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 mengyue1 March 28, 2010 07:16

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!

 sega March 28, 2010 08:57

Quote:
 Originally Posted by mengyue1 (Post 252019) 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.

 mengyue1 March 28, 2010 09:42

I mean，two gases are vapor and air....as for my case, do you have some suggestions？ thanks！
Regards!
Quote:
 Originally Posted by sega (Post 252030) 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.

 sega March 28, 2010 11:18

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.

 mengyue1 March 29, 2010 00:16

OK,thanks you all the same. i will do my best to solve this problem...

Quote:
 Originally Posted by sega (Post 252037) 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.

 Mak mak April 7, 2015 19:08

Hi Mengyue
Did you solve your problem? if yes, can you help me in simulating the heat and mass transfer in the falling liquid film over vertical surface with an air flow? (the temperature of the vertical surface is kept constant below the saturation temperature of the water)

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