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Pressure Drop Measuring Problem

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Old   June 13, 2023, 06:21
Default Pressure Drop Measuring Problem
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Mehmet
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Hi all,

I want to perform a CFD analysis to measure the pressure drop in the geometry of the volume of control. I have two questions below.


1) First of all, is the pressure drop in a duct/pipe a drop in the total pressure, static pressure or dynamic pressure?

2) I have got an unit including a fan inside. I will put this unit inside a kind of box, and there will be clearances/gaps between the unit and the box. I want to see if the air is not stucked in the gaps. I know the pressure and volumetric flow rate at the outlet of the unit when it is not installed inside the box. The pressure is 40 Pa and the volumetric flow rate is 50 CFM. So, I interpretted that the pressure drop when it is installed needs to be lower than 40 Pa so that the air can go out. I attached the picture of the geometry of the volume of control regarding the clearances/gaps between the unit and the box. The inlet of the volume of control is actually the outlet of the unit. You can see the jpeg in the attachments in which the inlet and outlet are also shown. The other outer surfaces are walls.

I know the velocity in the inlet, and the air flows to the atmospheric environment where I can define the outlet as pressure outlet with zero gauge pressure I assume.

I know how to perform the CFD analysis via Ansys Fluent, but I am not sure how I can measure the pressure drop if it is possible.

I have an idea, but it does not make much sense to me. Please, give me a better concrete approach. Here my ideas are to measure the pressure drop:
- I can measure the pressure on the inlet surface in the simulation result, then substract the pressure values at the outlet from the inlet. So, Pinlet - Poutlet = DeltaP where Poutlet=Patm

- I can measure the pressure on the inlet surface in the simulation result, then substract the pressure value at the inlet from the value of 40 Pa. So, 40 Pa - Pinlet = DeltaP

here is my email if you also want to contact or ask for the parasolid/STEP file of the geometry : mozden304@gmail.com

Thanks in advance.
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File Type: jpg Geometry.jpg (40.4 KB, 15 views)
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Old   June 13, 2023, 18:37
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Pressure drop comes in many variations. You will commonly encounter pressure drops in forms of total-to-total, total-to-static and static-to-static. Rarely do you have a static-to-total pressure drop but never anything in dynamic pressure because dynamic pressure is the bulk flow itself.


In the incompressible flow limit, the static-to-static and total-to-total pressure drops are equivalent. Unfortunately, the 1D pipe flows you see in text books teaches you this case.... where it doesn't matter...
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Old   June 15, 2023, 09:12
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Quote:
Originally Posted by LuckyTran View Post
Pressure drop comes in many variations. You will commonly encounter pressure drops in forms of total-to-total, total-to-static and static-to-static. Rarely do you have a static-to-total pressure drop but never anything in dynamic pressure because dynamic pressure is the bulk flow itself.


In the incompressible flow limit, the static-to-static and total-to-total pressure drops are equivalent. Unfortunately, the 1D pipe flows you see in text books teaches you this case.... where it doesn't matter...

Thanks for your explanation!

Do you have any idea how I can measure total to total pressure drop for incompressible flow?
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Old   June 15, 2023, 10:31
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In Fluent you create reports of total pressure. In real life you stick a probe in the flow and measure it directly. It doesn't matter if it is incompressible or compressible, it's the same.
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Old   June 16, 2023, 04:31
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Quote:
Originally Posted by LuckyTran View Post
In Fluent you create reports of total pressure. In real life you stick a probe in the flow and measure it directly. It doesn't matter if it is incompressible or compressible, it's the same.
Thanks for the intructions. I appreciate it
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