Fluid Mechanics

11.A bed consists of particles of density 2000 kg/m3. If the height of the bed is 1.5 metres and its porosity 0.6, the pressure drop required to fluidise the bed by air is

  1. 25.61 kPa
  2. 11.77 kPa
  3. 14.86 kPa
  4. 21.13 kPa
Correct answer: (B)
11.77 kPa

12.A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle system (in SI units) is given below:
Δ P/L = 375 × 103 VOM + 10.94 × 106 v2 OM (SI units)
If water is to be used as the fluidising medium, in actual operation, the above bed has a height = 1 m. What is the porosity of the fluidised bed?

  1. 0.2
  2. 0.5
  3. 0.7
  4. 0.8
Correct answer: (C)
0.7

13.A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle system (in SI units) is given below : Δ P/L = 375 × 103 VOM + 10.94 × 106 v2 OM (SI units) If water is to be used as the fluidising medium, the minimum fluidisation velocity, VOM is

  1. 12 mm/s
  2. 16 mm/s
  3. 24 mm/s
  4. 28 mm/s
Correct answer: (B)
16 mm/s

14.A Bingham fluid of viscosity μ = 10 Pa.s and yield stress, η0 = 10 KPa, is shared between flat parallel plates separated by a distance of 10-3 m. The top plate is moving with a velocity of 1 m/s. The shear stress on the plate is

  1. 10 KPa
  2. 20 KPa
  3. 30 KPa
  4. 40 KPa
Correct answer: (B)
20 KPa

15.A centrifugal pump designed to pump water is employed to pump a more viscous oil. In the later case, the pump

  1. Develops a lower head
  2. Capacity is reduced
  3. Requires more power
  4. All (A), (B) and (C)
Correct answer: (D)
All (A), (B) and (C)

16.A centrifugal pump has the following specifications:
Power = 4 H.P.; Speed = 800 rpm
Head = 8 metres
Flow = 1000 litres/minutes.
If its speed is halved, the new discharge will be _________ litres/minute.

  1. 500
  2. 200
  3. 1000
  4. 750
Correct answer: (A)
500

17.A centrifugal pump has the following specifications:
Power = 4 H.P.; Speed = 800 rpm
Head = 8 metres
Flow = 1000 litres/minutes.
If its speed is halved, the power consumed now will be _________ hp.

  1. 0.5
  2. 2
  3. 4
  4. 1
Correct answer: (A)
0.5

18.A centrifugal pump has the following specifications:
Power = 4 H.P.; Speed = 800 rpm
Head = 8 metres
Flow = 1000 litres/minutes.
If its speed is halved, then the new head will be _________ metres.

  1. 2
  2. 4
  3. 8
  4. 5.5
Correct answer: (A)
2

19.A centrifugal pump is called a turbine pump, if it is having a

  1. Turbine type impeller
  2. Vaned diffusion casing
  3. Rotating vaned volute
  4. None of these
Correct answer: (B)
Vaned diffusion casing

20.A centrifugal pump loses prime after starting. The reason of this trouble may be

  1. Incomplete priming
  2. Too high a suction lift
  3. Low available NPSH and air leaks in the suction pipe
  4. All (A), (B), and (C)
Correct answer: (D)
All (A), (B), and (C)
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