Environmental Engineering Reference
In-Depth Information
RVF
VF
RVF
VF
RVF
VF
RVF
Sluice gate
Hydraulic
jump
Flow over
a weir
Hydraulic
drop
RVF - Rapidly Varied Flow
GVF - Gradually Varied Flow
figure 2.16 Varied flow.
2.10.3.1.1 roughness
Even when new, the interior surfaces of pipes are rough. The rough-
ness varies, of course, depending on the pipe material, corrosion (tuber-
culation and pitting), and age. Because normal flow in a water pipe is
turbulent, the turbulence increases with pipe roughness, which in turn
causes pressure to drop over the length of the pipe.
2.10.3.1.2 Pipe length
With every foot of pipe length, friction losses occur. The longer the
pipe, the more head loss. Friction loss because of pipe length must be
factored into head loss calculations.
2.10.3.1.3 Pipe diameter
Generally, small-diameter pipes have more head loss than large-
diameter pipes because in a large-diameter pipe less of the water actu-
ally touches the interior surfaces of the pipe (encountering less friction)
compared to a small-diameter pipe.
2.10.3.1.4 Water velocity
Turbulence in a water pipe is directly proportional to the speed (or
velocity) of the flow; thus, the velocity head also contributes to head loss.
Note:
For a constant-diameter pipe, when flow increases, head loss
increases.
2.10.3.2 Calculating Major Head Loss
Darcy, Weisbach, and others developed the first practical equation
used to determine pipe friction in about 1850. The
darcy-Weisbach
equation for circular pipes is:
