7_d^2_) = 22 or more;
_i.e._, Q/_d^2_=433.4
In plain language, if the number of cubic feet passing through the pipe
per hour divided by the square of the diameter of the pipe is at least
433.4, no explosion can take place within that pipe, even if the gas is
highly explosive and a light is applied to its exit.
In Chapter VI. are given the explosive limits of acetylene-air mixtures
as influenced by the diameter of the tube containing them. If we
possessed a similar table showing the speed of the explosive wave in
mixtures of known composition, the foregoing formulae would enable us to
calculate the minimum speed which would insure absence of explosibility
in a supply-pipe of any given diameter throughout its length, or at its
narrowest part. It would not, however, be possible simply by increasing
the forward speed of an explosive mixture of acetylene and air to a point
exceeding that of its explosion velocity to prevent all danger of firing
back in an atmospheric burner tube. A much higher pressure than is
usually employed in gas-burners, other than blowpipes, would be needed to
confer a sufficient degree of velocity upon the gas, a pressure which
would probably fracture any incandescent mantle placed in the flame.
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