The Flow Of Gases In Furnaces

56

APPLICATION OF THE LAWS OF HYDRAULICS

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bustion leaving the heating chamber, there is a temperature drop,
or cooling of the gases in the heating chamber, of 9()()°7 that is to
say, the gases remain in the* chamber only four or five seconds.

If these data are considered in connection with an ordinary type
of continuous heating furnace for ingots, in which the lower free
surface of the gases is in contact with the hearth of the furnace,
and the height from the hearth to the* roof is 0 m 75, the velocity
of the gases entering the heating chamber will be 5 m 41 per
second and of those leaving the chamber 3 m 42 per second.
The average velocity will be

5.41+3.42 , .t T

___^™_-==4 ni 41 por second;
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from this it may be determined that the length of such a furnace
will be from 17 m 00 to 22 m 50.

Therefore, when the velocity of the current of hot gases must
be limited to very small values the result will be a long heating
chamber.

One of the many defects in the olden* types of roverboratory
furnaces was the constriction of the opening over the bridge wall
where the hot gases entered the furnace. This resulted in an
impinging current of burning gases arid the rapid cutting away of
the brickwork owing to the high velocity of the gases. This high
velocity was considered necessary in order to effect an intimate
mixture of the combustibles and the eornburent. This method of
mixing is now considered undesirable4 and ineffective. In the
later types of reverberatory furnaces it has been completely
abandoned. An intimate mixture of the* producer gas from the
jfirebox and the secondary air is essential, but this mixture should
not be made at the bridge wall.

The height of the opening over the bridge wall may be com-
puted by Yesmann's formula

IX. REVERBERATORY FURNACES CONSIDERED AS INVERTED
WEIRS WITH A CISTERN OR .RESERVOIR. DIMENSIONS
UPON WHICH THEIR CORRECT OPERATION DEPENDS
As a general proposition, very long furnaces are not common
and in many cases are undesirable. Nevertheless, it is sometimes
necessary to retain the hot gases in the heating chamber as long