RATIONAL CONSTRUCTION OF FURNACES
some of the useless and erroneous forms of boiler setting and
baffling which are given as " good " construction in Hutte are
shown below. These will very clearly indicate the ideas which
the author is endeavoring to set forth.
Fig. 77 shows a single-drum cylindrical boiler as illustrated
upon page 865 of the first volume of the French translation of
Hutte (edition of 1911).
Fig. 78 shows the correct method of setting the same boiler.
All of the baffling which was supposed to force the hot gases to
travel in a zigzag path has been eliminated. The hot gases, being
light, have a tendency to rise and apply themselves to the shell
of the boiler. Any constrictions of their path have a detrimental
effect, as they tend to increase the velocity of flow. In order to
increase the time during which the heated gases remain in contact
with the boiler after leaving the firebox, the waste gas outlet has
been dropped as far as possible by lowering the hearth of the gas
chamber behind the bridge wall.
(Note by English translator.—This setting would be greatly improved by
placing the grate and firebox in a separate setting where the mixing gases
would not be chilled below the ignition point.)
The circulation of the gases in a boiler set in this way is effected
in the following manner: The boiler will be constantly bathed
by the hottest gases which tend to rise to the highest part of the
setting. As these gases are cooled they will drop lower and lower
by reason of their increase in weight while cooling. They will
finally, at their lowest temperature, fall to and pass out through
the waste gas outlet.
In order to avoid detrimental eddy currents it is necessary to