## Fluid Mechanics and Hydraulic Machinery Miscellaneous

#### Fluid Mechanics and Hydraulic Machinery

1. Which one of the following is NOT a rotating machine?

1. NA

##### Correct Option: C

NA

1. A pump handling a liquid raises its pressure from 1 bar to 30 bar. Take the density of the liquid as 990 kg/m3. The isentropic specific work done by the pump in kJ/kg is

1. Work done by pump = υ(p2 – p1)

 = (30 - 1) × 100 990

= 2.93 kJ/kg

##### Correct Option: D

Work done by pump = υ(p2 – p1)

 = (30 - 1) × 100 990

= 2.93 kJ/kg

1. Water flows through two different pipes A and B of the same circular cross-section but at different flow rates. The length of pipe A is 1.0 m and that of pipe B is 2.0 m. The flow in both the pipes is laminar and fully developed. If the frictional head loss across the length of the pipes is same, the ratio of volume flow rates QB /QA is _____ (round off to two decimal places)

1. NA

##### Correct Option: A

NA

1. Water (density = 1000 kg/m3) at ambient temperature flows through a horizontal pipe of uniform cross-section at the rate of 1 kg/s. If the pressure drop across the pipe is 100 kPa, the minimum power required to pump the water across the pipe, in Watt, is _______.

1. W = m v(P1 - P2)

 W = 1 × 1 100 × 103 = 10 Watt 1000

##### Correct Option: A

W = m v(P1 - P2)

 W = 1 × 1 100 × 103 = 10 Watt 1000

1. For steady, fully developed flow Inside straight pipe of diameter D, neglecting gravity effects, the pressure drop ∆p over a length L and the wall shear stress τW are related by

1. Shear stress on wall,

 τW = -δP . R δx 2

 where -δP . ∆ δx L

 & R = D 2

 ∴ τW = ∆P × D = ∆PD L 2 x 2 4L

##### Correct Option: A

Shear stress on wall,

 τW = -δP . R δx 2

 where -δP . ∆ δx L

 & R = D 2

 ∴ τW = ∆P × D = ∆PD L 2 x 2 4L