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Full text of "The Flow Of Gases In Furnaces"

22

APPLICATION OF THE LAWS OF HYDRAULICS

the furnace is in equilibrium with the atmospheric pressure may be
changed to about the mid-height of the working door. This will
produce the following results: the pressure at the level of the
hearth of the furnace will be reduced below that of the atmosphere
and will be ( 0 mm 36), and air from outside the furnace will
commence to flow into it under the door; the pressure at the top
of the door will be diminished by one-half, becoming (+0 mm 36),
and the loss of hot gases will be diminished correspondingly.

2.  Hydrostatic pressure readily explains the irregular working
of sloping grates in gas producers fired with wood.    There is a
current of gas with such a grate, as indicated by the arrow at the

right of Fig. 17. The
negative pressure which
exists at the level of
the horizontal grate
bars varies gradually
until it becomes posi-
tive at the top of the
sloping grate (compare
with page 141), under
which some of the gas
commences to escape
and burn, a pure loss of
energy. C1) The decrease
in the draft produced in

this manner also occurs with the sloping grates used under boilers.

This is the reason why

this type of   grate has

never   been   considered

satisfactory with natural

draft.

3.  The  existence   of
this hydrostatic pressure
readily explains the draft
of gas  producers which
operate without forced
draft, with the Siemens

siphon (Fig. 18).   The gas from the producer passes up through

(1) With forced draft and a closed ash pit, sloping grates work compara-
tively well.

17.

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