The Flow Of Gases In Furnaces

APPLICATION OF THE LAWS OF HYDROSTATICS

19

draft, it becomes possible to take into account the manner in
which metallurgical furnaces operate.

The pressure of the gas within the laboratory of the furnace
is zero. The firebox acts to pump the elements necessary for the
formation of the flame into the furnace, and the chimney acts to
remove the products of combustion. This is the case with all
such furnaces and with all systems of heating, whether simple
coal-fired or using producer gas with or without the recuperation
of the heat. This rule is also applicable to coke ovens, to kilns
for the burning of brick or for the calcining of ores.

Each firebox acts as a force pump, functioning in the following
manner: assume that the firebox A (Fig. 15) is filled with gas at a
temperature of 1200°, that is to say, the specific weight of this

FIG. 15.
gas will be about one-fifth the weight of air. Under these condi-
tions each particle of air which is near the grate is acted upon,
on the side of the furnace, by the pressure of a column of gas h,
which is only one-fifth the weight of that which acts upon it on the
side exposed to the outside air. It is evident that a current
of air will be established by the action of this positive pressure,
which will be equal to the difference between the weight of a
column h of the outside or cold air and the same column of hot
gases.
The height of the column has been taken as h and not as 7iT,
because, in the furnace chamber, the current of hot gases rising
from the firebox must always be taken with regard to the hearth
level.
The positive pressure which is measured by the height of the
column h is expended: (a) in overcoming the resistance of the
bed of fuel to the passage of the air and the gas; (6) in creating