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Old   August 11, 2011, 18:06
Default Simulating a Vacuum Pump
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I would like to simulate the flow in a chamber that is being pumped on by a scroll pump. The pressure inside the chamber is supposed to stay a constant 0.3 atm, the gas that is sucked out by the pump is being replace through inlets. Currently I am using stagnation inlets set to -0.7 atm and a pressure outlet set to -0.9999 atm (reference pressure 1 atm). Is this the most correct way to do this simulation?
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Old   August 15, 2011, 01:04
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several suggestions:
- since the pressures everywhere are going to be around .3atm absolute, set the reference pressure to that value - will aid convergence
- then outlet will be 0atm relative to your new reference pressure (assuming this is what you really want)
- not sure about your stag.inlet since you need to know the stagnation conditions - you might not have compressible flow, so it is easier, otherwise need total pressure, total temperature - see Help topic Modeling Physics > Setting Up Physics > Setting Types > Boundary Types Reference > Stagnation Inlet
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Old   October 19, 2016, 10:35
James Willie
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Hi Marisa,

I was wondering if you found a solution to your problem then? I am modeling a similar flow for a vacuum pump and i am using CFX as the solver and the inet is set to 'Opening' and i have given the gauge pressure there which is negative and the outlet is also set to 'Opening' and the gauge pressure there is about 6mbar. I am using Ideal gas and the flow is compressible due to tiny gaps we have inside the pump housing.

In your case did it mean that your mass flow at the inet was negative and that at the outlet was positive? What about your velocity vectors? I am doing unsteady with the immersed solid method in CFX to include the rotation of the solid rotors inside the pump housing. But when i plot my velocity vectors i see the direction towards the inlet predominantly. Is this normal?


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