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-   -   BASIC PROBLEM - VACUUM help please (http://www.cfd-online.com/Forums/fluent/68607-basic-problem-vacuum-help-please.html)

jpinho September 25, 2009 06:08

BASIC PROBLEM - VACUUM help please
 
Hello,

I am getting confused since I have tried several ways to solve this basic problem.

I have a chamber (imagine rectangle 2D) where I want to simulate vacuum. So, in one of the sides I set a boundary as exaust-fan, and define pressure.

Even with a unsteday case I got divergences problems as the pressure and temperatures drop below minimums. Please help.

It is a simple problem and I am not getting it.. I just want to get a plot pressure over time... to know how long will take to have a determined pressure..


thanks
jpinho

timjm September 30, 2009 10:43

Can't you just specify a pressure inlet and outlet and put the realative / absolute pressures that you want at those BCs?

jpinho October 1, 2009 04:15

timjm,
thanks for your suggestion.

I dont think is the best approach since in the reality there is no inlet to the chamber.
The air just flows out.. If I a creat a pressure inlet BC I am giving a new source of air into the system which does not fit my problem.

Regards
jpinho

herntan October 1, 2009 04:33

I never use exhaust fan BC before. can you post the picture of ur setting?
i was wondering if u need to input fan curve into the exhaust fan?

have u set ur operating pressure as 0 ?

jpinho October 1, 2009 06:49

When you use exhaust fan BC, you have to define the pressure jump. You can set it constant or if you have the pump curve, you can relate the pressure with the velocity in a more realistic way.

However, I didnt get proper results because there is no convergence in my solution. I have serched on the forums and I didnt find vacuum simulations cases explained.

I would like to do a transient simulation to plot over time, ther pressure inside a chamber with a vacumm pump extracting the air.

Regards
Jorge Pinho


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