[amin.z]

Hi,

I have a bubbly flow with very small bubbles. Range of the bubbles diameters is between 100 to 500 micron. I've simulated the flow by constant bubble size, 300 micron. Now, I wanna solved the domain by various bubbles diameter and I wonder how can I write a UDF in order to calculating bubbles diameter through the flow field!
Which parameters can changing the bubbles diameter!?

Thanks in advanced

[CeesH]

Hi Amin,

I am guessing you use Euler-Euler with a population balance model for the bubble size? In that case, it depends on which way you implement the pop. balance. If you go for a class method, FLUENT should output the number of bubbles in each size class (although I am not 100% sure on how this works, I never used the method)

If you use the (faster) QMOM method, it's a bit more tricky - but you don't need a UDF. Anyway, in QMOM you do not have direct access to the bubble sizes; dividing moment-3 by moment-2 does give the sauter mean diameter which of course is a first indication of size. As far as I know, this is also the diameter used when calculating drag and so on. The other moments do carry information about the distribution of bubble sizes, but you need to reconstruct the distribution function. There is a tool in FLUENT that does this under the 'report' tab. Do keep in mind that there is no unique solution, there is an infinite amount of functions that will give you the same moments but that are not equal. So, the reconstruction is an approximate bubble size distribution. The more moments you use (4, 6 or 8), the more accurate it gets, but it is never exact.

Best,
Cees