Simulating Flow Boiling

  • Last Post 12 December 2018
zakmt293 posted this 27 November 2018

Hi I am simulating Flow Boiling in a 2-dimensional geometry. In which the fluid is flowing and I have to write the  UDF accordinglly.

As the cell temp is greater than T_SAT=162 then evaporation would occur. So for this pupose I have to add source terms as a vapor source. Kindly if someone can help me with this macros

THREAD_SUB_THREAD=(mix_th,1) what is the physical meaning of it if I write it in my UDF. 

THREAD_SUPER_THREAD(pri_th) What does this macro do physically 

Thank You 

Zeeshan Ahmad Khan

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rwoolhou posted this 27 November 2018

Unfortunately as staff we can't give too much detail in this scenario. There are boiling models already in Fluent which may be sufficient for your needs. 

The two macros should be in the manual, but very simply refer to one of the phase threads and the overall phase domain respectively (it's slightly more complex than that but I can't comment on a public forum). 

zakmt293 posted this 27 November 2018

Do you mean that one of them the first one refer to the secondary phase having id of 1 while the other one refer to the whole primary phase ???


Kremella posted this 27 November 2018


I'd strongly encourage you to read sections Phase-level thread pointer and Mixture thread pointer in the Fluent Customization manual to understand more about these macros. Here is a screenshot of one.

I hope this helps.

Best Regards,


zakmt293 posted this 28 November 2018

Thank You Dear Kremella for your help actually I am reading the manual but I am not getting a very clear understanding. I would be thankful if you can help me in how can I use them in solving my problem.

I want to access the primary phase which is liquid R134-a and the only fluid moving in the geometry in initially. As the temp of the any cell becomes greater than T_SAT it would be replaced by vapor ( the secondary phase). How can I use such macros in order to access this.


My main problem is that I am not understanding which of the above macros could be used to address the specific requirements. I am going through the  manual but I am not getting it. Any kind of tutorial or any kind of guidance would be appreciated

Thank You 

rwoolhou posted this 28 November 2018

We don't have many (if any: I'm not aware of any) publicly available UDF tutorials, and UDF support tends to be more limited than normal to even our commercial clients. Multiphase also brings an extra level of complexity due to the phase threads.

Does your University have software? 

zakmt293 posted this 12 December 2018

I am so sorry for late reply.

Yes we do have ansys 16 licensed version but how could that help me.

Thank you and again sorry for being late 

rwoolhou posted this 12 December 2018

No worries. The reason for asking about the University is that your supervisor may be able to contact the local support team for assistance: also to model boiling you may need more mesh than the Student version allows. 

I strongly recommend using R19.2 for this as multiphase modelling has been getting a lot of development work over the last few years: the next few releases will be better again.