f 2 v² W L
E_{f} = Wh = ---------- (39)
gd
f 2 v² L
and h = -------- (40)
gd
If D represents the density of the steam or weight per cubic foot, and p
the loss of pressure due to friction in pounds per square inch, then
hD
p = --- (41)
144
and from equations (38), (40) and (41),
D v² L / 3 \
p = -------- × K | 1 + --- | (42)
72 g d \ 10d /
To convert the velocity term and to reduce to units ordinarily used, let
d_{1} the diameter of pipe in inches = 12d, and w = the flow in pounds
per minute; then
[pi] / d_{1}\
w = 60v × --- | ---- |^{2} D
4 \ 12 /
9.6 w
and v = --------------
[pi] d_{1}^2 D