UDF is not being executed?

JeroenJeroen Member

I am trying to model a particle surface reaction, and i have activated this via the species model (see below). For this reaction, I am using the DEFINE_PR_RATE type UDF which I have hooked. Also, I have disabled the coupled heat-mass solution in the discrete phase model dialog box, as suggested in the manual. However, when doing a discrete phase iteration the UDF is not executed somehow. What is causing this?


  • RobRob UKForum Coordinator

    Turn on the Interaction with Continuous Phase otherwise there can be no particle reactions.

  • JeroenJeroen Member

    I have tried activating the continuous phase interaction, however the UDF is still not being executed.

  • RobRob UKForum Coordinator

    I don't know, have you met the requirements for the particle to react (eg activation energy), have you set up the reaction scheme etc? What is happening in the model?

  • JeroenJeroen Member

    I have set the activation energy to 0, such that the reaction should take place immediately. Reaction mechanism has been set up using the following reaction scheme:

    The solid species here are fe3o4 and fe, and h2 and h2o are gasses. The reaction should occur at the particle surface however using the current variables for the arrhenius rate and particle surface reaction is insufficient to describe the process. Hence, I wrote the PR_RATE UDF to describe the reaction rate. This UDF should thus overwrite the reaction rate properties specified in the window above.

    Also, I am currently using a multicomponent discrete phase particle where the solid components have been re-specified. However, in reality these components are equal to the solid species. Therefore I have used the same molecular formula. I wonder though how Fluent should know that it should use these components for the particle surface reaction. Should I use a different particle type or specify my particle components in a different way?

  • DrAmineDrAmine GermanyForum Coordinator

    You need to use combustion particle and allow for multiple surface reaction.

  • JeroenJeroen Member

    I have now used the combustion particle and allowed for the multiple surface reaction and specified the species mass fractions. However, the user-defined function is still not being executed.

  • DrAmineDrAmine GermanyForum Coordinator

    Add more details and add a dummy message in the udf

  • Could you please specify what details you would like me to add here? I have had a dummy message in the udf already, that's how I know it is not being executed.

  • DrAmineDrAmine GermanyForum Coordinator

    If you are already having that message in the UDF and you do not see the message, then something is wrong. Have you hooked the UDF? If yes can you reduce the whole case so that it is easy to reproduce it.

  • I have now been able to execute the UDF for my custom reaction. However, I also want to specify the heat of reaction (used in equation 16-181 in the theory guide for version 19.3) but this parameter is not present in my material properties dialog box. I am using the combusting particle and the multiple surface reactions model and I can specify the all other relevant properties such as the combustible mass fraction (which I set to 100%) and the reaction heat fraction absorbed by the solid (30%).

  • kkanadekkanade Forum Coordinator

    @Jeroen I can see each comment on this post with 'Rejected Answer'. Can you please explain in more detail about your question and why each comment is rejected.



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