DESIGN OF OPEN-HEARTH FURNACES
283
Gas on Gas
Air on Air
Gas on Waste Gas
Air on
Waste Gas
7= friction loss between port and valves, revised, kg per m2 or mm of water. . . . d— pressure to impress velocities between port and valves, kg per m2 or mm of water ...
1.114 3 300
1.185 2 351
1.265 4 756
1.109 2 419
Valve resistance, 5= kg per m2 .....
4 201
2 317
6 216
4 781
Summation, kg per m2 or mm of water . . Chimney effect of checkerwork, etc., kg per m2 or mm of water . .
8.615 12 851
6.853 10 683
12.237 13 217
8.309 12 990
Chimney effect available for port velocity.
4 236
3 830
Draft depression required at reversing valve
25.454
21.299
Gas on
Waste Gas
Air on Waste Gas
Revised figure for draft depression required at reversing valve, kg per m2 or mm. of water ........ .......
25.454
21.299
7= re vised frictional resistance in flue from valve, kg per m2 or mm of water
0 228
0 107
5= velocity pressure required in flues from valves ..........
0.760
0.730
Revised total draft depression required at point of junction of flues kg per m.2 or mm of water
26 442
22 136
T= revised frictional resistance in flue to stack or boiler, kg per m2 or mrn of water .............
0 226
8= velocity pressure required in stack flue, kg per rn2 or rnm of water .......................................
1 . 520
Total draft depression required at base of stack or boiler inlet, kg per m2 or mrn of water .............
28 . 188
The port areas and velocities may now be fixed. In so doing, it
should be borne in mind that the waste gases must pass out
through the gas- and air-ports in proper proportions to supply the
required amount of preheat. This is very rarely accomplished
when chimney draft is depended upon, particularly when the gas