Periodic Boundary Condition set-up challenges on mfix-23.2

MFiX How to
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#1

Dear Experts,
I want to implement a period boundary condition in all directions for a fluidized bed such that particles are fluidized with relatively uniform gas velocity and the number of particles remain the same. But I am experiencing the following challenges:

  1. Very small gas velocity and increasing gas velocity: Initially, I set-up a boundary condition for inlet gas at the velocity of 3.5m/s but observed that the outputted gas velocity was too small for the system, about 0.02m/s max. Then I removed the boundary condition and set the initial condition for fluid to 3.5m/s in the vertical direction, then I observed an increasing velocity as time passed, up to 20m/s.
  2. Loss of particles in MFIX-SQP: I set-up similar conditions for MFiX-DEM and MFiX-SQP. While the number of particles in the MFiX-DEM remained the same across simulation time, particles in the MFiX-SQP system decreased progressively.
    Please what could be the reasons for these, and how can I fix them.
    I have attached the bug reports of the two simulations. Thank You!
    one_2023-12-09T170930.790695.zip (81.3 MB)
    one_2023-12-09T171437.494666.zip (81.7 MB)
#2

Sorry for the mistake in the heading… it should be Periodic Boundary Condition

#3

I fixed the title, but note that you can edit your own posts to make corrections.

I will look at this case as soon as I get a chance! Thanks for your patience.

– Charles

#4

Noted Sir! Thank you

#5

Hello Sir,
This is a gentle reminder for you to please take a look at my challenges. Thank you!!!

#6

If you want to model a fluidized bed and gravity acts in the negative y-direction, you cannot use cyclic BCs in the y-direction. You also cannot specify both a cyclic BC and any other BC along the same planes.

The DEM case you sent has periodic BCs in all direction. I don’t see your initial velocity of 3.5 m/s, but with this setup, you are basically modeling particles free falling under gravity, so they will accelerate until they reach terminal velocity. Once particles reach the bottom of the geometry, they are recycled at the top wit the same velocity.

The SQP case has both cyclic BC in the y-direction and inlet+outlet BCs. This creates a conflict.

If you want to model a fluidized bed, remove the cyclic BC in the y-direction.

1 Like
#7

Thank you for your response. I am trying both the fluidized bed and free falling particles cases to see the one that gives me what I am looking for. Thank you!

#8

Looks like in the free fall, both the particles and fluid are recycled when they reach the bottom. Is there a way to modify this such that the fluid exit while the particles are recycled?