The 'specific speed' Ns of a turbine is used to classify the type:
Choose the correct answer
Specific speed only determines blade material
Classifies turbine type: Pelton (low Ns, high head), Francis (medium), Kaplan (high Ns, low head)
Specific speed is only for pumps, not turbines
Higher Ns always means higher efficiency
Correct Answer
B. Classifies turbine type: Pelton (low Ns, high head), Francis (medium), Kaplan (high Ns, low head)
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Turbine specific speed Ns = N√P / H^(5/4) (with consistent units). OR Nq = N√Q / H^(3/4) (flow-based). Classification: (1) Pelton (impulse): Ns = 10–35 (high head 200–2000 m); (2) Francis (reaction, mixed flow): Ns = 50–300 (medium head 50–600 m); (3) Kaplan (axial flow): Ns = 300–900 (low head 5–70 m). High Ns → low head, high flow; Low Ns → high head, low flow. Specific speed: dimensionless parameter selecting turbine type.
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