A 'Francis turbine' operates under:
Choose the correct answer
Low head < 5 m only
Medium to high head (45–600 m) with mixed-flow radial-to-axial direction — most common large turbine in India
High head > 600 m (Pelton head range)
Pumping only, not power generation
Correct Answer
B. Medium to high head (45–600 m) with mixed-flow radial-to-axial direction — most common large turbine in India
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Francis turbine (mixed-flow reaction turbine): water enters radially through spiral casing and guide vanes, exits axially. Head range: 45–600 m (medium-high). Specific speed Ns = 60–300 rpm. Fixed runner blades. Most widely used for medium/large hydropower (most Indian dams: Bhakra, Tehri use Francis). Runner: S-runner, pump-turbine. High efficiency at design point (> 90%) but drops off at part load.
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