# Source term in volume fraction equation

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• Last Post 23 April 2019
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gunjanauti posted this 19 April 2019

I am trying to solve a multi-phase model with evaporation happening. I have already developed a theoretical model for the evaporation (different from Lee's Evaporation-Condensation model). How to hook the volume fraction equation source term in fluent?

Kremella posted this 19 April 2019

Hi,

The VoF equation is a continuity equation for volume fraction and contains mass transfer terms in the RHS. The source term you are developing through a UDF has to be a mass source term. To include the effect of these terms, you have to hook the term to the Phase Interaction dialog box.

Please have a look at the following sections in the Fluent Theory Guide (FTG) and Fluent User's Guide (FUG).

• Section 26.2.10 - Including Mass Transfer Effects (FUG).
• Section 18.3.4 Volume Fraction Equation (FTG).
• Section 18.7 Modeling Mass Transfer in Multiphase Flows (FTG).

Thanks.

Best,

Karthik

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gunjanauti posted this 20 April 2019

Thanks for the help though I used a different approach while solving the problem. I used a source terms for both my phases in cell zone conditions. It is working but is that the correct approach?

And one more thing I wanted to ask was that, I want to initialize a flow as an inverted annular film flow, while doing that I am able to initialize the volume fraction correctly but wasn't able to link the temperature and velocity profile. Even though I have used a DEFINE_INIT function, the GUI for the initialization shows the default values. So which values is the solution using?

kkanade posted this 22 April 2019

please check function hook. here you may need to hook your udf for initialization.

gunjanauti posted this 23 April 2019

I have hooked the function already and yet it initializes the flow with different values than the given function in UDF. Is there something to do with patching?

abenhadj posted this 23 April 2019

Define Init overrides any field initialization. If temperature is defined in an Init UDF than it would take precedence.

Best regards,

Amine

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