Flow velocity through pipe

[Engprofile]

Hi,
This is a relatively simple one I believe, but I have not had to do it before.
I am trying to work out what the velocity will be through a 150mm pipe which is 45m long and has an RL difference of 5m from top to bottom.
The pipe is pressumed full with 100mm of head above the top of the pipe. The pipe is a drain pipe which will be used to drain coal spillage (Slurry). I wont to make sure the pipe is the correct size.
I believe the Bernoullie equation can be used for this? V=Sqrt(2gh)? how do I take into account friction loss?
The only pressure is that of the small static head (100mm on the pipe at the top). I am assuming the pipe will be full.

 

[Engprofile]

Or should I be using the manning equation:

Q = (1.486/n)*A*(R^2/3)*S^0.5
Where: Q = flow in cfs
A = Area in sq ft
R = hydraulic radius in feet
( for a circular pipe R = D/4 )
S= slope of the hydraulic gradeline in feet/foot

For a standard galve pipe what would be the friction feet/100ft?

 

[zdas04]

The FIRST assumption in Daniel Bernoulli's derivation of his famous equation is that there is no friction (followed by the flow being incompressible, steady with time, and isenthalpic). You can't account for friction in that equation. People will probably follow this post with something called the "Modified Bernoulli Equation" which is taught in some big name schools by some seriously sloppy engineering professors. It purports to include friction as a plug value and it produces results which have a poor match to field data.

Assuming the pipe will be full is a risky assumption. Take a look at thread124-177112 for that equation.

I'm not sure you have Manning copied down right, but I'm on the road and don't have my books. You might also look at Darcy Weisbach.

David

 

[katmar]

I believe you are going about this the wrong way. If your assumptions are all correct (flooded inlet and pipe full) and the liquid were pure water you would get a flowrate of around 260 m[sup]3[/sup]/hour, or a velocity close to 4 m/s. If your liquid is not being replaced at exactly this rate your assumptions would soon be invalid.

This is a common problem in the sewage piping sector. Through years of experience they have determined the minimum slope required to make the piping self-cleaning. If you have a non-pumped system you are in the same situation.

Somehow you will need to determine the self-cleaning slope and velocity. This is not something I have done myself, so I cannot guide you. Once you have this, and you know your average and peak flows, you can determine the pipe size required. If you have insufficient slope, or you have low points in the piping, it will just be a matter of time until the pipe blocks.

Katmar Software - Engineering & Risk Analysis Software

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[BigInch]

Manning & Darcy works for coal sluries?
I never would have guessed.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus