134 STEAM BOILERS, ENGINES, AND TURBINES
Here, in connection with chimney draught, a very important
matter comes in, viz. the temperature of the air outside of the
chimney.
In the accompanying table, which is taken from the
Sturtevant Company's book on " Mechanical Draught," the pressures
in inches of water-gauge, with different temperatures of the gases in
the chimney, and different temperatures of the outside air, are given,
the chimney temperatures from 200° to 500° F., and the outside
temperatures from 0° to 100°. It will be noted, from an inspection
of the table, what a very wide difference of pressure a difference in
the temperature of the outside air makes, as, say, between a cold
winter atmosphere and a hot summer one. The figures given are
for a chimney of 100 feet in height.
With the chimney temperature
at 500° F., it will be noted that with the temperature of the outside
air at 30°, the water-gauge produced is 0-73 inches, while with the
same chimney temperature, and with an outside temperature of 100°,
the water-guage is only 0'534, or a reduction of 0'196, sufficient to
furnish the pressure for driving the gases through the chimney itself.
With a chimney 200 feet high, the above figures would be doubled,
and there would be a difference such as would easily occur, say, in
Canada, or other countries subject to wide variations of temperature,
of 0*392 inches water-gauge.
TABLE XV. ,
Table of Peessubes in Inches of Wateb-Gauge, with Difpebent Tempebatubbs in Chimney and Outside Atmosphbbb.
Tempera-
