Calculating pressure required to flow at desired rate through pipe

In summary, the fireman is interested in calculating the pressure drop through a 1/4" pipe when pumping at 3-4 bbl/min. He is considering using Bernoulli's equation and adding on the friction loss through the 1-1/2" pipe to get the total pump pressure. He is wondering if he is thinking along the right tracks.
  • #1
MightyG
9
0
I have a problem which I am working on and its been a while since I did this at uni so I am after a little guidance :)

Im trying to work out what pressure will be required to flow at a specific rate through a piece of pipe, the pipe begins with an ID of approximately 1-1/2" then drops to around 1/4" and I am hoping to pump at around 3-4bbl/min through the 1/4" pipe. (126-168Gal/min)

I was thinking of using bernoulis equation and working out the pressure and velocity in the 1/4" pipe then use that work work out the pressure and velocity in the 1-1/2" pipe at the opening of the 1/4"

from this I can then add on the friction loss through the 1-1/2" to get the total pump pressure to pump through the entire length? (I am ignoring the friction loss through the 1/4" as I assume it will be negligible, its only going to be approximately 6-ft compared to approximately 2000-ft of the 1-1/2")

Am I thinking along the right tracks with this or is there another, better way to work this out?
 
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  • #2
If I am correct in this line of thought then can I say the pressure of the end of the 1/4" pipe will be the same pressure as the area it is pumping into?

In this instance the 1/4" tubing will be pumping into an area which is pressurised up to 11Kpsi, can I use this as the pressure for one half of the Bernoulli equation and us it to work back to the pressure in the 1-1/2"?
 
  • #3
Bernoulli's equation assumes the pipe does no work against the flow. In real life, friction with the walls of the pipe and viscosity of the fluid reduces pressure of a flowing fluid as the fluid flows down the pipe. The longer the distance, the more reduction there is in pressure, assuming pipe diameter doesn't change. Turbulence at transition points in pipe diameter is also going to affect the pressure. Flow will remain constant throughout the pipe (other than initial start up).
 
  • #4
As mentioned, Bernoulli's isn't going to provide the irreversible pressure loss through the pipe. Generally, the Darcy Weisbach equation is used to determine this pressure drop. The attachment on https://www.physicsforums.com/showthread.php?t=179830" goes through pipe pressure drop analysis.
 
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  • #5
Apriori calculating the thing is probably nigh impossible since you need to know all the friction and elevation change components. As a fire-person I'm interested in results so I looked up these tables for you:
http://www.elkhartbrass.com/files/aa/downloads/catalog/catalog-e-T.pdf
Page 8 has a nice table "DISCHARGE OF SMOOTH BORE NOZZLES/TIPS"...

The red flag was wanting to get >100gpm from a 1/4" pipe -- if it was 3/4" I'd say fine, go for it -- of course the above referenced tables are for hoses with nozzles that may restrict the flow a bit, but 'smooth bore' is pretty much exactly what it says.
 

1. How do you calculate the pressure required to flow at a desired rate through a pipe?

The pressure required to flow at a desired rate through a pipe can be calculated using the Bernoulli's equation, which states that the sum of the pressure, kinetic energy, and potential energy per unit volume in a fluid flow system remains constant. The equation is given as P1 + 1/2ρv1^2 + ρgh1 = P2 + 1/2ρv2^2 + ρgh2, where P is pressure, ρ is density, v is velocity, and h is height. By rearranging the equation, you can solve for the pressure.

2. What factors affect the pressure required to flow through a pipe?

The pressure required to flow through a pipe is affected by various factors, including the flow rate, pipe diameter, fluid density, viscosity, and length of the pipe. As the flow rate increases, the pressure required to maintain the flow also increases. Similarly, a smaller diameter pipe and a higher fluid density or viscosity will require a higher pressure to maintain the desired flow rate. The length of the pipe also affects the pressure, as longer pipes will have a higher frictional resistance, resulting in a higher pressure requirement.

3. How does the fluid viscosity affect the pressure required for flow?

The viscosity of a fluid affects the pressure required for flow through a pipe because it determines the resistance to flow. A higher viscosity fluid will have a greater resistance to flow, requiring a higher pressure to maintain the desired flow rate. This is because the fluid molecules in a more viscous fluid have a greater internal friction, which results in a higher resistance to flow.

4. Is the pressure required to flow through a pipe constant?

No, the pressure required to flow through a pipe is not constant. It can vary depending on various factors such as the flow rate, pipe diameter, fluid properties, and length of the pipe. As these factors change, the pressure required for flow will also change. Additionally, the pressure will decrease as the fluid moves through the pipe due to frictional losses.

5. How can the pressure required for flow through a pipe be reduced?

The pressure required for flow through a pipe can be reduced by increasing the pipe diameter, decreasing the fluid viscosity or density, or by reducing the length of the pipe. These changes will result in a lower resistance to flow, requiring less pressure to maintain the desired flow rate. Additionally, using a more efficient pipe material with less frictional resistance can also help in reducing the pressure required for flow.

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