Boundary condition in DEM simulation

MFiX How to
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#1

hello all
I’m simulating heat transfer in a simple rectangular fluidized bed, and I have two question regarding boundary conditions. Can you assist me with these?
1-I’ve set the outlet as a pressure outlet, but during my simulation, particles tend to leave the domain. How can I prevent them from exiting and ensure they stay within the domain?
2- How can I set the wall heat loss coefficient to be specific number like 300 W/m^2.k for the side walls?
Thank you.

fig
fig444×723 119 KB

zhou_heattransfer_2023-09-11T161653.976096.zip (30.5 KB)

#2
  1. My recommendation is to move the outlet plane up. There is a significant bed expansion that reaches the top of your domain. It is possible that if you start with a less packed initial condition it may help. You can force particles to not cross the outlet plane by setting bc_po_apply_to_des(2) = .False. from the Advanced pane. Click the “+” icon on top of the keyword table, start typing “bc_po_apply_to_des” in the search box, select the " bc_po_apply_to_des" from the list. Enter “2” for the BC index (because this applies to BC#2), and uncheck the “Value” box so it becomes “False”. Click on “Update key”. This will prevent particles from leaving the domain but it may create a plug if you are above terminal velocity, so I am not sure this is a good option for you.

image
image1172×867 95 KB

  1. MFiX doesn’t use a heat transfer coefficient, it is applying a temperature gradient in the form dT/dn + h(T-Tref) = c.
2 Likes
#3

Thanks a lot for your help! I’ll give your suggestion a try and see how it works. I really appreciate your response.

#4

The fluidization velocity is too large, using bc_po_apply_to_des(2) = .False. will create a plug. I think your best option is to move the outlet up.

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1 Like
#5

Oh, I understand now. Thanks!