464 Molesworth’s pocket-book
Evaporative Performance of Steam Boilers.
(D. K. Clark, ‘ Min. Inst. Civ. Eng.,’ vol. xlvi.)
w = lbs. of water evaporated per square foot of grate per
. hour.
c = lbs. of fuel consumed per square foot of grate per hour.
E = Efficiency of fuel = — .
c
h = Heating surface in square feet.
g =. Grate surface „
r = Ratio of heating to grate surface = - •
a — A constant varying with each boiler
= Coefficient of fuel consumed per square foot of grate.
A ±= Coefficient of water consumed a ri.
w = A + Bc ~ a ri + Be.
r-_ y/c ( K - B)
a a
v< — art ar9
B ~ E—B’
Minimum value ofc when r = Values of w for any Ratio, r. •0222I-2+ 9-56C •016 7-2 + 10-25C •008 r* + 8-6c • 009 ri + 9-7 c ■Olin ri + 7'94 c Limiting
Stationary .. Marine.. .. Portable.. .. Locomotive,) coal .. j Ditto, coke .. 30 6-8 6-3 1-8 2-9 4-0 12-1 11-2 3-2 5-2 7-0 50 18-9 17-5 5*0 8-1 11-0 75 18'3 25 Value of c. •00755 ri • 007 ri • 002 ri • 00325 ri • 0044 j-2
For lower than the limiting values ofc, the values of w are 12’5 c for coal and 12c for coke. In locomotives the limit is from 100 to 120 lbs. of coal or coke per square foot per hour. Experiments in France gave as the average of the Lan- cashire, the Elephant, and the Fail bairn “5-tube” boilers a~ "0113 and B = 1 • 82. ’