Dear Professor,
1 I need to use MFIX TFM to simulate a 2D bubbling fluidized bed with a diameter of 0.06 m and a height of 1.45 m. The initial bed height is 0.16 m, the particle mass is 0.8 kg, and the true particle density is 3800 kg/m³. My particle diameter is 0.000805 m The material is iron ore.. The inlet gas velocity at the bottom is 1.474 m/s. The initial solid volume fraction of the bed is calculated as:(0.8/3800)/(3.14×0.03×0.03×0.16)=0.46。
2 Boundary conditions: mixed wall; no-slip for the gas phase and partial-slip for the solid phase.
3 I set the packed bed void fraction to 0.33, 0.38, and 1−0.46 = 0.54 for the ore phase, but in all cases the bed expansion is excessively high, and the simulated images do not match those from the high-speed camera. Could this be because I did not set a distributor plate or screen at the bottom?If so, how should I model it if it is an ultra-fine mesh? And if it is like a drain plate with 300 small holes of 0.2 mm, how should I set that up? 038k.mfx (9.9 KB)
The same case was with me as distribution plate at bottom plays a critical role in bubbling & hydrodynamics of the bed. Also see mesh grid resolution.
Don’t miss to see a single, high-velocity jet that causes a large central bubble and excessive expansion over bed.
"Thank you for the advice regarding the distributor and grid resolution. Currently, I am using a 20x320 grid with a mesh size of about 3 times the particle diameter ($3 d_p$).
Regarding the mesh: Is 20 cells in the lateral direction sufficient for a 60mm diameter bed, or should I refine it? Also, should I use a graded mesh to refine the area near the inlet?
Regarding the distributor: I am using a ‘Semi-permeable’ internal surface at the bottom. Could you provide some guidance or a recommended range for determining the ‘Fluid permeability’ and ‘Internal resistance coefficient’ to properly simulate a physical distributor?
Any suggestions or references for these settings would be greatly appreciated."
Your observation is correct, 20 cells looks likely insufficient for a 60mm bed and may be for the distribution system. while in my case i used impermeable surface type instead of semi-permeable because i need solid wall but your case is perfect fit for semi-permeable IS if you aim to use porous membranes and filters.
