Evacuate Vacuum Chamber

Sara28 · July 21, 2016, 09:27

Hello Everybody,

is it possible to simulate a chamber with just an outlet to see how the pressure changes by evacuating the chamber with a pump?

I know the mass flow at the outlet. But when i say there is a specific Outlet mass flow the simulation got an error in the X-momentum.

Is it even possible, because simply say i take mass out of the chamber so the density and pressure changes. How can i do that? Or is it impossible due to mass imbalances? I´m not afraid of UDF if it´s necessary.

I hope you understand what i wanted to explain, my English is not the best.
As Fluid i use air.

Kind regards

Sara28 · July 21, 2016, 10:02

When i use velocity at outlet, no pressure change occurs.

What else can i try?

Sara28 · July 22, 2016, 04:21

So it´s me again.

I modeled a Volume surrounded by walls and one outlet. At the outlet i defined a mass-flow-inlet with my mass-flow by changing the direction vector so it flows out of the domain. Then i took air and in the material panel ideal gas for density (compressible). As operating pressure i choose floating pressure. For inital floating pressure i use 101325 Pa, my pressure at the beginning. I do transient calculation. When i start the calculation i got an error: Divergence detected in AMG solver: pressure correction.

What am i doing wrong?

SJSW · June 16, 2017, 08:43

I think that it is not necessary to use floating pressure.
Maybe you can try a high-pressure chamber and mass-flow-inlet with negative mass flow?

--
Sorry, my fault.
You could try mass-flow-inlet with negative mass flow and floating pressure since there is no pressure-referenced boundary condition.
--
The mass-flow-inlet could not be negative.
Then I suggest
1. Using floating operating pressure and mass-flow-inlet with the outward direction since the mass flow could not be negative.
2. Using velocity inlet with negative velocity and proper absolute pressure(maybe 0?).

Kirk.H · June 20, 2017, 02:38

hello,
I want to simulate the process of evacuating a chamber with just an outlet in FLUENT. But I am confused about the boundary condition of the outlet. Would you give me some advice? Thank you so much!

SJSW · June 20, 2017, 05:13

What is your confusion with the boundary condition of the outlet?
Maybe you could describe it more specifically. @@

Kirk.H · June 20, 2017, 05:57

Because this chamber is vacuumed by the vacuum pump, the velocity and the pressure of boundary are always changing. And I want to calculate the time to reach the specified pressure in the chamber.

July 21, 2016, 09:27	Evacuate Vacuum Chamber	#1
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	Hello Everybody, is it possible to simulate a chamber with just an outlet to see how the pressure changes by evacuating the chamber with a pump? I know the mass flow at the outlet. But when i say there is a specific Outlet mass flow the simulation got an error in the X-momentum. Is it even possible, because simply say i take mass out of the chamber so the density and pressure changes. How can i do that? Or is it impossible due to mass imbalances? I´m not afraid of UDF if it´s necessary. I hope you understand what i wanted to explain, my English is not the best. As Fluid i use air. Kind regards Kirk.H and GILLL like this.

July 22, 2016, 04:21	Floating Pressure	#3
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	So it´s me again. I modeled a Volume surrounded by walls and one outlet. At the outlet i defined a mass-flow-inlet with my mass-flow by changing the direction vector so it flows out of the domain. Then i took air and in the material panel ideal gas for density (compressible). As operating pressure i choose floating pressure. For inital floating pressure i use 101325 Pa, my pressure at the beginning. I do transient calculation. When i start the calculation i got an error: Divergence detected in AMG solver: pressure correction. What am i doing wrong?

June 16, 2017, 08:43		#4
SJSW Senior Member Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 12	I think that it is not necessary to use floating pressure. Maybe you can try a high-pressure chamber and mass-flow-inlet with negative mass flow? -- Sorry, my fault. You could try mass-flow-inlet with negative mass flow and floating pressure since there is no pressure-referenced boundary condition. -- The mass-flow-inlet could not be negative. Then I suggest 1. Using floating operating pressure and mass-flow-inlet with the outward direction since the mass flow could not be negative. 2. Using velocity inlet with negative velocity and proper absolute pressure(maybe 0?). Last edited by SJSW; June 20, 2017 at 06:15.

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July 21, 2016, 10:02		#2
Sara28 New Member Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 11	When i use velocity at outlet, no pressure change occurs. What else can i try?

June 20, 2017, 02:38		#5
Kirk.H New Member Join Date: Jun 2017 Posts: 2 Rep Power: 0	hello, I want to simulate the process of evacuating a chamber with just an outlet in FLUENT. But I am confused about the boundary condition of the outlet. Would you give me some advice? Thank you so much!

June 20, 2017, 05:13		#6
SJSW Senior Member Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 12	What is your confusion with the boundary condition of the outlet? Maybe you could describe it more specifically. @@

June 20, 2017, 05:57		#7
Kirk.H New Member Join Date: Jun 2017 Posts: 2 Rep Power: 0	Because this chamber is vacuumed by the vacuum pump, the velocity and the pressure of boundary are always changing. And I want to calculate the time to reach the specified pressure in the chamber.