202 STEAM ENGINES 



As the condensed steam from the surface condenser is gen- 

 erally pumped back into the boiler as feedwater, it is desirable 

 to have it as hot as possible; but it must be remembered that 

 it is impossible to get the feedwater from the condenser at a 

 higher temperature than that of saturated steam at the abso- 

 lute pressure existing in the condenser. 



It will be considerably cooler than this if, after being con- 

 densed, it is allowed to lie in the bottom of the condenser 

 and give up its heat to the circulating water. The heat 

 thus given up is a total loss, and should be avoided by con- 

 necting the air-pump suction to the lowest point of the con- 

 denser and by shaping the bottom of the condenser so that the 

 water will drain rapidly into the air-pump suction. 



Cooling Water for Surface Condenser. The amount of 

 cooling water required in the case of a surface condenser may 

 be found by the formula 



H- (/-32) 



t-h ' 

 in which Q = number of pounds of cooling water required to 



condense 1 Ib. of steam; 

 H = total heat above 32 of 1 Ib. of steam at pressure 



at release; 

 < - temperature of condensed steam on leaving 



condenser; 



t\ = temperature of cooling water on entering con- 

 denser; 



*2 = temperature of cooling water on leaving condenser. 

 EXAMPLE. Steam exhausts into a surface condenser from 

 an engine cylinder at a pressure of fi Ib., absolute; the tempera- 

 ture of the condensing water on entering is 55 P., and on leaving 

 it is 100 F. ; the temperature of the condensed steam on leaving 

 the condenser is 125 F. How many pounds of cooling water 

 are required per pound of steam? 



SOLUTION. The total of 1 Ib. of steam at 6 Ib., absolute, 

 from the Steam Table, is 1,133.8 B. T. U. Then, substituting 

 the values of H, t, t\, and fj in the formula, 



l.i:..X-(125-32) 1.040.8 

 '-- ,,, " 45 



