three phase simulation in fluent
 

Hi
I want to simulate a three phase flow in a tank with rushton impeller
I use eulerian model
primary phase: water
secondary phase : granular sludge (2% volume fraction)
other secondary phase : air (4%volume fraction and bubbles with 0.0005 m diameter)
can you help me for choose appropriate solution method and under relaxation factors for converging?

Hi Mona,

That is quite a complex model you want to use, with quite a lot of parameters you can tune. What is the size of your sludge particles?

Some general tips
- make sure your mesh is sufficiently fine, to accurately capture power number and turbulence details: so make multiple meshes, and see if the propeties converge with time for single phase. This does not guarantee the mesh will work perectly for multiphase too, but it's a good starting point
- think about which forces you need. Scouting literature can help a lot! In general, for the gas phase in stirred tanks typically only drag suffices, lift does not affect a lot, and neither does virtual mass (some publication on this are by Ranade for example). For drag, I recommend universal drag with the brucato correction. You may have to tune correction strength.
For the granular phase, I'm not well read into that. So you will have to search some literature, to find which models are most suitable!

Best
Cees

Hi cees

Size of sludge particles is 1 mm diameter.
Generated mesh for single phase is fine, but for tow or three phase didnt converge.
As you said, I got some literature by ranade and these are usefull
Thanks a lot

A typical problem with multiphase is that people want to do too much at once - enable all the forces, it must be better, that kind of stuff.

I'd say start simple. If single phase works, try 2-phase. If that works, try 3-phase. Start with 1 force (drag) and add additional ones if needed, but only after checking which ones you expect have a significant effect. Other problems that might occur: check the outflow velocity of your gas sparger compared to your grid size. I've seen some situations in which the sparger was really a jet, and that may be difficult to simulate (you may need small timesteps to keep the courant number low/large underrelaxation factors if you run steady)

I do it and for single and 2-phase works good. But for three phase after 100 itrate I see that residual for continuty become 10000!!!!
I try to change under relaxation factors and do it again
Thanks again

Hello again
I changed under relaxation factors and converged residuals. Counturs of velocity and phasee-volume fraction show good agreement with literaturs. Now I want to use PBE model for gas phase. Do you have any information about this model?

Hi Mona,
Don't you need to consider free surface ? and is it your PhD thesis ?
i want to model bubble column and atmosphere air above it. i don't know whether i should consider a 2 phase or a 3 phase model (water : primary phase , air bubbles and atmosphere air as secondary phase ) . any help will be appreciated. thanks