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Old   November 13, 2001, 01:49
Default phase contours
  #1
gorman
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Hi,greetings to you. I am modelling a gas lift technology using single string and oil-CO2 model.I haved tried using algebraic slip and VOF method but my tube is always filled with the primary phase only. I have tried varying the oil inlet and gas inlet with both defined as pressure inlet or velocity inlet but it does not work as well.Please advice..thank you

gorman
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Old   November 13, 2001, 04:57
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Atholl
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Have you set your volume fractions at the inlets correctly?
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Old   November 13, 2001, 05:24
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hvn
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Is your tube vertical or horizontal ?
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Old   November 13, 2001, 11:41
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cheong
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would the volume fraction in the boundary condition panel is as same as in the initialize panel? is there any way to calculate the volume fraction with the information of superficial velocity of gas and liquid phase?
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Old   November 13, 2001, 12:19
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Atholl
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Using the VOF scheme for two phase flow, I set the volume fractions at the two inlets as 1 for one inlet and 0 for the other, the order of which is dependant of what you have set as the primary phase, this way you don't have to calculate the volume fractions manually. You should get the two phases appearing nicely after that (assuming you have got convergence!!)
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Old   November 14, 2001, 00:04
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gorman
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yes, I have already set te volume fraction as 1 for one inlet and 0 for another inlet.My primary phse is oil and gas in secondary phase.But the tube seems to have filled with only the primary phase all the time.Is there a "time step" mistake when i display the phase contours?
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Old   November 14, 2001, 08:10
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Atholl
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You should see both phases when you display density, viscosity or volume fraction contours. However, it may be that there is a problem somewhere with your setup - go through everything again to look for errors. If you are running unsteady, then are you iterating for enough time steps for both phases to actually appear in the domain?
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Old   November 14, 2001, 10:06
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gorman
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dear hvn,

my tube is vertical 2000m height,I had assume atmospheric pressure at 2000 m and oil was injected upwards at bottom with 10 psig and CO2 was injected horizontally into the tube at 5 psig. Gas injection took place from an opening at 250 m from the bottom.Please advise.
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Old   November 14, 2001, 10:23
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hvn
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Hello,

If I understand well what you want to simulate, the VOF method isn't the rigth method because it is used for stratified flows or someting like that. You should use the lagrangian method. In fluent, it is the dispersed particle method (DPM).

When you perform a cfd study, you must choose the method following what you want to simulate and not the contrary.

Normally in the Fluent user's manual, they speak about the limitation of VOF method.

I hope that could help you.

HV
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Old   November 18, 2001, 22:47
Default Re: phase contours
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gorman
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hi,

i have successfully see the phases as advised. Thanks, anyway, i have a doubt here. since we have already input our initial value in boundary condition under define, do we need to input again those value in solve>initialize before we perform iteration? what if these values differ with those in define>boundaries condition. thanks
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Old   November 18, 2001, 22:50
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  #11
gorman
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hi, I admit that VOF model could not be run under my model, anyhow, i use algebraic model and it is possible with pretty good iteration shown. Do you think algebraic slip is proper in modelling gas lift technology such in my case?

Thanks
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