STEAM BOILERS 111 



Let H = height of chimney, in feet; 

 H. P. = horsepower of boiler or boilers; 



A = actual area of chimney, in square feet; 

 = effective area of chimney, in square feet; 

 5 =side of square chimney, in inches; 

 d = diameter of round chimney, in inches. 



o rr r> 



Then, E=^p = A-.6VZ (1) 



H. P. = 3.33E Vff (2) 



S=12V+4 (3) 



d =13.54 Vfi+4 (4) 



The accompanying table has been computed from these 

 formulas. 



EXAMPLE 1. What should be the diameter of a chimney 

 100 ft. high that furnishes draft for a 600-H. P. boiler ? 



.3X600 

 SOLUTION. Substituting in formula 1, E = = 18. 



VlOO 

 Now, using formula 4, d= 13.54 Vis +4 = 61.44 in. 



EXAMPLE 2. For what horsepower of boilers will a chimney 

 64 in. sq. and 125 ft. high furnish draft ? 



SOLUTION. By simply referring to the table, the horsepower 

 is found to be 934. 



Maximum Combustion Rate. The maximum rates of com- 

 bustion attainable under natural draft are given by the 

 following formulas, which have been deduced from the 

 experiments of Isherwood: 



Let F = weight, in pounds of coal per hour per square foot 



of grate area; 



H = height, in feet, of chimney or stack. 

 Then, for anthracite burned under the most favorable con- 

 ditions, 



F = 2\//-l (1) 



and under ordinary conditions, 



F=1.5V//-1 (2) 



For best semianthracite and bituminous coals, 



F = 2.25V'// (3) 



and for less valuable soft coals, 



F = 3\// (4) 



