Correct Answer - Option 2 : angle of absolute velocity vector at the outlet is 90°
Explanation:
The maximum efficiency of a reaction turbine is given by:
\(\eta = \frac{{2{{\cos }^2}α }}{{1 + {{\cos }^2}α }}\)
So for the maximum efficiency α = 90°
where,
α = angle of the absolute velocity vector at the outlet.