [cell zone conditions > phase > source terms >mass]? And, if i do that, am i adding source terms to continuity equation for each phase? Thank you  

@Mohamed.S.Yousef I have seen the UDF code provided by you. I have few queries regarding this. I request you to kindly clarify these: 1. Once the UDF is interpreted in Fluent, are udf terms representing mass of vapor and liquid and energy are to be added as Source terms under cell Zone conditons? OR as under mass tab of phase-interaction? 2. Another important thing I want to know is that how to find the mass of liquid evaporated and mass of vapor condensed and respective heat transfer? I mean where in Fluent I can get these values after the simulation. Thanks in advance!

Vidyadhar .K Energy source at every liquid domain, under "Zone Conditions", Mass transfer under Phase interaction--> create 2 mass mechanism and apply each one on one slot.

Vidyadhar .K , Christos Christou For Mass transfer under Phase interaction, did you mean create two mass transfers like,

If so, what specific term from the UDF should I use for the above respectively.

The UDF has terms namely

Hello Soumitra Vadnerkar

If you have used DEFINE_MASS_TRANSFER macro in your UDF, then the name of that macro would become visible under Phase Interactions.

If you have several such mass transfer macros which model mass transfer from liquid to vapor or vapor to liquid, then you can select them as you desire.

I do not know what the names vap_src and liq_src represent in your UDF? If they are DEFINE_MASS_TRANSFER macros, then you can.

Thanks & Regards,

Vidyadhar

Thank You Vidyadhar .K

I was referring to the UDF provided by @Mohamed S. Yousef above in the discussion.

There you can see the names vap_src, liq_src.

I just don't get how to use this UDF.

I am simulating a condensation problem between liquid water and vapor.

I tried with Lee's evapo_conden model and want to use and see the other UDF models as well.

I will try with DEFINE_MASS_TRANSFER macro UDF later as well.

Hello Soumitra Vadnerkar

I would suggest try the UDF provided by Mohamed S Yousef and see if it gives the results you need; either using that UDF directly or by slightly modifying it.

In that UDF, the macros are of DEFINE_SOURCE which are to be hooked on cell zones.

Thanks & Regards,

Vidyadhar

I completed a thesis on ANSYS FLUENT 18 on condensation inside a wickless thermosyphon. The (built-in) Lee model is enough to do the job.

*REMEMBER: Water should be the primary phase! vapor secondary.

I compared completely new UDFs against Lee, also switching between water vapor for primary phases (because calculations are performed in more detail for the secondary phase in VOF, so for condensation you want water to be simulated in more detail, i.e 2ndary = water-liquid). Even so, Lee was proven way better, even when a new UDF completely mimicked the Lee model but structured to fit water as 2ndary!

+However, based on the judgement of Fadhl et al. + Alammar et al. you could add a water density(ρ) and surface tension(σ) UDFs (which are really simple Temp-based equations). For more accurate results.

++For fast results you could do Implicit simulation. The VOF contours will be a mess but it will finish way faster than Explicit. Temp results will be adequate.

Vidyadhar .K So do you mean all the terms defined under DEFINE_SOURCE macro- liq_src, vap_src and enrg_src should be rather used under Cell zone conditions respective source terms?

if so, in that case, do I need to define Mass Transfer Mechanism under Phase Interactions?

Hello Soumitra Vadnerkar

1) If you hook DEFINE_SOURCE under cellZone

Then, DEFINE_MASS_TRANSFER -- may not be needed

2) Also, I suggest you to refer the Fluent UDF manual to understand about the macros and their purpose.

Note: please verify yourself whether you need to write an UDF for your problem or if the in-built model would suffice.

Regards,

vidyadhar

Yes, I would first figure out if the in built model is suffice or not.

thanks

Vidyadhar .K and Soumitra Vadnerkar : Have you guys been able to run the UDF that was provided by Mohamed S. Yousef above? Every time I set up the problem with the appropriate boundary conditions (simulating a thermosyphon), and try to initialize the problem, the Fluent setup closes without any error output.

Amey Shigrekar I stopped trying the UDF approach. Many said the Evapo-Conden model is good enough. And I think I agree with the model.

My case deals with condensation only.

The right coefficient though is tricky to find, I am still trying.

Amey Shigrekar Also, I had the same issue, during intialization , Fluent crashes.

Hello Amey Shigrekar

1. could you try running your Fluent case without loading UDF. See if it crashes.

2. If not, please check: hooking the UDFs and debugging the UDF line by line.