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Old   September 20, 2012, 08:56
Default CFX air bubbles in water
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Jennifer S
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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?

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Old   September 24, 2012, 21:55
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Glenn Horrocks
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Please upload your CCL, output file and/or an image of your geometry.
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Old   September 27, 2012, 06:51
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Jennifer S
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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. air_bubble1.zip

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Old   September 27, 2012, 07:50
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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
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Old   September 27, 2012, 08:09
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Jennifer S
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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.
air_bubble1.zip

result_comparsion_pressure.jpg

result_velocity_fluid with air bubbles.jpg

result_velocity_fluid without air.jpg

Best regards
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Old   September 27, 2012, 18:41
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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.
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Old   October 3, 2012, 06:14
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ali
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I can send you the instruction of simulation if you have an Email address
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Old   October 3, 2012, 07:11
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I do not give out my email address on the forum. Post it on the forum instead.
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