Question:-
For a reaction turbine with degree of reaction equal to 50%, (V is the absolute steam velocity at inlet and a is the angle made by it to the tangent on the wheel) the efficiency is maximum what the blade speed is equal to
Option (A)
V cosa/2
Option (B)
2V cosa
Option(C)
V cos2a
Option(D)
V cosa
Correct Option:
(D)
Question Solution:
Efficiency (h) = {2r(2 cos a - r) / (1-r2 + 2r cos a)}
dh/dr = 0; i.e. - 2r - 2cos a = 0
r = cosa
hmax = {2cos2a / (1+cos2a)}
question-answer-faq-9616