Hydraulic Turbines and Jets MCQ

91. If a multi-jet Pelton turbine has ‘n’ number of jets, then its specific speed is directly proportional to

1. n⁰
2. n^3/4
3. n^1/2
4. n

92. The cavitation in a hydraulic machine

1. causes noise and vibration of various parts
2. makes the surface rough
3. reduces the discharge of a turbine
4. causes sudden drop in power output and efficiency

93. The power developed by a turbine is

1. directly proportional to H^1/2
2. inversely proportional to H^1/2
3. directly proportional to H^3/2
4. inversely proportional to H^3/2

94. In an inward flow reaction turbine

1. the water flows parallel to the axis of the wheel
2. the water enters at the centre of the wheel and from there flows towards the outer periphery of the wheel
3. the water enters the wheel at outer periphery and then flows towards the centre of the wheel
4. the flow of water is partly radial and partly axial

95. If a turbine generates 10000 kW under the head of 10 m at the speed 100 rpm, the specific speed of the turbine is

1. 562.3 rpm
2. 177.8 rpm
3. 2056 rpm
4. 1052 rpm

96. If H is the unit head, the unit power of the turbine is proportional to

1. H^-2
2. H
3. H^-1/2
4. H^-3/2

97. A single jet impulse turbine of 10 MW capacity works with a head of 500 m. If the specific speed of the turbine is 10, the actual speed of the turbine is

1. 236.4 rpm
2. 106.9 rpm
3. 392.5 rpm
4. 50 rpm

98. If θ is the blade angle at the outlet, then the maximum hydraulic efficiency of an ideal impulse turbine is

1. (1 – cosθ)
2. (1 + cosθ)
3. (1 – cosθ)/2
4. (1 + cosθ)/2

99. A horizontal water jet with a velocity of 14 m/s and cross-sectional area of 10 mm² strikes a flat plate held normal to the flow direction. The density of water is 1000 kg/m³. The total force on the plate due to the jet would be

1. 1.96 N
2. Zero
3. 19.6 N
4. 0.196 N

100. The overall efficiency of a Pelton turbine is 70%. If the mechanical efficiency is 85%, What is its hydraulic efficiency?

1. 59.5%
2. 82.4%
3. 72.3%
4. 81.5%