The Flow Of Gases In Furnaces

APPENDIX VII

Gas on Gas
Air on Air
Gas on Waste Gas
Air on Waste Gas

Draft depression in kg per m2 or mm of water B>t reversing valves . ....

27.983
23.516

7= fractional resistance in flue from valve, kg per rn2 .............

0.684
0.320

•S— velocity pressure in flue from valves, kg per m2 ......................

0.760
0.730

Total draft depression required at point of junction of flues .............

29.427
24.566

y = f rictional resistance in flue to stack or boiler in kg per m2 or mm of water . .

0.676

5 = velocity pressure required for stack flue — 2 250 — 0 730— kg perm2 . .

1 520

Total draft depression at base of stack or inlet to boiler kg per m2 or mm of water

31 623

In the foregoing, Mojarow's value for the coefficient of friction
(m = 0.016) was used. This coefficient was derived from observa-
tions made on Massick and Crook and Cowper hot-blast stoves.
.It is probably correct where a considerable portion of the flue
system consists of checkerwork. Murge, however, has deter-
mined the coefficients of friction of air at low temperatures in
mine galleries. The work was done very carefully. The coefficient
is one-third of that obtained by Mojarow, and is probably a closer
approximation when the flues are large and open. A further
confirmation of the fact that Mojarow's value is too high lies in
the fact that, in several cases where furnaces in service have
been analyzed, the computations showed the necessity for forced
draft. These furnaces were in operation without forced draft,
but in a more or less defective manner, giving operating troubles
and having a shorter campaign than normal. Applying Murge's
value for the coefficient of friction, the friction losses are reduced,
as is also the total draft depression required. The revised values
follow: