k becomes one of
proportioning it to produce a certain available draft.

The loss in the stack due to friction of the gases can be calculated
from the following formula:

f W*W C H
[Delta]D = --------- (26)
A*A*A

in which

[Delta]D = draft loss in inches of water,
W = weight of gas in pounds passing per second,
C = perimeter of stack in feet,
H = height of stack in feet,
f = a constant with the following values at sea level:
.0015 for steel stacks, temperature of gases 600 degrees
Fahrenheit.
.0011 for steel stacks, temperature of gases 350 degrees
Fahrenheit.
.0020 for brick or brick-lined stacks, temperature of gases
600 degrees Fahrenheit.
.0015 for brick or brick-lined stacks, temperature of gases
350 degrees Fahrenheit.
A = Area of stack in square feet.

[Illustration: 24,420 Horse-power Installation of Babcock & Wilcox
Boilers and Superheaters, Equipped with Babcock & Wilcox Chain Grate
Stokers in the Quarry Street Station of the Commonwealth Edison Co.,
Chicago, Ill.]

This formula can also be used for calculating the frictional losses for
flues, in which case, C = the perimeter of the flue in feet, H = the
length of the flue in feet, the other values being the same as for
stacks.

The available draft is equal to the difference between the theoretical
draft from formula (25) and the loss from formula (26), hence:

f W*W C H
d^{1} = available draft = KH - --------- (27)
A*A*A

Table 53 gives the available draft in inches that a stack 100 feet high
will produce when serving different horse powers of boilers with the
methods of calculation for other heights.

TABLE 53

AVAILABLE DRAFT

CALCULATED FOR 100-FOOT STACK OF DIFFERENT DIAMETERS ASSUMING STACK
TEMPERATURE OF 500 DEGREES FAHRENHEIT AND 100 POUNDS OF GAS PER HORSE POWER

FOR OTHER HEIGHTS OF STACK MULTIPLY DRAFT BY HEIGHT / 100

+-----+-------------------------------------------------------------------+
|Horse| |
|Power| Diameter of Stack in Inches |
+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |3