The Flow Of Gases In Furnaces

COMBUSTION AND BOILER SETTINGS

339

0 I 2

Distance from Central Position, Feet

FIG. 172.

Curve showing variation in temperature at points E and G at different distances from
the center line of the boiler shown in Fig. 170. Upper pair of curves shows the tempera-
tures indicated by moving twin couple E 1-in steps away from center line. Lower pair
of curves show indications of twin couple G when moved by 6-in steps away from the
center.

1300
1200
1100

1000

a

m

5'JO
400

\

2372
2192

2012

1832 3

1052 g
93* H

20 30

Time, Seconds

40

752

572

FIG. 173.—Curves Showing the Fluctuations of Temperature at Points A
and C in the Boiler Shown in Fig. 170.
The fluctuations were obtained by reading the small couple at two-second intervals.
These fluctuations are a beautiful illustration of the analogy between the flow of water and
the flow of hot gases. Couple C is located near the bottom of the steam drum where it is
immersed in a comparatively quiet body of gas. Couple A is located immediately below
the tubes at a point where it would show the effects of all the surges in the stream of flowing
gas. Anyone who has watched water flowing, from the top of a dam or the spout of a
pump, has noticed that the flow is broken up by numerous small surges. This pyrometer
shows the effect of the gas surges. Another factor contributing to these surges is the
refrigerating action of the water-cooled tubes on the gases. Chilled gases will be held
among the tubes in the same manner as a ball is supported by^a stream of water or air,
until the weight of chilled gases becomes sufficient to permit it to break its way down
through the up-flowing current of hot gases. Conditions similar .to this exist with all
the usual forms of boiler baffling, as they are well arranged to promote this condition.
One of the effects of this condition is the formation of soot and COz by the dissociation of
CO instead of its combustion. Considerable heat loss results.