Stage count comparison For the same required power output and inlet/exhaust conditions, an impulse turbine generally requires how many rows/stages of blades compared with a reaction turbine?

Introduction / Context:
The number of stages in a steam turbine affects shaft speed, efficiency, cost, and length. Impulse and reaction staging distribute the same overall enthalpy drop differently between fixed and moving rows, which influences how many rows are required for a given duty.

Given Data / Assumptions:

• Comparable inlet pressure/temperature and exhaust pressure for both turbine types.
• Similar design limits on blade speed and stage loading.
• Target: same power output.

Concept / Approach:

Impulse stages take nearly all pressure drop in fixed nozzles and mostly turn jets in the rotor; each stage extracts a limited work per unit pressure ratio without excessive exit losses. Reaction stages share pressure drop between stator and rotor, typically achieving higher stage loading for similar flow conditions. Hence, to absorb the same total enthalpy drop, an impulse machine usually needs more stages (more blade rows) than a reaction machine.

Step-by-Step Solution:

Verification / Alternative check:

Practical turbine lineups show many impulse stages for high pressure ratios, while reaction machines can reach similar duties with fewer rows at comparable speeds, confirming the trend.

Why Other Options Are Wrong:

Less/equal: contradicts typical stage-loading capabilities.“Cannot be compared”: broad trends are well established in design texts.“Zero”: impulse turbines still require stages to extract work.

Common Pitfalls:

Ignoring mechanical limits on blade speed and length; single-stage impulse devices (De Laval) run at very high speeds and cannot absorb large drops alone in practical large-power applications.

Final Answer:

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