Question

In an axial compressor, the change in angular momentum of air through the rotor is directly related to

• A. Pressure at the inlet
• B. Work done per unit mass on the air
• C. Degree of reaction
• D. Rotor efficiency

Hint:

Euler's turbine equation: \[ \boxed{ W=u(V_{w2}-V_{w1}) } \] shows that the work transfer is directly proportional to the change in angular momentum.

Answer 1

The Correct Option is B

Step 1: Recall Euler's turbomachinery equation. For an axial compressor, \[ \boxed{ W=u(V_{w2}-V_{w1}), } \] where
• \(W\) = work done per unit mass,
• \(u\) = blade speed,
• \(V_{w1},V_{w2}\) = whirl components of velocity.

Step 2: Relate work to angular momentum. The change in whirl velocity represents the change in angular momentum of the air. Hence, \[ \boxed{ \text{Change in angular momentum} \Longrightarrow \text{Work done on the air}. } \] Therefore, \[ \boxed{\text{Work done per unit mass on the air}} \] is the correct answer. Thus, \[ \boxed{(B)} \] is the correct answer.