cτ = 27690 foot-pounds.
(2)
| Fig. 99. |
The equation of continuity, which expresses the condition that in steady motion the same weight of fluid, W, must pass through each cross section of the stream in the unit of time, is
GΩu = W = constant,
(3)
where Ω is the section of the pipe and u the velocity of the air. Combining (1) and (3),
Ωup/W = cτ = constant.
(3a)
Since the work done by gravity on the air during its flow through a pipe due to variations of its level is generally small compared with the work done by changes of pressure, the former may in many cases be neglected.