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

In summary, when pressure difference is 7 bars and the diameter is 25.4 mm, the air leaving the outlet will travel at a velocity of about 50 meters per second.
  • #1
apekattenico
6
0
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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  • #2
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
 
  • #3
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.
 

1. What is the equation for calculating flow rate through a pipe using pressure drop?

The equation for calculating flow rate through a pipe using pressure drop is known as the Bernoulli's equation. It states that the pressure drop (ΔP) is equal to the flow rate (Q) multiplied by the fluid's density (ρ), the gravitational constant (g), and the height difference (Δh) between two points in the pipe. It can be represented as ΔP = ρgΔh.

2. How do I measure the pressure drop in a pipe?

To measure the pressure drop in a pipe, you will need a pressure gauge. This device can be attached to the pipe at two different points to measure the pressure difference between them. The difference in pressure will give you the value for ΔP, which can then be used in the Bernoulli's equation to calculate the flow rate.

3. Can the diameter of the pipe affect the flow rate?

Yes, the diameter of the pipe can affect the flow rate. According to the Venturi effect, as the diameter of a pipe decreases, the fluid's velocity increases. This means that for a given pressure drop, the flow rate will be higher in a smaller diameter pipe compared to a larger diameter pipe.

4. What other factors can affect the flow rate through a pipe?

Apart from the pressure drop and pipe diameter, other factors that can affect the flow rate through a pipe include the fluid's viscosity, the pipe's length and roughness, and any obstructions or bends in the pipe. These factors can create additional resistance to the flow of fluid and affect the overall flow rate.

5. Is there a way to increase the flow rate through a pipe?

Yes, there are a few ways to increase the flow rate through a pipe. One way is to increase the pressure drop by using a pump or compressor. Another way is to decrease the pipe's diameter, as mentioned in the Venturi effect. Additionally, increasing the smoothness of the pipe's interior surface can also help reduce resistance and increase the flow rate.

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