BASIC PROBLEM - VACUUM help please

jpinho · September 25, 2009, 07:08

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, 11:43

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, 05:15

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, 05:33

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, 07:49

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

September 25, 2009, 07:08	BASIC PROBLEM - VACUUM help please	#1
jpinho New Member pinho Join Date: May 2009 Posts: 22 Rep Power: 17	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

October 1, 2009, 05:33		#4
herntan Senior Member YH Tan Join Date: Mar 2009 Location: Malaysia Posts: 119 Rep Power: 17	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 ? __________________ Herntan, Add Reputation if I am right

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September 30, 2009, 11:43		#2
timjm New Member Tim Maguire Join Date: Sep 2009 Posts: 19 Rep Power: 17	Can't you just specify a pressure inlet and outlet and put the realative / absolute pressures that you want at those BCs?

October 1, 2009, 05:15		#3
jpinho New Member pinho Join Date: May 2009 Posts: 22 Rep Power: 17	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

October 1, 2009, 07:49		#5
jpinho New Member pinho Join Date: May 2009 Posts: 22 Rep Power: 17	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