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-   -   boundary condition of face for liquid and gas (http://www.cfd-online.com/Forums/fluent/40996-boundary-condition-face-liquid-gas.html)

 Luke May 16, 2006 12:27

boundary condition of face for liquid and gas

Hellow I have a container filled with water. The water surface is exposed to the air. The container has a heat generation in it, so the water will be heated. But the thermo flow in water surface need to be convected to the air. I do not know how to set this boundary condition. How can I set the boundary condition for the water surface.

Can somebody help me? Thx.

 Bagus Putra Muljadi May 18, 2006 03:23

Re: boundary condition of face for liquid and gas

I think you can try to set the boundary condition to INTERIOR adjacent to air surface. But in that boundary, you will have to use only 1 face used together by two continuum ( air and water )or else you find another difficulty to match the face meshing.

Or you may try to use INTERFACE but you will have to stitch the adjacent faces.

I'd rather to use INTERIOR than INTERFACE.

good luck

 Luke May 18, 2006 07:23

Re: boundary condition of face for liquid and gas

Thank you for your reply. If I use boundary condition to INTERIOR for air and water face, does the external air grid need to be establish ? I now establish only the water container grid (or mesh). Can I set boundary condition for water face which has the effect of the external air convection without establishing the air grid.

I once use the " WALL " boundary condition for water face boundary and it can set the thermal condition to " CONVECTION " which can set the " HEAT TRANSFER COEFFICIENT " and " FREE STREAM TEMPERATURE ". I ever think it is the outside convection heat transfer coefficient and outside temperature. Am I wrong?

 Bagus Putra Muljadi May 18, 2006 11:34

Re: boundary condition of face for liquid and gas

Basically, every continuums in fluent ( either it's liquid or gas ) have to be defined ( converted into grids ) if you want to observe their property distribution. Temperature, Pressure, velocity or any other properties will be observed using infinite element method as nodes in FLUENT. Unless you only interested in monitoring the liquid properties.

If you use WALL as the boundary condition, FLUENT will assume that fluid velocity adjacent to the wall is zero. I think It will be like you have a thin layer between the liquid and the gas.

I hope it helps

 Luke May 19, 2006 02:37

Re: boundary condition of face for liquid and gas

Thx for your reply~ I do not want to research the gas distribution. I just hope that I can simulate the water temperature decreased through the water face to the outside gas （PS: The water temperature is higher than outside gas）

I do not want to establish gas grid and just hope the water face has the convection effect (out of my container). Does any boundary type or setting skill can handle it?

Thank you !

 Bagus Putra Muljadi May 19, 2006 03:05

Re: boundary condition of face for liquid and gas

If that so, it is possible I guess to just use WALL as you boundary surface condition.

You can set the wall's temperature and heat coefficient factor. Theoritically this condition is incorrect , but if the wall is assumed to be very thin I think the calculation will still valid.

You can moreover set whether the solving model is steady or unsteady.

hope this helps regards bagus putra muljadi

 Luke May 21, 2006 13:45

Re: boundary condition of face for liquid and gas

THX Now I can run out the results and it seems to have the convection on the water face. But I can not confirm the results to be corrent. I will check it seriously.