Fluids

Fluids

Reversed Backflow, Continuity divergence

    • despinosam
      Subscriber

      Hello,


      I've been struggling with the simulation of a fluidized bed in 3D. I have simplified my geometry to what is shown on the first picture. At first I run it with the whole area at the bottom as the inlet, however my case should have a distributor which has the geometry shown in the second picture. The simulation with the whole bottom as the inlet has run quite well so far, but when I change the geometry with the distributor I keep getting reversed backflow on a hundred faces or more. And even if I start to running it as a steady state case I get to a floating point exception. I really don't know what to do to get this problem to work, I've tried improving my mesh but it doesn't work either.



    • DrAmine
      Ansys Employee

      Can you please show the whole geometry where you how experience the issues. Reversal flow at outlet itself is not an issue if it is happening in the beginning or due to physical re-entrainment.

    • despinosam
      Subscriber
      The back flow happens on the red zone shown on the picture I uploaded before. My geometry is basically a cylinder, except for bottom where I imprinted the geometry of the distributor.
    • DrAmine
      Ansys Employee

      Yeah the red zone is defined as pressure outlet right? Still not able to understand the distributor story? That is why please the whole geometry.

    • despinosam
      Subscriber


      This is inlet geometry. It represents a distribution plate that we have on our real reactor to allow the gas enter more uniformly and not all at once which is what happens when there are no holes. As my goal is to compare simulation results to experimental ones I tried to do my geometry as close as to my real reactor. Hopefully this will make you understand it much better.


       


      Thanks, 


      Daniela

    • despinosam
      Subscriber

      each hole has a 0.0015m diameter, and the cylinder diameter is 2in.

    • DrAmine
      Ansys Employee

      Can you post the boundary conditions used in your model? Are you accounting for energy transfer? Are you enabling gravity?

    • despinosam
      Subscriber

      I am not using energy equation. 


      Boundary conditions: 


      Outlet: atmospheric pressure 


      Inlet: 0.2 m/s for gas phase, 0 for solid phase


      Walls: no slip for both phases

    • Raef.Kobeissi
      Subscriber
      Try to use the outflow bc or extend the length of the pipe.
    • DrAmine
      Ansys Employee
      Do not use Outflow only if you make your pipe longer. Is the secondary solid phase patched on the whole system? Do not forget to enable gravity and provide an operating density either equal to zero or the the one of air outside.

      Reversal flow is not a KO criterion if you read carefully again what I wrote earlier.
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