In all reaction turbines, maximum efficiency is obtained if (Note: All angles are measured with respect to the direction of the peripheral velocity.)
- Athe guide vane angle is 90°
- Bthe blade angle of the runner is 90° at the inlet
- Cthe blade angle of the runner is 90° at the outlet
- Dthe angle of the absolute velocity vector at the outlet is 90°Correct
Solution
Concept
Condition for maximum efficiency
Step-by-step solution
1. Maximum efficiency needs no whirl at the outlet, i.e. the absolute velocity is axial/radial (90° to the peripheral velocity).
Explanation
Exit kinetic energy is minimised.
Why the other options are wrong
Other angles do not give zero whirl.
Shortcut
Vw2 = 0.
Correct answer: D) the angle of the absolute velocity vector at the outlet is 90°