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Full text of "The Flow Of Gases In Furnaces"

COMBUSTION AND BOILER SETTINGS                323
velocity carries them through the bank of tubes and the hole in
the baffle. In fact it is very probable that the failure of the
baffle at this point was due to the continual impinging upon it of
the hot gases. The chilled current of gas flowing down around
the tubes of the boiler would also tend to force the hot gases,
flowing out from below the arch, against the baffle. After passing
through the break in the baffle a portion of the hot gases will
tend to rise into the upper portion of the first and second pass,
while the balance will be carried down by the current of cooler
gases flowing down the second bank of tubes and will pass under
the second baffle. They will then immediately rise to the outlet,
passing up the space between the second baffle and the third bank
of tubes, then crossing the tube bank near the top, under the rear
drum.
The explanation of this action is very simple. Anyone who
has sat by a window on a cold day knows that the air chilled by
contact with the window drops to the floor, and that the velocity
of the air current is appreciable, although the difference in tem-
perature between the inside of the room and outside of the building
is comparatively small, say, from 20 to 40 C. The same
phenomenon, except that the current of air rises, may be witnessed
in the vicinity of any radiator in a steam-heated building, while
the hot-air furnace installed in many homes depends upon con-
vection currents. If currents can be established at such low
temperature heads in a room at ordinary living temperature, it is
only logical that similar currents will be established where tem-
perature differences of several hundreds of degrees exist.
A phenomenon similar to the deflection of the current of heated
gases flowing through the broken baffle by cooler downward
currents can be observed by using an electric fan to break up and
distribute the current of hot air rising fronra radiator. The mere
fact that a certain amount of gas is being drawn off at one point
of the setting and a corresponding quantity of gas or air admitted
at another part will not affect the local convection currents any
more than the drawing off and admission of air into a room affects
the current of cold air at the windows and of the heated air at the
radiators.
Unfortunately we have all been hypontized by the idea that
any current of gas passing through a series of enclosures sweeps
uniformly through the full cross-section of all the passages or