10

APPLICATION OF THE LAWS OF HYDRAULICS

FIG. 7.

upon the sides (the walls of the furnace) (Fig. 7). The confining
boundary upon the bottom may be present or not. In the same
manner, a stream of water may be confined by walls below and

upon both sides, while
its upper surface is
entirely free. In a
similar way the gase-
ous stream has to be
confined upon the top
and the two sides,
while upon the bottom
its surface is entirely
free.

It would reveal a
serious error in this
theory, if, for exam-
ple, the breeching, or
smoke flue, common to four boilers was found to be completely
filled with gases without regard to the number of boilers which
were in service. This, however, will not be the case. In a
correctly proportioned smoke
flue the free lower surface of
the gaseous stream will be
found in the neighborhood of

the bottom A A (Fig. 8). If
the volume of the gases flow-
ing decreases to one-fourth its
former volume, the thickness
of the stream decreases two
and one-half times <1} or to 0.40
its former thickness, and the
lower free surface of the gases
will be found at the level BB]
within the space A ABB, no
circulation of the gases will
be found. (2)

(1) Where 2.5 = V4^ as may be seen further on, p. 40.

(2) This statement is not absolutely correct, as eddy currents will exist in
the space A ABB due to the cooling effect of the walls upon the flowing stream
of heated gases.