Impulse turbine expansion location In an impulse steam turbine stage, where does the expansion (pressure and enthalpy drop) of the steam occur?

Introduction / Context:
Steam turbines are broadly categorized as impulse or reaction based on where the pressure drop occurs. Identifying the expansion location is essential for drawing velocity triangles, estimating losses, and choosing appropriate blading for a given duty.

Given Data / Assumptions:

• Single impulse stage: one row of fixed nozzles followed by a row of moving blades.
• Idealized impulse behavior: negligible pressure drop across moving blades.
• Steady flow with well-formed jets issued by the nozzles.

Concept / Approach:
In an impulse stage, the entire pressure (enthalpy) drop of the stage occurs in the nozzles, converting thermal energy into kinetic energy. The moving blades then redirect the high-speed jet, changing its momentum at nearly constant static pressure to extract shaft work. This is contrasted with reaction stages, where pressure drops occur in both fixed and moving blades.

Step-by-Step Solution:
Nozzles: pressure ↓, velocity ↑ (enthalpy converted to kinetic energy).Moving blades: pressure ≈ constant; jet is turned, momentum change produces rotor work.Therefore, in an impulse turbine, expansion is wholly in the nozzles.

Verification / Alternative check:
Static-pressure measurements across a classical De Laval or Curtis stage show major pressure drop across stators, negligible across rotors—consistent with impulse theory.

Why Other Options Are Wrong:
“Wholly in moving blades” describes neither impulse nor reaction correctly. “Partly in both” is reaction behavior. “None of these” ignores established definitions.

Common Pitfalls:
Assuming pressure must drop in the rotor to get work; impulse stages rely on momentum change at near-constant pressure in the rotor.

Final Answer:
Wholly in the nozzles (fixed blades)