76 COMBUSTION AND FUELS 



whose length and diameter are known, calculate the mean 

 velocity of efflux by using the formula 



24.51Q 

 V m = -- -; (5) 



d 2 



find the value of / from the table, corresponding to this value 

 of V m , and substitute these values of / and V m in the formula 

 for the head. 



EXAMPLE. A 4-in. pipe, 2,000 ft. long, is to discharge 24,000 

 gal. of water per hr.; what head is necessary? 



24,000 24.51X61 



SOLUTION. Q = - = 6 j gal. per sec. V 



= 10.2 ft. per sec. From the table, /=.0205 for V m = S, and 

 .0193 for Vm = 12; assume that /= .02 for V m = 10.2. Then 



ft. 



COMBUSTION AND FUELS 



COMBUSTION 



Nature of Combustion. Combustion is the very rapid 

 chemical combination of two or more elements, accompanied 

 by the production of light and heat. The atoms of some of 

 the elements have a very great affinity or attraction for those 

 of other elements, and when they combine they rush together 

 with such rapidity and force that heat and light are produced. 

 Oxygen, for example, has a great attraction for nearly all the 

 other elements. For carbon, oxygen has a particular liking, 

 and whenever these two elements come into contact at a 

 sufficiently high temperature, they combine with great rapidity. 

 The combustion of coal in the furnace of a boiler is of this 

 nature. The temperature of the furnace is raised by kindling 

 the fire, and then the carbon of the coal begins to combine 

 with oxygen taken from the air. 



Products of Combustion. When carbon and oxygen com- 

 bine they form CO*, or carbon dioxide; when hydrogen and 



