Question:-
For maximum blade efficiency of a single-stage impulse turbine, the blade speed ratio, (a is the angle made by absolute velocity at inlet) should be
Option (A)
cos 2a
Option (B)
cos 2a / 2
Option(C)
cos a / 2
Option(D)
2 / cos a
Correct Option:
(C)
Question Solution:
For impulse turbine
hd = 2(rcoa- r2)(1+kc)
dhd/dr = 2(1+kc) (cosa - 2r)
For maximum efficiency
r = cos a / 2
(hd)max = cos2a
question-answer-faq-9602