How do i set the BC of vacuum chamber

crazytrex · July 28, 2020, 05:03

Hi~ i'm trying to simulate a vacuum chamber which has only outlet on fluent.
Chamber pressure drops to about to 1 torr at atmospheric pressure by dry pump.
I design only the chamber and outlet line(small pipe shape), no dry pump module.

I want to see the time for pressure drop.

I set the pressure-outlet boundary condition with specific pressure, then chamber average pressure going to same with pressure-outlet pressure at the first time step even i set the small time step.

Which outlet boundary condition is suitable for this simulation???

karachun · July 28, 2020, 05:19

You should manually initialize the domain with atmospheric pressure before run. Don't use hybrid initialisation.

evcelica · July 28, 2020, 12:21

That's one heck of a pump you have. Put the pump curve in, it does not just instantly pull perfect vacuum at the pump inlet.
Make sure you have continuum flow, not molecular flow. CFD can't model 0 absolute pressure. Check your Knudsen number, at some absolute pressure you won't have continuum pressure anymore. and you CD is invalid, or will blow up.

July 28, 2020, 05:03	How do i set the BC of vacuum chamber	#1
crazytrex New Member Jihong Chung Join Date: Jun 2017 Posts: 1 Rep Power: 0	Hi~ i'm trying to simulate a vacuum chamber which has only outlet on fluent. Chamber pressure drops to about to 1 torr at atmospheric pressure by dry pump. I design only the chamber and outlet line(small pipe shape), no dry pump module. I want to see the time for pressure drop. I set the pressure-outlet boundary condition with specific pressure, then chamber average pressure going to same with pressure-outlet pressure at the first time step even i set the small time step. Which outlet boundary condition is suitable for this simulation???

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July 28, 2020, 05:19		#2
karachun Senior Member Join Date: Nov 2015 Posts: 247 Rep Power: 12	You should manually initialize the domain with atmospheric pressure before run. Don't use hybrid initialisation.

July 28, 2020, 12:21		#3
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,190 Rep Power: 24	That's one heck of a pump you have. Put the pump curve in, it does not just instantly pull perfect vacuum at the pump inlet. Make sure you have continuum flow, not molecular flow. CFD can't model 0 absolute pressure. Check your Knudsen number, at some absolute pressure you won't have continuum pressure anymore. and you CD is invalid, or will blow up.