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-   -   Gas-solid modeling (Fluidized Bed) (http://www.cfd-online.com/Forums/fluent-multiphase/122842-gas-solid-modeling-fluidized-bed.html)

nezam.aziz@gmail.com August 29, 2013 06:40

Gas-solid modeling (Fluidized Bed)
 
Dear all,

I'm working on simulation of gas-solid contact process, starting from a Bubbling Fluidized Bed (BFB) to a Fast Fluidized Bed (FFB).
But I have a problem with loss of mass within my system, while I'm assured that there is no mass flow rate out of my system from outlets.

For example, a bed which is fluidized around its minimum fluidization velocity (U_mf). Mass of solid disappears around 90% after 2-3 seconds of flow time. This rate would be lower while I increase the fluidization velocity.

Example: Considering a 2D problem,
- bed (W=0.3, H=0.5)m
- solid particles (ro=3000 kg/m3) (d_p=200e-6 m)
- Gas phase (air)

V_mf~=0.05 m/s
U_terminal~=1.5 m/s
V_gas=0, 0.1 m/s, 0.5 m/s and so on

Eulerian-Eulerian Model
(Both laminar and turbulent methods were tested)
Solid phase, granular fluid: Granular viscosity-> Gidaspow; Granular Bulk Viscosity-> Luen et al; Interaction of phases-> Symlal-Obrien

if I filled in the bed e.g. 50% with solids... and run the fluent in transient mode (which the time step is dt<dx*dy) dx&dy=0.01m

*** The mass of solid in the bed, start decreasing after a while and approaching zero while the flow time increases.

So, the question is "what is the source of this degradation in mass of solids"
could it be generated due to wrong model, or the mesh size and time step should be more fine?!

Additionally, I followed a simulated problem in an article which the writers compared the results with experiments (mesh size and time step were implied by that paper)... I also have missing in solid mass!!!

Thanks in advance for reading my long comment ;)


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