Fluids

Fluids

Fluent 19.2 Population Balance Model

    • Amir
      Subscriber

      Hi all,


      I am working on population balance model to see how particle distribution changes through a continuous reactor.


      At this stage the only phenomena occurring in the reactor is particle growth rate which in fact has absolutely no effect on the number of particles. So the same number of particles has to be obtained at inlet and outlet. However, it is not the case with fluent.


      First I saw this problem was when I tried to increase the residence time and realized that the number of particles at outlet decreases with increasing residence time.

      So I thought it is because of my class definition and the number of classes is not enough to cover all possible particle in the reactor. I increased thus the number of classes testing 30, 35 and 40 classes and obtained always around 16% lost in particles.

      Below you can find the results on number of particles vs. number of classes at steady state for same condition (growth rate value, particle volume fraction and inlet velocity are all the same in these cases):



      I am using fluent 19.2 Population balance discrete method with mixture multiphase method.

      Could you please help me out with this issue?
      Any suggestions and comment is greatly appreciated.
      Amir

    • DrAmine
      Ansys Employee

      Hi,


      What about the volume fraction of the secondary phase: Is it conserved?


      It is better for debugging if you use the Population Balance Post Processing function to list all Number Density for all bin's at outlet and at inlet.

    • DrAmine
      Ansys Employee

      Another question: The particle growth in your case is due to which mechanism?

    • Amir
      Subscriber

      Hi Amine,
      Thanks for your reply.



      Actually the solid volume fraction is slightly decreased due to the lost that we have in number of particles.



      I put just the sum of all bins here to make it easier to look otherwise I list always the number of particles for all bins at inlet and at outlet.
      For your second question, it is a constant growth rate which occurs in the reactor. I would like it to be as simple as possible and did not consider any growth mechanism either by mass transfer or by reaction.



      Kind regards,
      Amir


       

    • DrAmine
      Ansys Employee

      That means your growth is not due to expansion and not to mass transfer and not reactions. This is not really physical and needs to be corrected. At least the primary phase needs to be reduced here to get into account that the mass has changed the phase.


      You said the volume fraction is lost a bit: can you then check if the new volume fraction with the averaged mean Sauter diameter do fit the number densities on inlet /outlet

    • Amir
      Subscriber

      You are right and it is due to the fact that I did not consider any mechanisms with which particles could growth.
      I run a simple test activating PBM mass transfer and the number of particles became the same at inlet and outlet.


      Thanks again
      Best,
      Amir

    • DrAmine
      Ansys Employee

      Amir you are welcome.

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