Hydraulic Machines Questions and Answers – Degree of Reaction

This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Degree of Reaction”.

1. The formation of vapour cavities is called _____
a) Static pressure drop
b) Cavitation
c) Isentropic expansion
d) Emulsion
View Answer

Answer: b
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

Answer: b
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

Answer: c
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.
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4. Cavitation usually occurs due to the changes in ________
a) Pressure
b) Temperature
c) Volume
d) Heat
View Answer

Answer: a
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

Answer: a
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

Answer: c
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

Answer: b
Explanation: Voids that implode near metal surface develops a cyclic stress. This happens mainly due to repeated implosion of voids. Thus, option ‘b’ is correct.
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8. In case of gas turbines and compressors, degree of reaction is ________
a) Static pressure drop in rotor/ static pressure drop in stage
b) Static pressure drop in stage/ static pressure drop in rotor
c) Isentropic enthalpy drop in rotor/ isentropic enthalpy drop in stage
d) Static temperature drop in stage/ static temperature drop in rotor
View Answer

Answer: c
Explanation: Degree of reaction in terms of gas turbines and compressors is defined as the ratio of isentropic enthalpic drop that is developed in the rotor such as the moving blades to that of the isentropic heat drop in the fixed blades.

9. Non- inertial cavitation is the one in which a bubble of fluid is forced to oscillate.
a) True
b) False
View Answer

Answer: a
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.
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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

Answer: a
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

Answer: c
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

Answer: d
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

Answer: a
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

Answer: c
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. Thus, the option is ‘c’.

15. Super cavitation is the use of cavitation effect to create a bubble of steam inside a liquid.
a) True
b) False
View Answer

Answer: a
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.

16. Degree of reaction turbine is the ratio of?
a) Pressure energy to total energy
b) Kinetic energy to total energy
c) Potential energy to total energy
d) Kinetic energy to potential energy
View Answer

Answer: a
Explanation: Degree of reaction is defined to be the ratio of pressure and total energies inside the runner of a turbine.

17. Which of these options are best suited for the total energy change inside the runner per unit weight?
a) Degree of action
b) Degree of reaction
c) Turbulence
d) Efficiency of turbine
View Answer

Answer: b
Explanation: Degree of reaction is defined to be the ratio of pressure and total energies inside the runner of a turbine.

18. Which of these ratios are termed to be hydraulic efficiency?
a) Water power to delivered power
b) Delivered power to input power
c) Power lost to power delivered
d) Runner power to water power
View Answer

Answer: d
Explanation: From the equation of hydrodynamic machines, we get hydraulic efficiency to be the ratio of runner power and water power.

19. When a container containing a liquid is rotated, then due to centrifugal action, then which of these energies are changed?
a) Kinetic energy
b) Pressure energy
c) Potential energy
d) Energy due to viscous force
View Answer

Answer: b
Explanation: When a container containing a liquid is rotated, then due to centrifugal action there is a change in pressure energy.

20. For an actual reaction turbine, what should be the angle beta, such that the loss of kinetic energy at the outlet is to be minimum?
a) 90
b) 45
c) 60
d) 30
View Answer

Answer: a
Explanation: Only when the angle beta is 90, V2 will be minimum so that loss of kinetic energy is minimized.

21. Discharge through a reaction flow reaction turbine is given by, Q = ______
a) Pi*d*b*Vf1
b) Pi*d*d*b*Vf1
c) Pi*d*b*b*Vf2
d) Pi*b*b*Vf1
View Answer

Answer: a
Explanation: The discharge in a radial flow reaction turbine is the product of diameter, width and velocity of flow at inlet Vf1 with pi.

22. When the thicknesses of vanes are to be considered in the discharge of a turbine, what will be the area under consideration?
a) Pi*d – n*t
b) Pi*d – n*n*t
c) Pi*d – t*t
d) Pi*d *d– n*t
View Answer

Answer: a
Explanation: When the thicknesses of vanes are to be considered in the discharge of a turbine, and n is the number of vanes, are is given by Pi*d – n*t.

23. The speed ratio is defined as u/(2gH)1/2
a) True
b) False
View Answer

Answer: a
Explanation: The speed ratio is termed to be the ratio of tangential velocity at inlet to square root of 2gH.

24. Flow ratio is defined as Vf1/(2gH)1/2
a) False
b) True
View Answer

Answer: b
Explanation: Flow ratio is the ratio between velocities of flow at inlet to square root of 2gH. Here, H is the head of the turbine.

25. _________ means the angle made by absolute velocity with the tangent on the wheel is 90 degrees and the component of whirl velocity is zero.
a) Axial discharge
b) Tangential discharge
c) Turbulent discharge
d) Radial discharge
View Answer

Answer: d
Explanation: Radial discharge is the angle made by absolute velocity with the tangent on the wheel is 90 degrees and the component of whirl velocity is zero. Radial discharge at outlet means the angle beta is 90.

26. In a Francis turbine, degree of reaction lies between _____
a) 0 and 1
b) 1 and 2
c) 0 and 0.5
d) 0.5 and 0.1
View Answer

Answer: a
Explanation: For a Francis turbine, theoretically and practically, 0< R< 1.

Sanfoundry Global Education & Learning Series – Hydraulic Machines.

To practice all areas of Hydraulic Machines, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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