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CFX Modelling 3 Phase flow with particle transport fluid and particle transport solid

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Old   February 18, 2020, 10:44
Default CFX Modelling 3 Phase flow with particle transport fluid and particle transport solid
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Amon
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Hi docs,
I'm trying to model a 3-Phase Flow using CFX. Air (continuous fluid) is entering the domain on the first inlet, water (particle transport fluid) is entering from the second, they combine and get out from a common outlet. Air contains dust in form of Al2O3 aluminum oxide particles (particle transport solid). Every phase (air, water and Al2O3) has a mass flow rate of 1 kg/s. You can take arbitrary particle diameter distributions.

What physically happens is that the water particles will collide with dust (Al2O3), stick together, and that will clean up the air, that's a dust collector. If I have a dust particle mass flow rate of 1 kg/s at the inlet, I expect to have something like 0.1 kg/s at the outlet, since the water will collect most of those solid particles.

I modeled this, seems like the solution is working, when I want to calculate the mass flow rates of water and dust I'm having this error:

"ERROR Mass flow of fluid 'Dust' is not available in domain 'Default Domain' and cannot be calculated on geometry 'Exit'."

I defined at the tab "Particle Behaviour" with Particle Mass Flow = 1 kg/s for both dust and water, I cannot get them at the outlet. All other parameters like velocities and pressures seem to be working, but the particle mass flow rates of water and dust cannot be calculated, and I don't know why.

Seems like a complex problem. Let's formulate it this way:
"How can we calculate the mass flow rates of particle transport fluid and particle transport solid in a three phase flow?"

Any help or suggestion is appreciated
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Old   February 19, 2020, 13:03
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There could be numerous reasons why you don't find any mass. Where do you get this error?
But first, open the .out-file and look at the bottom for the summary of mass balances. There, for all boundaries you can find how much goes in and how much goes out and it also tells you if it is in balance (in=out).
Can you find these lists and share them and give us your thoughts about it?
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Old   February 24, 2020, 15:28
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Quote:
Originally Posted by Gert-Jan View Post
There could be numerous reasons why you don't There, for all boundaries you can find how much goes in and how much goes out and it also tells you if it is in balance (in=out).
This is only true for the "Continious fluid" phase, that is in our case the "air". But what about the "Particle transport fluid (water)" and the "particle transport solid (dust)"? I define both of those two mass flow rates from Fluid Values -> Define particle behaviour -> Particle behaviour (checked) -> Particle Mass Flow -> Massflow rate = 100 kg/s. But this mass flow does nowhere appear in the continuity equation.

Even if you inject 100 kg/s dust and 100 kg/s water, the total inlet is = 1+1 =2 kg and the exit is 2 kg/s. I mean the total inlet = total exit holds only for the continuous phase, the mass flow rates of the "particle transport fluid" and "the particle transport solid" phases are simply "ignored".

This report says, they are simulated by CFX, but how?
https://www.ansys.com/-/media/ansys/...ering-dust.pdf
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Old   February 24, 2020, 18:16
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When I do a calculation with particles (Dispersed Particle Transport Fluid=Lagrangian Particle tracking), I get a list where the particles end up at the end of each iteration they are injected. This intermediate report (in the .out-file) looks like:

================================================== ====================
Particle Diagnostics
================================================== ====================
+--------------------------------------------------------------------+
| Particle Fate Diagnostics |
+--------------------------------------------------------------------+
| Particle type | Fate type Particles
+--------------------------------------------------------------------+
| Powder mixture | Entered domain : 6250 |
| | Collected on walls : 233 |
| | Exceeded distance limit : 6017 |
+--------------------------------------------------------------------+

So, in this typical case 233 particles reach a wall, and 6017 are still floating around in the domain somewhere.
When I stop the calculation, I get the following list of mass flows:


================================================== ====================
Particle Diagnostics
================================================== ====================
+--------------------------------------------------------------------+
| Particle Mass Flow Summary |
+--------------------------------------------------------------------+

Powder mixture
Particle Injection Region Nozzle 1 9.3540E-02
Particle Injection Region Nozzle 2 9.2676E-02
Periodic pair Side 1 -2.2659E-02
Periodic pair Side 2 2.2659E-02
Wall 1 -1.5452E-02
Wall 2 -1.3472E-04



So in my case, CFX gives me all the information I need.

Bottom line: look for Particle Diagnostics in the output file.
What does this tell you?
Can't it be that all your particles are still floating around?
What does your postprocessing program show you?
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Old   February 25, 2020, 15:55
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================================================== ====================
Particle Diagnostics
================================================== ====================

+--------------------------------------------------------------------+
| Particle Fate Diagnostics |
+--------------------------------------------------------------------+
| Particle type | Fate type Particles |
+--------------------------------------------------------------------+
| Water | Entered domain : 100 |
| | Left domain : 100 |
+--------------------------------------------------------------------+
| Dust | Entered domain : 100 |
| | Left domain : 16 |
| | Exceeded integration limit : 84 |
+--------------------------------------------------------------------+



================================================== ====================
Particle Diagnostics
================================================== ====================

+--------------------------------------------------------------------+
| Particle Mass Flow Summary |
+--------------------------------------------------------------------+

Water
Exit -1.0000E-01
InletWater 1.0000E-01

Dust
Exit -1.6000E-02
InletAir 1.0000E-01


Thanks, I looked at the "Fluid Flow CFX_046.out" File and got this result. That possible says to me, I have entering dust mass flow rate as 0.1 kg/s and exiting dust as 0.016 kg/s. That says %84 of the dust has collided with the water particles and formed droplets, is this really what it means?

I have the CAB (Cascade Automisation Model) particle model checked. The out file is here:

https://wetransfer.com/downloads/896...5205142/896483
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