Math question...

**TwoSeven** · 23rd February 2005, 18:05

How do you calculate how much liquid will flow thru a pipe ?

I have a pipe that is 5mm long and an i.d. of 2.5mm I need to work out how much liquid (assume water for now) will flow thru at normal air pressure and temp.

I need to know the formula, not the answer.

**jrandom** · 23rd February 2005, 18:17

Google for 'fluid dynamics'.

Here's something from the list returned:

http://www.jgsee.kmutt.ac.th/exell/T...AddPhysics.htm

Should give you what you need.

**Hitcher** · 23rd February 2005, 18:48

Originally Posted by TwoSeven

How do you calculate how much liquid will flow thru a pipe ?

I have a pipe that is 5mm long and an i.d. of 2.5mm I need to work out how much liquid (assume water for now) will flow thru at normal air pressure and temp.

I need to know the formula, not the answer.

That's not a pipe, it's a pigeon's leg ring!

At "normal air pressure" (presumably 1 atmosphere) no liquid will flow through. The pipe is sufficiently small for capilliary attraction to be significant in a low pressure application. This will become more significant as the viscosity of the liquid increases (more of a problem for oil than water). In practical terms this pipe is so short the formula you should be using would be to calculate fluid flow through an orifice.

I am busy rummaging for my agricultural engineering notes. I used to know all of this stuff and it should be lying around here somewhere...

**jrandom** · 23rd February 2005, 18:52

Originally Posted by Hitcher

That's not a pipe, it's a pigeon's leg ring!

Yes, but the first chapter of this semester's textbook starts with "Consider a liquid pigeon's leg..."

**Hitcher** · 23rd February 2005, 18:58

Found it. You need to use the extended Bernoulli equation:

Rather than type if for you, follow this link. It looks the same as in my old notes.

http://www.engineersedge.com/fluid_f..._bernoulli.htm

But I still think that the pipe is too small (length and diameter) for any calculations based on this formula to be valid.

**Jantar** · 23rd February 2005, 19:25

Originally Posted by Hitcher

Found it. You need to use the extended Bernoulli equation:

But I still think that the pipe is too small (length and diameter) for any calculations based on this formula to be valid.
[/font]

You are quite right, the pipe IS too small. Liquid will only flow through due to capilliary action unless it is driven by a pressure or head differential.

Liquid will flow from an area of higher pressure to one of lower presure through a small pipe. In this case where you state normal air pressure and temp, I assume that means the liquid is discharging to air. It still needs a head to drive the liquid into the pipe.

The velocity at which liquid will travel into and through this pipe is given by the formula V = sqrt(2*G*H)
Where V is Velocity measured in m/s
G is Gravity at 9.81 m/s^2
H is the effective head (how far is the intake below the surface of the liquid) measured in m

Once you know the velocity, then the total flow is simply velocity * cross sectional area of the pipe. Roughness co-efficient and viscosity can be neglected as the total pipe length is less than 5 times its diameter.

I hope this helps.

**TwoSeven** · 23rd February 2005, 21:50

Cheers folks..

Pigeon leg ring ? orifice ?? liquid pigeons leg ?

You mean the person measuring the pigeons ass forgot it was still full of shit

**ching_ching** · 23rd February 2005, 22:20

Originally Posted by Jantar

You are quite right, the pipe IS too small. Liquid will only flow through due to capilliary action unless it is driven by a pressure or head differential.

Liquid will flow from an area of higher pressure to one of lower presure through a small pipe. In this case where you state normal air pressure and temp, I assume that means the liquid is discharging to air. It still needs a head to drive the liquid into the pipe.

The velocity at which liquid will travel into and through this pipe is given by the formula V = sqrt(2*G*H)
Where V is Velocity measured in m/s
G is Gravity at 9.81 m/s^2
H is the effective head (how far is the intake below the surface of the liquid) measured in m

Once you know the velocity, then the total flow is simply velocity * cross sectional area of the pipe. Roughness co-efficient and viscosity can be neglected as the total pipe length is less than 5 times its diameter.

I hope this helps.

Fucking Hell!!! :spudwhat: