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Full text of "The Flow Of Gases In Furnaces"

METHODS OF COMPUTING FOR FURNACES             79
burned is assumed, according to the operating condition of the
furnaces to be designed.
3.  The theoretical calorific intensity of the combustible, with
the assumed excess air supply over that theoretically required, LS
computed. W
4.  The following temperatures have been established for the
gases leaving the heating chambers of furnaces:
Open-hearth furnaces.....................   1600°
Puddling and reverberatory furnaces.......   1250°
Tempering or heat treating furnaces........    850°
Annealing furnaces, etc...................   1000°
5.  The difference between the computed temperature, or the
theoretical calorific intensity, and the temperature of the gases
leaving the heating chamber is divided by the number of degrees
of temperature drop of the gases per second.    This determines the
length of time during which the hot gases remain in the heating
chamber.
6.  Dividing the volume of the heating chamber by the time
during which the hot gases remain in it gives Qt, the volume of the
gas at the temperature £, which passes through the heating chamber
each second.    This value divided by 1+al, gives the volume of
the gases at 0°, and, according to the volume of gases required
at 0°, the quantity of fuel required per second, per hour or per
twenty-four hours will be fixed.
7.  Knowing Qh according to formulas previously given, the
principal dimensions of the furnace may be determined.    This is
done by fixing the velocity of flow of the gases in the different
parts of the furnace, and then computing, according to the condi-
tions, the hydrostatic pressure of the gases and the vertical dis-
^Note by translator.—This maybe done by the use of the methods of Mallard
and Le Chatelier. The theoretical calorific intensity, however, assumes that
combustion occurs instantaneously in an athermal chamber, the total amount
ot heat released being absorbed in increasing the temperature of the products
of combustion. In practice the velocity of combustion is not instantaneous
but requires an appreciable time interval; the chamber in which combustion
occurs is more or less dithermal and for this reason the practical or actually
obtained calorific intensity is less than the theoretical. A further difference
is due to the fact that the fuel usually contains more or less moisture, gases
being frequently saturated to the dew-point temperature, and in addition the
air supply contains some moisture. The design and construction of the
furnace affect the result.