Fluid Mechanics and Hydraulic Machinery Miscellaneous
- For a Pelton wheel with a given water jet velocity, the maximum output power from the Pelton wheel is obtained when the ratio of the bucket speed to the water jet speed is ______ (correct to two decimal places).
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In pelton wheel:-
η= 2(vu -u2) v2
where,
u = bucket speed
v = water jet speed
So, For maximum efficiency:-dx = 0 du
2(v – 2u) = 0 v = 2uu = v 2 Correct Option: A
In pelton wheel:-
η= 2(vu -u2) v2
where,
u = bucket speed
v = water jet speed
So, For maximum efficiency:-dx = 0 du
2(v – 2u) = 0 v = 2uu = v 2
- Which one of the following statements is TRUE?
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Kaplan turbine is an axial-flow reaction turbine
Correct Option: D
Kaplan turbine is an axial-flow reaction turbine
- The blade and fluid velocities for an axial turbine are as shown in the figure.
The magnitude of absolute velocity at entry is 300 m/s at an angle of 65° to the axial direction, while the magnitude of the absolute velocity at exit is 150 m/s. The exit velocity vector has a component in the downward direction. Given that the axial (horizontal) velocity is the same at entry and exit, the specific work (in kJ/kg) is___________ .
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Given: V1 = 300 m/sec
u =150 m/sec
Vf1 = Vf2
(α = 25°)
V2 = 150 m/sec
Specific work = [Vw1 + Vw2]. u
Vw1 = V1 cos 25°
Vw2 = 300 cos 25°
= 271.89 m/s
Vf1 = Vf2 = V1 sin 25
Vf2 = 300 sin 25
= 126.78 m/s
Vw2 = √Vf12 - Vf22
= √1502 - 126.782 = √6426.83
Vw2 = 80.16 m/s
Specific work = [Vw1 + Vw2]. u
= [271.89 + 80.76] × 150
= 52807.5 J/kg
= 52.81 kJ/kgCorrect Option: C
Given: V1 = 300 m/sec
u =150 m/sec
Vf1 = Vf2
(α = 25°)
V2 = 150 m/sec
Specific work = [Vw1 + Vw2]. u
Vw1 = V1 cos 25°
Vw2 = 300 cos 25°
= 271.89 m/s
Vf1 = Vf2 = V1 sin 25
Vf2 = 300 sin 25
= 126.78 m/s
Vw2 = √Vf12 - Vf22
= √1502 - 126.782 = √6426.83
Vw2 = 80.16 m/s
Specific work = [Vw1 + Vw2]. u
= [271.89 + 80.76] × 150
= 52807.5 J/kg
= 52.81 kJ/kg
- Consider two hydraulic turbines having identical specific speed and effective head at the inlet. If the speed ratio (N1 /N2) of the two turbines is 2, then the respective power ratio (P1 /P2) is ____.
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Ns N√P H5/4
Given Ns1 = Ns2, H1 H2N1 = 2, P1 = ? N2 P2
N1 √P1 = N2√P2⇒ P1 = N1 2 P2 N2 = 1 2 = 0.25 2 Correct Option: C
Ns N√P H5/4
Given Ns1 = Ns2, H1 H2N1 = 2, P1 = ? N2 P2
N1 √P1 = N2√P2⇒ P1 = N1 2 P2 N2 = 1 2 = 0.25 2
- Which of the following statements are TRUE, when the cavitation parameter σ = 0?
i. the local pressure is reduced to vapor pressure
ii. cavitation starts
iii. boiling of liquid starts
iv. cavitation stops
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σ = 0 implies (i), (ii) and (iii)
Correct Option: D
σ = 0 implies (i), (ii) and (iii)