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[98546948]

Hello everyone,

I get into trouble, when using VOF method for a heat pipe simulation. I hope someone can help me.  Here is my setup in Fluent.

Firstly, the VOF method is implemented. And Body Force Formulation is checked. The primary phase is vapor, and the secondary phase is liquid.

In addition, the working fluid is hydrogen.  the physical property parameters of fluids are functions of temperature. The surface tension coefficient is constant. 

The interaction between phases is simulation by UDFs that are compiled according to Lee Model. And the mass sources are added to vapor and liquid, respectively, and the energy is added to mixture in cell zone condition. 

PISO algorithm scheme is applied in Solution Method. And the Discretization of Volume Fraction is Geo-Reconstruct.

Lastly, a saturation state of fluid is implemented as an initial condition, and the liquid volume fraction is 0.5. The time step is 1e-4. 

Then the calculation starts. But the results were not satisfactory.

when the density of vapor is the function of temperature,  the mass conservation can't  maintain and  the pressure inside the container fluctuates. when the vapor is assumed to ideal gas, the mass is conserved, but the pressure keeps increasing. What is the difference between the two Settings? 

So I need some help that whether there is something wrong in my case. And how to understand the processes of pressure calculation?

Thanks a lot. 

[Amine Ben Hadj Ali]

Why are you using UDF's for mass transfer instead of the implemented Lee Model?

Ideal EOS: Density depends on pressure and Temperature whereas your density does only have one degree of freedom. 

 

[98546948]

Thanks your reply, Amine. The Lee Model in Fluent sometimes can't be converged, when changing the frequency of evaporation and condensation. So I choose to use UDFs. Which range of evaporation frequency and condensation frequency do you think are reasonable? And it's a shame that I can't understand your explanation of density, and how to set up the density to be a function of temperature and pressure? 

Best regards

 

[Amine Ben Hadj Ali]

from values near zero to values near 1000.

to have density in function of both pressure and temperature: either ideal gas or real gas in Fluent. If you have some high end EOS law you can implement it via UDF.

[amaligaadi2018]

please can you share UDFs of the interaction between phases

[Rob]

There are some examples in the UDF manual, but otherwise we don't share code as it usually contains proprietary information. 

[98546948]

Thanks sir. There are some new questions.  In multiphase flow, how to call the real gas model in Fluent? The Help Document has some description like this:

And I compiled density in function of both pressure and temperature by MATLAB, but the solver just calculated a few time steps then diverged.

So, It's confused that how to set up the density of gas when using VOF model. Please make some recommendations.

Thanks you

Best regards