Correct Inlet Boundary Condition at Pressure Vessel

SimonStar · December 8, 2020, 05:15

Hello everyone,

I want to simulate the stream jet out of a pressure vessel. The vessel has a small valve where the jet comes out. This valve is the Inlet of the simulation.

My problem is to find the correct inlet-boundary-condition.

The vessel has for example a dp of 10 bar to the outside. And it is large enough that the pressure inside is not doping when opening the valve for a short time.

I have two options: static-pressure-inlet-condition 10 bar or total-pressure-inlet-condition 10 bar?

Which one is the correct one?

Thank you,
Simon

LuckyTran · December 8, 2020, 19:51

Total pressure is technically more correct but you might find that it really doesn't affect the flow much whichever one you use.

SimonStar · December 9, 2020, 14:52

Thank you very much for answering, Lucky Tran. It helped me very much!

I just have one more question:

I made the total-pressure-inlet-condition in my simulation.
What I see now is that the velocity is very high right after the valve (up to 800m/s). This is normal I guess.
But the total pressure is rising in this area about 50%. Is this also normal?

What makes me thinking is the following: The total pressure normally stays at the same level (except friction issues) while the static and dynamic pressure are varying. So how can it increase right after the inlet?

Thank you again,
Simon

December 8, 2020, 05:15	Correct Inlet Boundary Condition at Pressure Vessel	#1
SimonStar Member Simon Join Date: Sep 2019 Location: Germany Posts: 51 Rep Power: 7	Hello everyone, I want to simulate the stream jet out of a pressure vessel. The vessel has a small valve where the jet comes out. This valve is the Inlet of the simulation. My problem is to find the correct inlet-boundary-condition. The vessel has for example a dp of 10 bar to the outside. And it is large enough that the pressure inside is not doping when opening the valve for a short time. I have two options: static-pressure-inlet-condition 10 bar or total-pressure-inlet-condition 10 bar? Which one is the correct one? Thank you, Simon Last edited by SimonStar; December 8, 2020 at 08:05.

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December 8, 2020, 19:51		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,747 Rep Power: 66	Total pressure is technically more correct but you might find that it really doesn't affect the flow much whichever one you use.

December 9, 2020, 14:52		#3
SimonStar Member Simon Join Date: Sep 2019 Location: Germany Posts: 51 Rep Power: 7	Thank you very much for answering, Lucky Tran. It helped me very much! I just have one more question: I made the total-pressure-inlet-condition in my simulation. What I see now is that the velocity is very high right after the valve (up to 800m/s). This is normal I guess. But the total pressure is rising in this area about 50%. Is this also normal? What makes me thinking is the following: The total pressure normally stays at the same level (except friction issues) while the static and dynamic pressure are varying. So how can it increase right after the inlet? Thank you again, Simon