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Old   September 20, 2010, 21:38
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Hi, just wondering is there anybody in here who has done a multi phase simulation for liquid liquid separation. gas liquid is ok i've got problem for liquid liquid, cant set an interface level and also get a big mass imbalance, running for a lomg time still is not converging, checked everything mesh,....no change in results. it is a flow inside a vessel and the concept is separation.
I would appreciate any any help.
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Old   September 21, 2010, 06:31
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I have not done it but it should be possible. But it may take a while to find the right settings so it converges and is accurate, so keep at it, you are on the right track.
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Old   September 21, 2010, 13:42
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I agree with Glenn, it should be possible. Guess you have to use inhomogenous flow field, otherwise you will not get separation.
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Old   September 22, 2010, 22:07
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Thanks Glen,
it is going too slow, havent reached to a stable condition yet and there is still a big mass imbalance. I've started with a 0.005sec time step, with increasing it during the run , residuals are below 1xe^-4 but courant number goes to order of hundred ...around 134, wondering should i reduce the time step?

Thanks joey ,
yes as it is an oil water separation, im using a particle modle for interphase transfer.
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Old   September 23, 2010, 02:36
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Quote:
it is going too slow
Sounds like the error is with the user, not the simulation. The user needs more patience. CFD can be a very laborious process.

You have not described your simulation - steady or transient? What physical models? What fluids? What size geometry and initial conditions?
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Old   September 23, 2010, 03:52
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Glenn,
I think User is patient has been working on this for weeks.
The case is a two phase, oil/water separator horizontal vessel. vessel ID is 3.048m and lenght is 12m but using symetery plane ive modeled 1/4 of the vessel. running a transient simulation, oil as continuse phase(0.96 volume fraction),and water as dispered phase with droplet diameter 10mm. for boundary conditions, mass flow rate at inlet and static pressure at outlets, oil outlet at top and water at bottom. i needed to set interface level at 700mm from bottom of the vessel, so as initial condition i considered this level at 730mm to start with and let it goes down to 700mm. I've set homogenous turbulance model, particle model for interphase transfer...
It is running for days, once it got close to very small mass imbalance but again went up dramatically.....
I would appriciate any help.
Also i can send you the*.def file.
(Operating pressure is 20.5 bar but i dont think... )
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Old   September 23, 2010, 18:23
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I would put the residuals in the results file to see if any regions of high residuals exist. Any idea what happened when the imbalances suddenly got worse - did a big glob of stuff reach an outlet or something like that?
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