Question

An axial turbine stage has a degree of reaction of \(50\%\) and operates with symmetrical velocity triangles (i.e., absolute inlet and exit flow angles are equal in magnitude but opposite in direction). The axial velocity remains constant through the stage. Which of the following statements is correct?

• A. The entire pressure drop occurs in the stator only
• B. The enthalpy drop in rotor equals the enthalpy drop in stator
• C. The whirl component of velocity at rotor exit is zero
• D. The stage work output is zero

Hint:

For a Parsons reaction turbine, \[ \boxed{ R=0.5 } \] which implies \[ \boxed{ \Delta h_{\text{rotor}} = \Delta h_{\text{stator}}. } \] The velocity triangles are symmetrical.

Answer 1

The Correct Option is B

Step 1: Recall the meaning of degree of reaction. The degree of reaction of a turbine stage is \[ \boxed{ R = \frac{\text{Rotor enthalpy drop}} {\text{Total stage enthalpy drop}}. } \]

Step 2: Use the given value of reaction. Given, \[ R=0.5. \] Hence, \[ \frac{\Delta h_{\text{rotor}}} {\Delta h_{\text{stage}}} = \frac12. \] Therefore, \[ \boxed{ \Delta h_{\text{rotor}} = \Delta h_{\text{stator}}. } \] Thus, the rotor and stator contribute equally to the total enthalpy drop. Hence, \[ \boxed{\text{The enthalpy drop in rotor equals the enthalpy drop in stator}.} \] Therefore, \[ \boxed{(B)} \] is the correct answer.