This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Effects and Precautions”.
1. The formation of vapour cavities is called _____
a) Static pressure drop
b) Cavitation
c) Isentropic expansion
d) Emulsion
View Answer
Explanation: The formation of vapour cavities is called cavitation. It is formed due to the presence of small free liquids with different zones. These zones consists of different layers of forces acting on them.
2. What is the degree of reaction denoted as?
a) D
b) R
c) r
d) d
View Answer
Explanation: Degree of reaction is defined as the ratio of the static pressure drop in the rotor to the static pressure drop in the stage. It can also be defined in the same way for enthalpy in different stages. It is denoted by the letter ‘R’.
3. Voids are created due to ______
a) Reaction ratio
b) Pressure ratio
c) Liquid free layers
d) Volumetric layers
View Answer
Explanation: Voids in a turbine or pump is created due to the presence of liquid free layers. It is formed due to the presence of small free liquids with different zones. These zones consists of different layers of forces acting on them.
4. Cavitation usually occurs due to the changes in ________
a) Pressure
b) Temperature
c) Volume
d) Heat
View Answer
Explanation: Cavitation usually occurs due to the changes in pressure. The pressure change is so rapid that it leads to formation of liquid free layers or cavities that start to affect the overall performance.
5. Degree of reactions are most commonly used in ________
a) Turbomachinery
b) Pressure drag
c) Aerodynamics
d) Automobiles
View Answer
Explanation: Degree of reaction is most commonly used in turbomachinery. Degree of reaction is defined as the ratio of the static pressure drop in the rotor to the static pressure drop in the stage. It can also be defined in the same way for enthalpy in different stages. It is denoted by the letter ‘R’.
6. At high pressure, the voids can generate ______
a) Drag force
b) Mass density
c) Shock waves
d) Flow speed
View Answer
Explanation: At high pressure, the voids can generate shock waves. Cavitation usually occurs due to the changes in pressure. The pressure change is so rapid that it leads to formation of liquid free layers or cavities that start to affect the overall performance.
7. Voids that implode near metal surface develops a_______
a) Drag force
b) Cyclic stress
c) Shock waves
d) Flow speed
View Answer
Explanation: Voids that implode near metal surface develops a cyclic stress. This happens mainly due to repeated implosion of voids.
8. Internal cavitation occurs due to __________
a) Drag force
b) Cyclic stress
c) Shock waves
d) Flow speed
View Answer
Explanation: At high pressure, the voids can generate shock waves. Cavitation usually occurs due to the changes in pressure. The pressure change is so rapid that it leads to formation of liquid free layers or cavities that start to affect the overall performance.
9. Non- inertial cavitation is the one in which a bubble of fluid is forced to oscillate.
a) True
b) False
View Answer
Explanation: Non- inertial cavitation is the one in which a bubble of fluid is forced to oscillate. It oscillates in a different size or shape due to some form of energy called the acoustic field.
10. The efficiency of the vane is given by _________
a) 1-V22/ V12
b) 1-(V22/ V12)
c) V22/ V12
d) 1- V12
View Answer
Explanation: In a velocity triangle at the inlet and the outlet, the control volume is moving with a uniform velocity. Therefore, the momentum theorem of the control volume is at a steady flow. Thus, the efficiency of the vane is given by 1-(V22/ V12).
11. The velocities of the blade angles can be found out using ________
a) Mach number
b) Froude’s number
c) Velocity triangles
d) Reynolds number
View Answer
Explanation: The velocity triangle represents various components. It mainly determines the velocities of fluids that act in a turbomachinery. It can be drawn for both inlet and outlet triangles with its angles.
12. Which among the following velocities cannot be found using the velocity triangle?
a) Tangential
b) Whirl
c) Relative
d) Parabolic
View Answer
Explanation: The velocity triangle represents various components. It mainly determines the velocities of fluids that act in a turbomachinery. It can be drawn for both inlet and outlet triangles with its angles.
13. Hydrodynamic cavitation is due to the process of _________
a) Vaporisation
b) Sedimentation
c) Filtration
d) Excavation
View Answer
Explanation: Hydrodynamic cavitation is due to the process of vaporisation. A bubble generation takes place in which implosion occurs during the flowing of liquid.
14. The process of bubble generation leads to __________
a) High temperatures
b) High pressures
c) High energy densities
d) High volumetric ratio
View Answer
Explanation: The process of bubble generation leads to high energy densities. The local temperatures and local pressures at this point last for a very short time.
15. Super cavitation is the use of cavitation effect to create a bubble of steam inside a liquid.
a) True
b) False
View Answer
Explanation: Yes, it is true. Super cavitation is the use of cavitation effect to create a bubble of steam inside a liquid. It is large to encompass an object passing through the liquid to reduce skin friction drag.
Sanfoundry Global Education & Learning Series – Hydraulic Machines.
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