Hi

I want to know how to create vacuum in FLUENT. I have given the operating pressure as 0 Pa. But I dont think it is creating a vacuum that way as I could see the recirculation of air. Can anyone help me with this?

Thanks,

Shanti

maybe you could try turning off the flow equations in the solution control panel. Also, be sure you have zero gauge pressure in all your boundary conditions

Hi

Thanks for your reply. But I am solving for the interface tracking of a fluid. Won't turning off the flow equations affect that?

Thanks,

Shanti

Navier Stokes equations which are solved in Fluent are not valid in very low pressures.

Hi

When I deselected the flow equation, vacuum has been created. But I am not able to study the forces acting on the walls. Is there any way I can study that?

Thanks,

Shanti

can you define the 'low pressure' range. How low is that low?

If your Knudson number is greater than 1/10, then Navier-Stokes is not valid.

There is no specific range for pressure. I just want to create vacuum.

[mvee]

Hi

Did you create vacuum and able to solve the NS equations? How?

Thank you

[RodriguezFatz]

No, he wasn't. No one can do that. Fluid equations without any fluid just don't make any sense at all.

[mvee]

Hi RodriguezFatz

You are exactly correct. Perfact vacuum can not be modelled. I have following questions:

(1) Can we model low pressure 1e-5 Torr and solve it by compressible flow equations?
(2) If the pressure of 1e-5 Torr is not possible then what is the minimum pressure we can go?
(3) How Knudson number is related to compressible flow?

Your reply is very much helpful to me.

Thank you
Mvee

[RodriguezFatz]

To all your questions:
Knudsen number is the mean free path for atom/molecule collisions divided by the size "L" of your domain. It means: How many collisions occur, when a particle travels through your domain (Kn is the inverse of that number). If the number of collisions is large enough the gas can be considered to be a continuum.

Thus, you can answer these questions only if you know L.

[sumeet kotak]

Originally Posted by RodriguezFatz

To all your questions:
Knudsen number is the mean free path for atom/molecule collisions divided by the size "L" of your domain. It means: How many collisions occur, when a particle travels through your domain (Kn is the inverse of that number). If the number of collisions is large enough the gas can be considered to be a continuum.

Thus, you can answer these questions only if you know L.

Hello RodriguezFatz sir,

I am simulating Electron beam physical vapor deposition system (EB-PVD) for coating of evaporant on substrate. For improvement of purity of coating, I required vacuum inside the chamber. The amount of vacuum required at least 3e-5 mbar using (0.005 Pascal) (practically measured value).

so can u help me how can i create vacuum inside the chamber...???
how to set operating pressure in operating condition dialogue box and pressure outlet pressure in boundary condition dialogue box....???

0.005 Pa is measured using vacuum gauge, practically, by performing experiment.

[RodriguezFatz]

Please read the posts of this thread and you will see that it is absolutely senseless to use Fluent for this case.

[sumeet kotak]

thanks for replay sir...
sir in knudsen no. how to calculate mean free path length.. ie. distance between two particle just before collision?

[RodriguezFatz]

Have a look at:
http://en.wikipedia.org/wiki/Mean_free_path
Take the first formula of section "mean free path in kincetic theory" and put in your gases density and collision cross section!
Although I don't expect that your particle distribution will be maxwellian...