Fluidized bed with internal baffles--Negative void fraction detected and DT < DT_MIN

MFiX How to
#1

Hi MFIXers, I tried to simulate a fluidized bed with internal baffles using TFM model. The geometry is generated in Solidworks. I used MFIX to do the meshing and build up the model.

However, I always got the error “Negative void fraction detected” and “DT<DT_MIN”. I would very appreciate if you could help me check my .mfx file and point out the potential errors. Thank you!
case33_2023-03-28T144701.294100.zip (1.4 MB)

#2

Your stl file was not included, so I used geometry.stl instead. Maybe your STL normals are pointing in the wrong direction, please check and attach the stl file.

https://mfix.netl.doe.gov/doc/mfix/22.4/html/faq.html#how-to-verify-flip-stl-file-facet-normals

#3

Hi Jeff, here is my .stl file. I think the STL normals are fine.
case2.STL (60.6 KB)

#4

Hi Jeff, I am sorry to interrupt you. Do you receive the .stl file? I have checked the normals and they ar fine. I have bothered by this error in this simulation case for a while. Would you please help with checking .mfx and .stl files? Thanks!

#5

Yes I see the STL file but I have not had a chance to take a look. Thank you for your patience. MFiX users are encouraged to help each other too.

#6

Hi lyang88, The code complained that the solids pressure (P1) doesn’t converge, so changed the solids viscous stress model to Lun, made the grid in the y direction finer, the code can run without problem to about 0.1s. Please check if it works for you for a longer simulation time.
For_Lei.zip (62.9 MB)

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1 Like
#7

Hi Yupeng, thanks for your kind help! I think it can work now.