# Evacuate Vacuum Chamber

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 July 21, 2016, 09:27 Evacuate Vacuum Chamber #1 New Member   Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 10 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 likes this.

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

 July 22, 2016, 04:21 Floating Pressure #3 New Member   Join Date: May 2015 Location: Germany Posts: 15 Rep Power: 10 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 Senior Member   Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 11 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.

 June 20, 2017, 02:38 #5 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 Senior Member   Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 11 What is your confusion with the boundary condition of the outlet? Maybe you could describe it more specifically. @@

 June 20, 2017, 05:57 #7 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.

 Tags evacuate, fluent, udf, vacuum, x-momentum