Modeling vacuum suction through pipe in ANSYS Fluent

mamoody14 · February 20, 2019, 13:40

I am currently trying to model fluid flow through a pipe that is produced through vacuum suction. The amount of suction pressure would be 100 mmHg at the vacuum end. I am currently trying to use a negative gauge pressure for pressure-outlet as the boundary condition and zero pressure at the pressure-inlets for the other ends of the pipe. Is this a proper set up for ANSYS Fluent or should I approach the problem in a different way?

Also since ANSYS pressure is in gauge (Pascal) and the vacuum pressure is in mmHg or Torr, would this be considered absolute pressure and require a conversion to gauge? or do I just assume vacuum is negative gauge and use -13332 Pa? I have read some discussion on changing the operating pressure to 0, but I'm not sure the effect this would have on the system.

For some additional background on the model, I am trying to model the flow of air through different suction catheters. I want to primarily assess the amount pressure of the suction end in the different solid models during various states of suction. Additionally, while most catheters are about 40 cm in length the models are only 4 cm to mitigate the complexity of the model.

Please let me know if you have any input of need any additional information about the model.

Thank you

LuckyTran · February 20, 2019, 14:09

-100 mm Hg at the pressure outlet is the right BC to use. What pressure to use at the inlet? Well what is the pressure at the inlet of the pipe? It's probably 0, but you are the one with the pipe.

You know what this number is. Just think about it. What is the pipe inlet attached to?

-100 mmHg vacuum is also a gauge pressure. So, use the same gauge.

It depends on the equation of state whether or not the operating pressure matters or not. But you can't set 0 operating pressure and -100mmHg at the outlet because that would be a negative absolute pressure.

Gauges are actually much more commonly encountered in everyday life than people think. It's not a made up concept from CFD.

February 20, 2019, 13:40	Modeling vacuum suction through pipe in ANSYS Fluent	#1
mamoody14 New Member Marcus Join Date: Feb 2019 Posts: 1 Rep Power: 0	I am currently trying to model fluid flow through a pipe that is produced through vacuum suction. The amount of suction pressure would be 100 mmHg at the vacuum end. I am currently trying to use a negative gauge pressure for pressure-outlet as the boundary condition and zero pressure at the pressure-inlets for the other ends of the pipe. Is this a proper set up for ANSYS Fluent or should I approach the problem in a different way? Also since ANSYS pressure is in gauge (Pascal) and the vacuum pressure is in mmHg or Torr, would this be considered absolute pressure and require a conversion to gauge? or do I just assume vacuum is negative gauge and use -13332 Pa? I have read some discussion on changing the operating pressure to 0, but I'm not sure the effect this would have on the system. For some additional background on the model, I am trying to model the flow of air through different suction catheters. I want to primarily assess the amount pressure of the suction end in the different solid models during various states of suction. Additionally, while most catheters are about 40 cm in length the models are only 4 cm to mitigate the complexity of the model. Please let me know if you have any input of need any additional information about the model. Thank you

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February 20, 2019, 14:09		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	-100 mm Hg at the pressure outlet is the right BC to use. What pressure to use at the inlet? Well what is the pressure at the inlet of the pipe? It's probably 0, but you are the one with the pipe. You know what this number is. Just think about it. What is the pipe inlet attached to? -100 mmHg vacuum is also a gauge pressure. So, use the same gauge. It depends on the equation of state whether or not the operating pressure matters or not. But you can't set 0 operating pressure and -100mmHg at the outlet because that would be a negative absolute pressure. Gauges are actually much more commonly encountered in everyday life than people think. It's not a made up concept from CFD.