DESIGN OF OPEN-HEARTH FURNACES
277
The gas and air necks, the cinder pockets and the uptakes are
next in order. The efficiency of the cinder pocket depends upon
the change in the direction of the flow, as well as upon the reduc-
tion in the velocity of flow. The width of the pockets fixes the
taper of the necks. Both pockets will be made the same width,
say, 2 m 00 (6.56 ft) with a space of 1 m 250 (4.10 ft) between
them. The gas neck will be 3 m 00 (9.84 ft) wide where it leaves
the chamber, tapering to 2 m 00 in a distance of about 3 m 750
(12.3 ft). The air neck will taper from a width of 5 m 00 (16.47 ft)
to 2 m 00 (6.56 ft) in the same distance. These figures have been
fixed arbitrarily and the assumption made that the same or
greater areas will exist than above the checkerwork.
Gas on
Gas
Air on Air
Gas on Waste Gas
Air on
Waste
Gas
Air and gas necks:
The frictional resistance will be
based on the following:
Z/= length of neck . .
3 m 750
4m 000
S= perimeter average. . . .
9 m 000
11 m 000
SL = surface ................
33.75
44.00
co = area in square meters
5m2 00
7m2 00
OJL/ ~f- CO = . . . . ....
6.75
6 28
Qt — volume of gases flowing . .
28m3 75
45m3 99
35m3 66
52m3 08
vt = Qt -:- co = m per sec
5m 75
6m 57
7m 13
7m 44
Aj = kg per m3 gas ..........
0.208
0.239
0.192
0.192
7= frictional resistance in kg per
0.016X6 75X5.75X0.208 =
0 kg 129
0 016X6 28X6 57X0 239 =
0 kg 144
0 016X6 75X6 57X0 192 =
0 kg 147
0 016X6 28X7 44X0 192 =
0 kg 144
The gas velocity in the necks is
slightly less than in the cham-
ber above the checkerwork
and is assumed the same as in
the cinder pockets. The pres-
sure in kilograms per m2 re-
quired to impress these veloci-
ties on the waste gases will be :
5=Aj(w/2-7-20) —kg per m2= . . .
0.354
0.525
0.495
0.543