THEORY OF TURBINE DESIGN 



547 



Also, since tan y = n tan a, this makes tan y = '300, giving y the 

 value 16 42'. 



.) 9 



The theoretical hydraulic efficiency 2 -I- tan 2 a n W e( l ual8 2-053 

 = 97'4 per cent. 



Applying Fliegner's correction, it appears that for maximum efficiency 

 at this speed of rotation /3 should be increased from 90 to a value (3 r 

 where 



ff - o o , 90 -16-7 '79(1-30-1) 



^ ~ 



_ Q 



'79 



= 90 + 14-7 - 9 

 = 95-7. 



As will be seen later, these results, however, need further correction 

 for the thickness of the vanes at their inlet and outlet edges. 



AKT. 143. SOURCES AND MAGNITUDE OF LOSSES IN THE PRESSURE 



TURBINE. 



So far the various losses in the turbine and its appendages have been 

 neglected, and while it is impossible to take these fully into account in a 



theoretical discussion, yet a 

 more detailed examination 

 will be of value as indicating 

 their relative importance. In 

 general, these losses consist 

 of: 



(1) Frictional losses in sup- 

 ply and discharge pipes. 



(2) Loss by leakage between 

 guides and wheel. 



(3) Losses due to shock at 

 FlG 258 entrance if the vane angles 



are not adapted to the speed 



of the wheel, and to contraction and subsequent expansion of section of 

 the stream. 



(4) Frictional losses due to motion of the water over the vanes and 

 crown of the wheel. 



(5) Eddy losses caused by any sudden curvature of the vanes by sudden 

 changes of section or divergence of the passages. 



(6) Losses due to shock caused by sudden enlargement of the stream 

 section on entering the buckets at part gate. 



N N 2 



