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-   -   CFX air bubbles in water (http://www.cfd-online.com/Forums/cfx/107220-cfx-air-bubbles-water.html)

Jennifer September 20, 2012 09:56

CFX air bubbles in water
 
Hello,

I am just beginning to learn to use CFX. I have some problem of setup a simulation with air bubbles in water in a simple horizontal pipe.

I have followed the setup for a tutorial for Ansys chapter 18 "Gas-liquid flow in an airlift reactor". However, the CFX solver just doesnt run AND it return to code 1. Is anyone can help me with this problem? :)

Best Regards

ghorrocks September 24, 2012 22:55

Please upload your CCL, output file and/or an image of your geometry.

Jennifer September 27, 2012 07:51

1 Attachment(s)
Hi Ghorrocks,

I have changed the setting and now the simulation run normally.
I have assigned two points in the pipe in order to measure the pressure change and compare the results for fluid with air bubbles and fuild without air bubbles. However, the results shows that the pressure level is much much higher (about 20 times)when the fluid have air bubbles than the fluid without. It seems strange, right? because the fluid is only contain air as bubles up to 5 % of its volume. (I have defined 0.05 for air and 0.95 for fluid in "volume fraction")

I have defined the fluid velocity value for 5.6m/s and I don't know whether I should define the velocity of air, since the only information I have is the fluid have air bubles and I don't know about the velocity for air in this case. (I tried to define the air velocity to 0 and the solver would not run).

P.s I have upload the output file and geometry. Attachment 15944

Best regards

ghorrocks September 27, 2012 08:50

I have no idea if that result is strange - it is your simulation. But the multiphase flow could well significantly affect the pressure field so I would not say it is impossible.

But in general this is an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

Jennifer September 27, 2012 09:09

4 Attachment(s)
Hi Ghorrocks,

I have changed the setting and now the simulation run normally.
I have assigned two points in the pipe in order to measure the pressure change and compare the results for fluid with air bubbles and fuild without air bubbles. However, the results shows that the pressure level is much much higher (about 20 times)when the fluid have air bubbles than the fluid without. It seems strange, right? because the fluid is only contain air as bubles up to 5 % of its volume. (I have defined 0.05 for air and 0.95 for fluid in "volume fraction")

I have defined the fluid velocity value for 5.6m/s and I don't know whether I should define the velocity of air, since the only information I have is the fluid have air bubles and I don't know about the velocity for air in this case. (I tried to define the air velocity to 0 and the solver would not run).

P.s I have upload the output file, image for geometry and images for results.
Attachment 15947

Attachment 15948

Attachment 15949

Attachment 15950

Best regards

ghorrocks September 27, 2012 19:41

If the bubbles create a strong enough updraft that the main cross flow gets impeded then I can see why the pressure drop across this thing increases greatly.

eng_norouzi October 3, 2012 07:14

I can send you the instruction of simulation if you have an Email address

ghorrocks October 3, 2012 08:11

I do not give out my email address on the forum. Post it on the forum instead.


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