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Old   March 28, 2010, 08:16
Unhappy about VOF and evaporation
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Hi guys, i am confused about my work now.
the question is: water falls down along a vertical heated tube (falling water film) to cool the tube, meanwhile, air is forced into the tube from the bottom of the tube to enhance the evaporative effect of the falling water film.
i use VOF model to track the interface of gas phase and liquid face, as for evaporation, i found udf in some website, but it just involves water and steam, so how i write udf to introduce the mass of vapor to the air, i mean, in my case, there are two kinds of gas in the gas phase, how i treat them using VOF? or maybe VOF dosen't work for this case?
thanks a lot!
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Old   March 28, 2010, 09:57
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Quote:
Originally Posted by mengyue1 View Post
Hi guys, i am confused about my work now.
the question is: water falls down along a vertical heated tube (falling water film) to cool the tube, meanwhile, air is forced into the tube from the bottom of the tube to enhance the evaporative effect of the falling water film.
i use VOF model to track the interface of gas phase and liquid face, as for evaporation, i found udf in some website, but it just involves water and steam, so how i write udf to introduce the mass of vapor to the air, i mean, in my case, there are two kinds of gas in the gas phase, how i treat them using VOF? or maybe VOF dosen't work for this case?
thanks a lot!
Regards!
VOF is isothermal and does not involve the energy equation.
Makeing VOF work with evaporation is no easy task.

Besides including the energy equation you will have to introduce temperature dependend mass sources / sinks for your different phases.
Which are only active on the interface.

Why do you have two gases? You just talked about water and air.
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Old   March 28, 2010, 10:42
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I mean,two gases are vapor and air....as for my case, do you have some suggestions? thanks!
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Originally Posted by sega View Post
VOF is isothermal and does not involve the energy equation.
Makeing VOF work with evaporation is no easy task.

Besides including the energy equation you will have to introduce temperature dependend mass sources / sinks for your different phases.
Which are only active on the interface.

Why do you have two gases? You just talked about water and air.
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Old   March 28, 2010, 12:18
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Well, I can't give you some useful suggestion.
Be aware that this is a very complex problem and you will have to take very much phyical laws into account.

There is a rather complex discussion in the OpenFOAM-forum about VOF and evaporation. This may be not applicable to FLUENT - as you don't have access to the code - but I'm sure you can learn a lot of things about what the problems are when facing evaporation.
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Old   March 29, 2010, 01:16
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OK,thanks you all the same. i will do my best to solve this problem...

Quote:
Originally Posted by sega View Post
Well, I can't give you some useful suggestion.
Be aware that this is a very complex problem and you will have to take very much phyical laws into account.

There is a rather complex discussion in the OpenFOAM-forum about VOF and evaporation. This may be not applicable to FLUENT - as you don't have access to the code - but I'm sure you can learn a lot of things about what the problems are when facing evaporation.
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