How to find the flow rate trough a pipe using pressure drop

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To determine the flow rate through a pipe using the pressure drop of 7 bar and a diameter of 25.4 mm, the velocity can be approximated with the formula V = sqrt(2*g*dp/dens), where g is gravitational acceleration, dp is the pressure drop, and dens is the fluid density. The relative roughness of the steel pipe is crucial for calculating the friction factor, which affects flow rate. The length of the pipe (50 meters) is relevant when sizing a pump for fluid transport. For accurate calculations, users should ensure unit consistency and consider additional resources for formulas related to compressed air. Understanding these factors will help in estimating the air exit speed from the pipe.
apekattenico
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Hi,
I want to know how high the flow rate trough a pipe is (outlet), but I only now the pressure difference (0.7MPa or 7 bar), and the diameter of the pipe.

At what speed (or for that matter volume) does air leave a pipe when the pressure difference is 7 bar, and the diameter is 25.4mm?

If it makes any difference it's steel pipes, of about 50 meters. (But I don't feel that info is neccesary)

Thanks a lot in advance!
 
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For a first approximation you can use this formula for the velocity.

V = sqrt(2*g*dp/dens)

where

g = gravitation acceleration
dp = pressure drop
dens = density of fluid in the pipe line.

Make sure all of your units cancel correctly.

If it makes any difference it's steel pipes,...

Yes, it does make a difference because of the relative roughness of the pipe. This value is needed in order to calculate the correct friction factor.

..of about 50 meters. (But I don't feel that info is neccesary)

This would be necessary if you where trying to size the pump needed to pump the fluid the 50 meters.

Hope that helps.

Thanks
Matt
 
CFDFEAGURU said:
For a first approximation you can use this formula for the velocity.

V = sqrt(2*g*dp/dens)

where

g = gravitation acceleration
dp = pressure drop
dens = density of fluid in the pipe line.

Make sure all of your units cancel correctly.

EDIT: I honestly don't see what formula for speed you used. What is g doing there?


Yes, it does make a difference because of the relative roughness of the pipe. This value is needed in order to calculate the correct friction factor.



This would be necessary if you where trying to size the pump needed to pump the fluid the 50 meters.

Hope that helps.

Thanks
Matt

Excellent answer!

I guess I could've phrased my question a little better.

At what speed does the air leave the outlet when you know it holds 7 bars in the pipe?

Thanks a lot for the quick response :)

(Anyone know a page where I can find general forumlas regarding compressed air?)
Thanks in advance.
 

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