474 



HYDKAULICS AND ITS APPLICATIONS 



while the energy rejected in the discharge 



From this we have : 



Energy lost inside the wheel by hydraulic friction, etc. 

 = Energy given to wheel, Energy accounted for per second 



= QW\II- (V - W) * _(*-) ul = E F . 



L 2 g g J 



Energy lost per second in overcoming friction of bearings 



= E = 



y 



The distribution of energy may be shown graphically as in Fig. 216, 

 which records the results of a series of trials by the author on such a 

 wheel. The details of the wheel were as follows : 



Diameter of nozzles '253 inches. 



Number of nozzles . . . . .2. 

 Radius of nozzle path ..... 5 '875 inches. 

 Head of water above nozzles .... 3*20 feet. 

 In these trials the power was absorbed by means of a Prony brake 



applied to a horizontal drum. Water is ad- 

 mitted by means of a vertical down pipe P 

 (Fig. 215) open at the bottom, and con- 

 centric with the rotating tube T, and trouble 

 caused by the entrainment of air bubbles in 

 the down-coming stream is thus avoided. 

 The maximum brake efficiency of this ma- 

 chine, as determined from the results of a 

 large number of tests is 60' 6 per cent. 



The maximum efficiency was obtained 

 with a speed of 295 revolutions per minute, giving a nozzle velocity oi 

 14-75 f.s. 

 In this case, for maximum efficiency u = 1*49 V g h 



= 1-052 VaT/L 



FIG. 217. 



From this we have 



V 



1 + - 1 = 1-49 2 = 2'22. 



F 



F = 



9-38 



= '1065. 



. Substituting these values in the expression for the theoretical hydraulic 

 efficiency we get ?; = 69'2 per cent., as against the value, 64 per cent., 

 actually obtained. 



