The Flow Of Gases In Furnaces

302 APPENDIX VIII

which would carry the gas to the dome in half a second. The
average time the gases remain in this chamber as computed from
their average temperature in the stove will be about five seconds.
The volume of gases formed each second in the combustion
chamber is

4.31X5.404 = 23 m3 29 with 40 per cent excess air,
4.75X5.404 = 25 m3 67 with 80 per cent excess air,

which would make the average area of the ascending column less
than 0 m2 70 or less than 20 per cent of the combustion chamber
area. The gas shoots across the short diameter of the chamber
and strikes the wall with considerable force. As a result of these
conditions, the flame in the combustion chamber may take on a
resonant vibration similar to that of the " singing flame " of the
physical laboratory.

The mushrooming of the burner jet is one of the causes for
the flame coming out around the burner. The hot column of
blazing gas will rise through the stagnant gases in the combustion
chamber and, since convection currents for gas are readily set up
there will be considerable recirculation. Noisy burning is a
well-known feature of stove operation. The mushrooming of the
gas jet assists in the mixing, and further mixing is effected when
the gases reach the dome. Mr. Maccoun's test proved that
unburned gases reached the dome but did not pass down into the
checkerwork.

The draft conditions existing in a stove are peculiar, inasmuch
as there may happen to be a greater draft depression at the
chimney valve than at the foot of the stack. This arises from the
fact that upward pressure exists in the combustion chamber and
likewise, to a lesser extent, in the checker, and these pressures
counterbalance each other. Assuming for the sake of simplicity
that the waste gases, etc., have the same specific weight as air,
the upward pressure in the combustion chamber will be

Ai2 oo = 23.101.29--- =+26.20 mm of water.
V 1+at/

In the checker this upward pressure will be
= 26.10/1.29

2X273