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Full text of "The Flow Of Gases In Furnaces"

THE THEORY OF JETS                               65
When ^ = 0, that is to say, when the jet enters cold air, the
formula becomes
77-V
H~2g
V2
and as y designates the head h the formula becomes
# = 273
h     tm
a proportion which has already been given on page 31.
The application of the theory of gaseous jets to the open-
hearth furnace is illustrated in Fig. 23, which shows a model of an
open-hearth furnace, within the heating chamber of which a cur-
rent of colored kerosene is circulated. As may be seen in the cut,
all of the heating chamber, except that portion occupied by the
bath, is filled with the kerosene. Here, or more exactly, in all
that portion of the heating chamber which is below the sills of the
gas ports, water remains, and there is no means by which it can
be forced out of the heating chamber.
The presence of the water clearly demonstrates the most
important defect of the open-hearth furnace and many other
similar furnaces. The hot gases enter and leave the furnace
immediately below the roof, and all that portion of the heating
chamber below the level of the sill of the ports and above the steel
notch or tapping hole, a distance which varies in actual furnaces
from 0 m 50 to 1 m 50, is outside of and below the direct current
of the gases.
In the model it is clearly shown that the bath of the open-
hearth furnace is in a pocket, from which the cooled gases cannot
flow naturally and where they remain, accordingly, practically
immobile. In order to expel these cooled gases from the hearth,
as well as to mix the heated gases forming the flame, the gas and
the air are directed downward upon the hearth, and as they enter
the heating chamber at a high velocity, the phenomenon of the
gaseous jet is utilized in forcing their current downward to a depth
equal to that of the furnace below the port sills, or down to the
level of the tapping hole. In European furnaces the entry velocity
of the gas and air varies between 12 and 18 meters per second,
while the gas velocity in some American furnaces is as high as 50
meters per second.
If the theory of the gaseous jet is correct, all open-hearth