How many gallons per minute?

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Question from Diane:

HI
I have a natural water spring and I am trying to determine how many gallons per minute will flow in an 8" pipe? I know one gallon is 231 cubic inches and V=nr2h - so if i had one foot of 8" pipe it would hold 2.6 gallons but I'm looking for the flow rate of how many gallons per minute? Thanks for your help.

Hi Diane.

You are deep into the world of engineering and physics, rather than mathematics here. My understanding is that you need more information about the pressure drop through the pipe (that is, you need to know the pressure going in and the pressure going out) and the viscosity of the spring water (probably 0.01 Poise is good enough as an approximation).

Try looking at this Hyperphysics page for more about the physics involved, including an online calculator. Note that this won't work if the flow is turbulent, it only works for laminar flow.

Good luck,
Stephen La Rocque.

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