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Diffusivity calculation

    • Henry Steven Fabian Ramos

      Dear CFD Colleagues,

      I write on behalf of my research team at UAlberta to inquire about the calculation of the mass diffusivity coefficient.

      We are aware that Fluent is able to calculate the mixture mass diffusivity natively using various methods (one of them being the Kinetic theory method).
      Our goal is to take said diffusivity and modify it mathematically according to our needs within a UDF macro (to determine, for instance, the effective diffusivity or the dispersion coefficient in a porous bed).
      However, once we select the 'user-defined' method, it seems that we are required to code the full formulation of diffusivity from scratch.

      Thus, our question is: Is there a way to still obtain the diffusivity calculated by Fluent whilst using the 'user-defined' method? (I.e. invoke the value calculated by Fluent within a DEFINE_DIFFUSIVITY macro, so that we can modify it afterwards and return an updated diffusivity).

      Thank you for your assistance in advance.

    • Rob
      Forum Moderator

      I don't think you can. Most of the built in models are overwritten by UDFs, so a lot of the returned values are not available as UDF macros. 

    • Henry Steven Fabian Ramos

      Dear Rob,

      Thank you very much for your reply.
      It's unfortunate that can't be done. We believe that Fluent should include preassembled routines for calculating properties using the in-built methods, so that we can easily invoke them at our convenience in a UDF environment.

      Thank you again.

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