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MrFEA May 6, 2010 08:55

Vacuum pumping
 
Hi Folks

I'm new to CFX. I'mtrying to simulate pressue inside a chamber connected to a vacuum pump. I have one intake with as wall (valve closed) and the other as outlet with mass flow. Inside is Air (ideal gas). Initial conditions of pressure is zero (relative to ambient 760 Torr).

The problem is to write boundary conditions of the outlet as the flow is a function of the pressure. I'm using a very simple equation using volumeAve(Pressure)@chamber X constant as test but flow is zero and the pressure doesn't drop. With a constant out flow it works fine.

Any ideas? Thx

FabOr June 2, 2010 05:42

Hi,
have you solved your problem?

MrFEA June 2, 2010 07:11

Quote:

Originally Posted by FabOr (Post 261341)
Hi,
have you solved your problem?

Yep, thx. Now it works fine. Waiting for benchmarking against experimental results.

FabOr June 3, 2010 08:19

Can you send me your file?
I have the same problem.
thx.
my e-mail: bguser@gmx.de

MrFEA June 7, 2010 15:14

Quote:

Originally Posted by FabOr (Post 261520)
Can you send me your file?
I have the same problem.
thx.
my e-mail: bguser@gmx.de

sorry, can't do. Hope the following will help:

1. inlet = wall
2. outlet with mass flow, as per your vacuum pump (I used mass flow as function of Pressure) - air ideal gas
3. transient simulation
4. monitor pressure (I used volume average) per simulation time. When you have enough points kill it, or let it run till end and export monitor.

Let me know how it goes. Rgds

FabOr June 11, 2010 06:17

Hi,

i used a fixed value for the velocity at the outlet, but the pressure is increasing. i donīt know really why this happen...

here are my boundary conditions
U:
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
outlet
{
type fixedValue;
value uniform (0 0 5);
}

chamber
{
type fixedValue;
value uniform (0 0 0);
}

pipe
{
type fixedValue;
value uniform (0 0 0);
}
}

p:
dimensions [1 -1 -2 0 0 0 0];

internalField uniform 100000;

boundaryField
{
outlet
{
type zeroGradient;
}

chamber
{
type zeroGradient;
}

pipe
{
type zeroGradient;
}

Maybe someone can give me a hint how to solve this problem.

thx


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