Reaction turbines – where does the steam pressure drop occur? In a reaction steam turbine stage, the steam's static pressure is reduced in which blade rows?

Introduction / Context:Impulse and reaction turbines differ in how the pressure and velocity of steam change across stator and rotor passages. Correctly characterizing the distribution of pressure drop is fundamental to stage design and efficiency analysis.

Given Data / Assumptions:

• Single reaction stage with fixed (stator) and moving (rotor) blades.
• Steady flow, negligible leakage for conceptual understanding.
• Nozzle action may occur in both blade rows for a reaction stage.

Concept / Approach:In a reaction turbine, part of the enthalpy (pressure) drop occurs in the fixed blades and part in the moving blades. The moving blades act as expanding nozzles. In contrast, in a pure impulse stage the entire pressure drop occurs in the fixed nozzles, while the rotor ideally turns the jet without pressure change.

Step-by-Step Solution:Define reaction: R = (enthalpy drop in rotor) / (total stage enthalpy drop).If R > 0, there is pressure drop in the moving blades.Therefore, in a reaction stage, both stator and rotor experience pressure reductions.

Verification / Alternative check:Velocity triangles for reaction stages show acceleration in both blade rows, consistent with pressure decrease in each.

Why Other Options Are Wrong:

• (a) Describes an impulse stage.
• (b) Not physically consistent for a standard stage design.
• (d) and (e) contradict expansion physics.

Common Pitfalls:Equating all turbines with impulse behavior; many modern stages have finite reaction (e.g., 50% reaction in Parsons stages).

Final Answer:Pressure is reduced in both fixed blades and moving blades