There are five quantities to be dealt with, viz.:
(1) The length of pipe = _l_ feet.
(2) The internal diameter of the pipe = _d_ inches.
(3) The actuating pressure = _h_ inches of head of water. (4) The
specific gravity or density of the gas = _d_ times that of air.
(5) The quantity of gas passing through the pipe--Q cubic feet per hour.
This quantity is the product of the mean velocity of the gas in the pipe
and the area of the pipe.
The only work done in maintaining the flow of gas along a pipe is that
required to overcome the friction of the gas on the walls of the pipe,
or, rather, the consequential friction of the gas on itself, and the laws
which regulate such friction have not been very exhaustively
investigated. Pole pointed out, however, that the existing knowledge on
the point at the time he wrote would serve for the purpose of determining
the proper sizes of gas-mains. He stated that the friction (1) is
proportional to the area of rubbing surface (viz., pi_ld_); (2)
varies with the velocity, in some ratio greater than the first power, but
usually taken as the square; and (3) is assumed to be proportional to the
specific gravity of the fluid (viz.
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