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Thanks for your time and effort to provide an excellent software to simulate molecular flow.

I am seeking your advise on how to determine time to reach a certain vacuum level in my chamber. I am currently running a static simulation with Outgasing load of 1e-8 mbar*l/s on all my surfaces inside the chamber and the result show the surface pressure that I am interested is at 7e-7 mBar.

I went thru your tutorial on time simulation: how do I set the outgasing so I can mornitor and determine the time that my interested surface reach 1e-5 mBar?

Thanks for your time.

Tac.

Submitted by Marton Ady 6 years ago

Hello Tac,

Thanks for your patience, was away for holidays and this is my first day back.

It's good that you've inserted a screenshot. There's one important thing to mention: profiles should be used on rectangular facets only, and according to the profile plotter, the red and blue curves are most probably on circular facets. In that case (non-rectangular facet), the actual pressure can be checked in the Facet Details window or by using textures. (This limitation exists because splitting a complex-shaped facet to 100 slices would be computationally expensive).

Now, although Molflow has a time-dependent mode, it isn't suitable for this problem. It was written to simulate fast pumpdown processes (up to a few seconds long), where outgassing from a point source (like a gas inlet) suddenly stops.

In your case, the main gas source is wall (thermal) outgassing, and since I assume pumping is constant, we're effectively looking for the time needed until your wall cleans up to outgass approximately 1.4E-7 mbar.l/s/cm2 (since pressure depends on outgassing linearly, and your simulation tells that the pressure is approx. 70 times the specific outgassing rate). This depends much more on the material time (diffusion rate, cleaning history) than the gas dynamics inside the system, and would usually follow a straight line on a log-log plot, like this example:

2017-08-22 11_25_22-Les bases du dégazage des solides correction T. Richard.docx [Compatibility Mode.png

So my conclusion would be that Molflow can't simulate what you're looking for, partly because the outgassing depends on external parameters, and partly because the beginning of the pumping happens at non-molecular flow pressures (above 1E-3mbar) which has a different dynamics than that assumed by Molflow.

If I misunderstood the problem (for example, you're looking for the pumping time after you cut a gas source), let me know!

Submitted by 55395af10d3231450f13 6 years ago

Thanks Marton for your time and a thorough response to the problem.

Tac.