Impulse turbine compounding – efficiency comparison Compared with a pressure-compounded impulse turbine (Rateau staging), the efficiency of a pressure-velocity compounded impulse turbine (Curtis staging) is generally:

Introduction / Context:
Impulse turbines may be compounded by pressure (multiple nozzle stages) or by velocity (multiple rows of moving blades with intermediate guide blades), or by a combination of both. Knowing how compounding affects efficiency guides stage selection.

Given Data / Assumptions:

• Equal overall pressure ratio and comparable design practice.
• Similar blade quality and leakage assumptions for comparison.
• Focus on aerodynamic/rotordynamic losses from additional blade rows.

Concept / Approach:
Pressure compounding spreads the pressure drop across several nozzle stages, generally keeping blade relative speeds moderate with fewer moving rows per stage. Pressure-velocity compounding introduces extra moving rows within a stage to split absolute jet velocity, but each added row brings turning, friction, and tip/leakage losses, typically lowering stage efficiency relative to pressure compounding.

Step-by-Step Solution:
Recognize that Curtis staging adds rows → more cumulative losses.Rateau staging uses more nozzle sets but fewer moving rows per stage → lower cumulative moving-blade losses.Therefore, for similar conditions, pressure-velocity compounded stages are generally less efficient than pressure-compounded ones.

Verification / Alternative check:
Textbook comparisons and test data show diagram efficiency penalties with additional blade rows due to repeated incidence, friction, and wake mixing.

Why Other Options Are Wrong:

• “More” contradicts typical loss accumulation behavior.
• “Same” ignores extra rows and losses.
• “Always 100%” is impossible in real turbines.
• “Indeterminate” is overly cautious for standard design principles.

Common Pitfalls:
Focusing solely on speed reduction benefits of Curtis staging while overlooking added loss sources.

Final Answer:
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