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Handling Solid Volume Fraction in Gas-Solid Reaction in ANSYS Fluent

    • MS10
      Subscriber

      Hi everyone,

      I’m currently modeling a Eulerian-Eulerian gas-solid reaction (heterogeneous mechanism without UDF) in ANSYS Fluent, similar to the reactions shown in the attached image, where the solid volume fraction (ϵs\epsilon_s) is part of the reaction rate equation.

      In Fluent, I used the Arrhenius equation for the reaction rate, but I did not include a UDF for the solid volume fraction (ϵs\epsilon_s). Instead, I simply patched the solid volume fraction in the simulation.

      My question is:

      • Is this the right approach? How does Fluent handle gas-solid reactions and the solid volume fraction if it's not explicitly defined in a UDF?
      • Will Fluent automatically account for the solid volume fraction in the reaction rate, or should I have included it through a UDF?

      The results are in good agreement with experimental observations, but I’d like to confirm the validity of my approach. If possible, could you please provide any references from the ANSYS User Guide or other sources to support your response?

      Thanks in advance for your help!

       

    • Ahmed Hussien
      Ansys Employee

      When you use the Arrhenius equation for the reaction rate without including a UDF for the solid volume fraction (ϵs), Fluent does not automatically account for the solid volume fraction in the reaction rate unless it is explicitly defined in the reaction rate formula or through a UDF.

      For specific reactions and rate equations that include the solid volume fraction as a variable, you would typically need to include this in your reaction rate definition, either directly in the rate formula or by using a UDF to define how the solid volume fraction affects the reaction rate.

      Since you mentioned that your results are in good agreement with experimental observations, it suggests that your approach may be working for your specific case. However, for a more accurate representation and to ensure that the solid volume fraction is accounted for in the reaction rate, it would be advisable to include it through a UDF or directly in the reaction rate formula if the model requires it. 

      You can use the DEFINE_HET_RXN_RATE macro to define the reaction rate. You may check the documentation for more information on the implementation and examples 2.4. Multiphase DEFINE Macros (ansys.com)




    • MS10
      Subscriber

      Thank you for your response, Mr. Hussien. Yes, I believe I need to create a UDF for the solid volume fraction. I will work on it and move forward with that approach. I appreciate your suggestions.

      • d.amadi
        Subscriber

         

        @MS10 please can you contact me directly on this so we can discuss on this in detail: d.amadi@rgu.ac.uk.

         

    • d.amadi
      Subscriber

      I tried developing a UDF code for this and it is giving me errors

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