Hydraulic Turbines and Jets MCQ

81. A hydraulic turbine has a discharge of 5 m3/s, when operating under a head of 20 m with a speed of 500 rpm. If it is to operate under a head of 15 m, for the same discharge, the rotational speed in rpm will approximately be

  1. 334
  2. 433
  3. 434
  4. 243
Answer
Answer. b

82. If Thoma’s cavitation factor is less than the critical factor, then the overall efficiency of a reaction turbine will have

  1. abnormal increase
  2. no change
  3. gradual increase
  4. sharp fall
Answer
Answer. d

83. A liquid jet of 30 m/s velocity is striking a single symmetrical moving curved vane at the centre. For maximum efficiency, the velocity of the vane should be

  1. 30 m/s
  2. 20 m/s
  3. 15 m/s
  4. 10 m/s
Answer
Answer. d

84. An unsymmetrical sprinkler has frictionless and equal flow through each of the two nozzles. If the absolute velocities are 6.0 m/s and 9.0 m/s, the ratio of the distances of the nozzles from the rotating shaft

  1. 91/2 : 61/2
  2. 9 : 6
  3. 92 :62
  4. 93 : 63
Answer
Answer. b

85. The speed of a geometrically similar turbine such that when it is developing 1 kW the total suction head is equal to 1 meter. The speed is known as

  1. unit speed
  2. specific speed
  3. suction specific speed
  4. critical speed
Answer
Answer. b

86. A fluid jet of cross sectional area of a and velocity of v strikes normal to moving plate arranged in series with velocity u and u < v, the actual fluid mass striking is equal to

  1. ρa(v – u)
  2. ρau
  3. ρa(v + u)
  4. ρav
Answer
Answer. a

87. A draft tube is fitted to the exit of a reaction turbine, located at 1.82 m above tail race level. The efficiency of draft tube is 75% and velocity of flow at the entry to draft tube is 10 m/s. The pressure at the entrance section of draft tube is

  1. -5 m
  2. -3.82 m
  3. 10.2 m
  4. 1.82 m
Answer
Answer. a

88. A reaction turbine discharges 35 m3/s under a head of 9 m and with an overall efficiency of 91%. The power developed in kW is

  1. 286.65
  2. 37.49
  3. 3.822
  4. 2866.5
Answer
Answer. d

89. If a certain oil of specific gravity 0.75 is conveyed through a pipe of 100 cm diameter, it encounters a nozzle of diameter 25 cm. By what % does the velocity of flow increase at the nozzle outlet w.r.t. the original velocity?

  1. 1200
  2. 1500
  3. 120
  4. 150
Answer
Answer. b

90. Flow number in turbines is defined as

  1. Q/ND
  2. Q/ND2
  3. Q/ND3
  4. Q/ND4
Answer
Answer. c
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