Darcy Weisbach equation - units?
Darcy Weisbach equation - units?
(OP)
All,
If I use the Darcy Weisbach equation for head loss in a pipe, the resulting units are feet. I have always assumed this to be feet of water. But if I am calculating head loss on a fluid with an SG of 0.8, is the head loss still in feet of water? Or is in feet of water/0.8?
Thanks
EE
If I use the Darcy Weisbach equation for head loss in a pipe, the resulting units are feet. I have always assumed this to be feet of water. But if I am calculating head loss on a fluid with an SG of 0.8, is the head loss still in feet of water? Or is in feet of water/0.8?
Thanks
EE





RE: Darcy Weisbach equation - units?
Pump head curves are also given feet, which is the same for any fluid being pumped.
RE: Darcy Weisbach equation - units?
EE
RE: Darcy Weisbach equation - units?
Energy loss per unit length of pipe due to friction can vary between fluids, or even with the same fluid, as that is related to the fluid's viscosity and other system parameters, such as velocity and pipe roughness. So 10 ft of head loss pumping water might come at a velocity of 3 ft per second, whereas 10ft of head loss with gasoline might be at 5 ft per second.
This is also why a net positive suction head required for a pump of 22.3ft basically does not change no matter which fluid is being pumped (within reason), but the actual suction pressure required to supply that head can and does vary with the fluid's specific gravity, viscosity and vapour pressure.
RE: Darcy Weisbach equation - units?
Thank you for taking the time to explain that.
EE
RE: Darcy Weisbach equation - units?
Pump differential head curves do not need to be adjusted for fluid either (again within reason). Pumps will lift all fluids to the same head as indicated on the pump curve. What can change with the fluid is likely to be the power required to do so, as volumetric flowrate x mass density x head, is obviously proportional to the density of the fluid. The heavier the fluid, the more power required.