A Pelton wheel operates under a head of 40 m and develops shaft power of 800 kW which runs at 500 rpm. Assume the overall efficiency of the Pelton turbine as 80%. Find the flow rate of water. [Density of water = 1000 kg/m3, Acceleration due to gravity = 10 m/s2]

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NHPC JE Mechanical 6 April 2022 (Shift 1) Official Paper
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  1. 2.0 m3/s
  2. 2.5 m3/s
  3. 1.5 m3/s
  4. 3.0 m3/s

Answer (Detailed Solution Below)

Option 2 : 2.5 m3/s
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Detailed Solution

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Concept:

The overall efficiency of the Pelton wheel is given by,

\({η _o} = \frac{{Shaft \;Power}}{{Water\; Power}}\)

Water Power = ρQgH 

Calculation:

Given:

Shaft Power = 800 kW, ηo = 0.8, H = 40 m

ρ = 1000 kg/m3, g =10 m/s2

\({η _o} = \frac{{Shaft \;Power}}{{Water\; Power}}\)

\({0.8} = \frac{{800}}{{Water\; Power}}\)

Water Power = 1000 kW

Water Power = ρQgH 

1000 × 103 = 1000 × Q × 10 × 40

Q = 2.5 m3/s.

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