Discussion
Select the correct statement for 50% reaction stage in a steam turbine.
Answer: D
The correct statement is the absolute exit flow angle is equal to inlet angle of rotor blade.
In a 50% reaction (Parsons) stage the enthalpy drop is split equally between the fixed and moving blades, so the two rows are identical in shape and the velocity triangles at inlet and exit are mirror images. As a result, the absolute inlet angle equals the relative exit angle (α1 = β2), and the relative inlet angle, which is the rotor blade inlet angle, equals the absolute exit angle (β1 = α2).
Symmetric blades, with equal inlet and exit angles, are the mark of an impulse stage, so the options calling the rotor or stator blade symmetric are wrong. The absolute inlet and exit flow angles are not equal in general; it is the cross pairs that match.
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