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thomas February 11, 2004 14:07

Degassing Boundary Condition ????
Dear everyone, I am not a user of CFX but I would like to know something about the degassing boundary condition implemented in CFX for multiphase modelling. What kind of turbulence boundary condition imply the default degassing boundary condition of CFX. I am working on a simple bubble column with a free surface where bubble are crossing the free surface. Therefore the liquid is recirculating at the free surface. - Does the turbulent production of the liquid is set to zero in the last cel range ? mean the noudary condition is a wall where the liquid is recirculating without shear stress. - Does the turbulence terms ( k, eps (for std k-eps) or uu, vv, ww for algebraic turb method) ) at the boundary faces are set equal to the values of the last cell range ? - Is there any turbulence BC ?

hope you can gimme the informations I need ! cheers thomas

Paresh Jain February 12, 2004 00:26

Re: Degassing Boundary Condition ????
hi thomas, well me too a new user of CFX so dont know much but will try to share the knowledge whatever i have. Degassing condition can only be used when you have Gas (as dispersed phase) dispersed in liquid (continuous phase). It is generally useful in modeling cases like bubble column reactor. When u specify any boundary as degassing cindition, CFX 5.6 treats it as outlet for the dispersed fluid phase (be sure, degassing option is not for solid disperesd in fluid) and allow the gas bubbles to leave the system where as the same boundry is treated as wall for continuous phase and hence continuous phase cannot leave the domain. I think you can refer to CFX 5.6 Tutorial 16 on Air Lift Reactor for more details about Bubble Column Modeling and Degassing Condition...

If you are through then please help me in the problem i have; in my case inspite of specifying degassing condition, liquid is leaving the system!!!! (pls see the msg Degassing Condition in CFX 5.6 posted by me)

I hope this helps u..

Regards, Paresh Jain

thomas February 12, 2004 03:59

Re: Degassing Boundary Condition ????
Hi, Sorry but as I said i am not a user of CFX -> means i do not use that code at all for my simulations. But CFX is the only code I know, who has a degassing boundary condition. I am just wondering what this BC implies on the turbulence boundary condition at the free surface. Sorry to not be able to help ya. cheers, thomas

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