How to simulate (Configure) a gas nozzle in a vacuum chamber

- October 30, 2018 at 7:47 pm
  
  fabio.tabacow
  Subscriber
  
  Hello,
  
  I´m need to simulate a gas flow through a gas nozzle inside a vacuum chamber. In this result, I need to see the behavior of the gas jet inside this chamber (with vacuum).
  
  To do this, I made a single geometry that correspond the domain of the fluid (nozzle and the chamber), but I can´t setup the vacuum inside the chamber. In setup "folder" in Workbench, I can´t create "a material" that correspond the vacuum that will stay inside the chamber.
  
  Do anybody help me with this?
  
  Thanks a lot!!!!
- October 31, 2018 at 2:05 am
  
  Karthik Remella
  Administrator
  
  Hello,
  
  You will not be able to set-up vacuum by selecting 'materials'. To model vacuum, you will have to introduce a really low pressure in the chamber. Please elaborate more on your geometry so we can help you with the boundary condition.
  
  Thank you.
  
  Best Regards,
  
  Karthik
- October 31, 2018 at 1:36 pm
  
  fabio.tabacow
  Subscriber
  
  Hello Kremella,
  
  the geometry that I simulated is at the picture below.....
  
  When I simulated, I set the inlet pressure as 15bar (Static pressure) and the outlet pressure as -20 Torr (Static pressure). How can I be certain that the chamber has vacuum? I know that the Mach number of the results is closed than the expected, but the gas decelerate so close to the exit of the gas nozzle.
  
  If you need somenthing more to help me, ask that I will try to post here....
  
  Thank you and sorry about the English...
- October 31, 2018 at 4:43 pm
  
  Rob
  Forum Moderator
  
  You'll need to initialise and then patch pressure into certain regions. Depending on the inlet & outlet pressures you may also need to consider a transient model: ie does the vacuum chamber fill with gas?
  
  As an aside, vacuum pressure isn't within the continuum physics range so Fluent will struggle with the flow. Google the Knudsen Number to see what you need to think about.
- October 31, 2018 at 5:21 pm
  
  fabio.tabacow
  Subscriber
  
  You'll need to initialise and then patch pressure into certain regions. Depending on the inlet & outlet pressures you may also need to consider a transient model: ie does the vacuum chamber fill with gas?
  
  We made an experiment to validate the simulation model. In this experiment, the chamber stayed with a constant pressure (vacuum) of 20Torr.
  
  As an aside, vacuum pressure isn't within the continuum physics range so Fluent will struggle with the flow. Google the Knudsen Number to see what you need to think about.
  
  I will google the knudsen number again.... I think that another problem (to me) is how to input the info inside the setup....
  
  Thanks
- October 31, 2018 at 5:31 pm
  
  DrAmine
  Ansys Employee
  
  To be certain about the pressure level you need to monitor it. Again in Fluent we rely on continuum mechanics so you need to take care about the results.