THEORY OF TURBINE DESIGN 



583 



W Q 



The final moment of momentum = -- - w 3 r 3 ft. Ib. units. 



.-. Change of moment of mo- J = = WQ { _ , 



mentum = turning moment j // 



.-. Work done by this mo- ) IV Q < * n 



= - - 1 K'2 7- 2 w 3 r 3 } co ft. Ibs 

 ment per second j 



// 



IV ( ) 



= --- - 



Evidently this has its maximum value when w a = 0, and. then the 



ft. Ibs. 



work done per second = U = - { w 2 u 2 } ft. Ibs. 



i/ 



(1) 



the 



(2) 



FIG. 255. -Guide and Vane Angles for Inward Radial Flow Turbine. 



If tv 3 is not zero, we have, on substituting its value w 3 ~- w s / 3 cot > 

 W Q < 



TT 



U = 



9 



U' 2 ?/2 



u 3 f 3 cot y \ ft. Ibs. per second. 



If the vane angles are correctly proportioned as indicated in Fig. 255 

 so as to avoid shock afr entrance, we have : 



tan 



