Pumping Head
Pumping Head
(OP)
I need some general help checking what head the pump will be up against for a fluid with a sg of 1.55 through a 3/4" line - 325 ft long, 10 ft elevation. Can someone give me a formula for doing this?
I have done this a long time ago but forgot how.....
I have done this a long time ago but forgot how.....





RE: Pumping Head
RE: Pumping Head
hf = f (L/D) V2/2g
hf = frictional resistance in ft of fluid
L = length of pipe in ft
D = average internal diameter of pipe in ft
V = average fluid velocity in f/s
g = acceleration of gravity, 32.17 ft/s2
f = dimensionless friction factor, there are graphs for its estimation based on the dimensionless Reynolds' number. Re = (density)(velocity)(diameter)/(absolute aka dynamic viscosity) in consistent units.
Losses on valves and fittings are expressed either as equivalent pipe lenghts, or by h = k.V2/2g
k values are tabulated.
To these friction head losses, you must add any static pressure differences as well as any difference in heights.
RE: Pumping Head
RE: Pumping Head
If you look at the last line of 25362's response, you'll see that density is catered for thus:
"To these friction head losses, you must add any static pressure differences as well as any difference in heights."
Regards,
Brian
RE: Pumping Head
RE: Pumping Head
The friction head will be more for pumping molasses than it would be for water due to the fact that molasses has a higher viscosity than water (at ambient temperatures). This would be accounted for in the determination of the Reynold's number, which in turn is used to determine the friction factor f as outlined in 25362's post.
However, an increased density of the fluid does not necessarily mean an increase in head loss, provided the "kinematic" viscosity (equal to the absolute viscosity divided by the density) of the two fluids is equal.
In short, you have to determine the friction factor for your fluid. To do this, you'll need to find/determine the viscosity.
Cheers,
CanuckMiner
RE: Pumping Head
There's another equation, simpler, but valid only for laminar flow (Reynolds number < 2000) under pressure in circular pipes, called the Hagen-Poiseuille law.
Head loss hL=32v(L/gD2)V
Where
v = kinematic viscosity
L = length of pipe
g = gravitational acceleration
D = inner diameter of pipe
V = average velocity of fluid
Everything else, valves, fittings, static head, etc. still has to be considered the same as if you were using Darcy Weisbach. That's digging back to my university fluid dynamics though, these days I usually just calculate friction losses with software.
RE: Pumping Head
Get a copy of "Crane's Flow of Fluids" and use the formulas and graphs therein.