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-   -   Problem of air bubbles in water. Please help !!! (http://www.cfd-online.com/Forums/fluent/47197-problem-air-bubbles-water-please-help.html)

xc February 2, 2008 03:44

Problem of air bubbles in water. Please help !!!
 
Dear All,

I need to examine the behavior of air bubbles in a water flow (open channel). Please advise on the following questions.

(1) The bubbles are around or less than 5 mm (in diameter) and the air VOF is less than 20%. The Eulerian mixture model should be the best option. Is this right?

(2) The Eulerian mixture model can only set ONE diameter for the dispersed phase. Correct? Can UDF be used to set more than one bubble size?

(3) The bubble cannot shrink or grow in the Eulerian mixture model. Yes or no?

(4) There is no way to consider the bubble coalescence in the Eulerian mixture model. Right?

(5) If DPM is used, can the bubbles coalesce and become bigger one?

Eagerly waiting for your expert inputs. Thank you so much for your help.

xc


xc February 4, 2008 20:27

Any two-phase experts? Please. *NM*
 

lurk February 5, 2008 20:37

Re: Problem of air bubbles in water. Please help !
 
1)if gravity or another external force is important you ned to use a per phase eulerian model. This do not use the mixture density to calculate the momentum equations. 2) you can define ex 3 phases and two of them are bubbles. 3 and 4 if you are gonna have coalescing of bubbles you need to use the population balance model. see fluent documentations. 5) no clue, but the dpm is highly computational expencive ond it can't simulate a real system with that high consentration of bubbles. and i am not an expert so i anm not compleatly sure of this, but the fluent doc is very good on this. -lurk

xc February 5, 2008 21:31

Re: Problem of air bubbles in water. Please help !
 
Hello Lurk,

Thank you very much for your answers, which are so helpful. Regarding the bubble coalescing, where is the population balance model you mentioned? Is it a new model? I tried but could not find anything about it. By the way, my version is 6.3.36. Best regards.

xc

lurk February 6, 2008 06:05

Re: Problem of air bubbles in water. Please help !
 
The population balance is a extra addon in fluent 6.3. and it is licensed. so you have to ask the responible for the license . I think it's posible to implement it by UDF's but it's difficult. if you have the ducumentation for fluent 6.3 it's a ovn user guide. -lurk


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