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Full text of "The Flow Of Gases In Furnaces"

140

RATIONAL CONSTRUCTION OF FURNACES

of chilled gas (water) which forms in those continuous heating
furnaces having an ascending roof and hearth. It is readily seen
that in this last case the forcing out of the cold gases by the hot
gases flowing into the heating chamber is obstructed to the highest
degree.

The performance of these furnaces, when constructed with a
horizontal hearth, is slightly better. This type of hearth does not
form a pocket for the cold gases, but the flow of the colder gases
to the waste-gas port is very nearly cut off by the ingots which
are being heated.

In computing the width of the hearth of the furnace it is necessary
to give thorough consideration to the fact that the cold gases must
be removed from the heating chamber. In practice the hearth is
sometimes given a width equal to twice the length of the ingot to

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FIG. 118.
be heated, so that at each end of the ingots a wide channel will be
formed for the cold gases.
What reason can be assigned for making the hearth so wide?
Would it not be better to proportion the width of the furnace
more closely to the length of the ingots or billets to be heated?
The author has been unable to find any other reply to the fore-
going questions than the following: In order that the furnace may
operate well and heat uniformly, it is absolutely necessaiy that
the burned gases be rapidly and completely carried away from the
heating chamber. The side channels, at the two ends of the file
or tier of ingots which are being reheated, form the only path by
which these gases may pass from the furnace. If a low temperature
at the charging end of the furnace is desired, it is necessary that
these channels" should have sufficient width.
In the case shown (Fig. 118), the continuous furnace has the
roof and hearth horizontal, and the height of the gas port above
the bridge wall is h; the height of the working doors is less than
this dimension; the waste gases are carried away from the heating