Hydraulic Machines Questions and Answers – Significance of Specific Speed

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This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Significance of Specific Speed”.

1. Specific speed is the speed of the turbine which is similar to its ________
a) Temperature difference
b) Pressure difference
c) Aspect ratio
d) Speed of rotor
View Answer

Answer: c
Explanation: Specific speed is the speed of the turbine which is similar to its aspect ratio. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.

2. Specific speeds are used in pumps to determine ________
a) Temperature
b) Reaction speed
c) Suction specific speed
d) Wheel speed
View Answer

Answer: c
Explanation: Specific speeds are used in pumps to determine. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.

3. Specific speed develops a unit power under a unit _______
a) Temperature
b) Pressure
c) Volume of the flow
d) Head
View Answer

Answer: d
Explanation: Specific speed develops a unit power under a unit head of the turbine. The unit head of the turbine plays an important role in denoting the specific speed of the turbine.
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4. Impeller in a motor is used to _________
a) Change temperatures
b) Change Pressure
c) Kinetic energy change
d) Change density
View Answer

Answer: b
Explanation: Impellers that are present in motors are used to increase or decrease the pressure of the fluid flow in the turbines. Thus, the correct option is ‘b’.

5. Hydraulic head is also called as _________
a) Pressure head
b) Density head
c) Kinetic head
d) Piezometric head
View Answer

Answer: d
Explanation: Hydraulic head is also called a Piezometric head. It is a measurement of the liquid pressure above the geodetic datum. Hydraulic head is usually measured as a liquid in surface elevation.

6. Specific speed of a Pelton wheel with single jet is _______
a) 8.5 to 30
b) 30 to 51
c) 51 to 225
d) 230 to 500
View Answer

Answer: a
Explanation: Specific speed of a Pelton wheel with a single jet is equal to 8.5 to 30. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.

7. Specific speed is an index used to predict _______
a) Head race distance
b) Tail race distance
c) Tank dimensions
d) Turbine performance
View Answer

Answer: d
Explanation: Specific speed of a turbine is used to predict its turbine performance. Specific speeds are used in pumps to determine. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery.
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8. Specific speed of a Pelton wheel with multiple jets is _______
a) 8.5 to 30
b) 30 to 51
c) 51 to 225
d) 230 to 500
View Answer

Answer: b
Explanation: Specific speed of a Pelton wheel with multiple jets is equal to 30 to 51. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.

9. Specific speed of a Francis turbine is _______
a) 8.5 to 30
b) 30 to 51
c) 51 to 225
d) 230 to 500
View Answer

Answer: c
Explanation: Specific speed of a Francis turbine is equal to 51 to 225. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.
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10. Specific speed of a Kaplan turbine is _______
a) 8.5 to 30
b) 30 to 51
c) 51 to 225
d) 355 to 860
View Answer

Answer: d
Explanation: Specific speed of a Kaplan turbine is equal to 51 to 225. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. Some of the main examples of turbomachinery are turbines. Specific speed plays an important role in the turbine.

11. Specific speed less than 500 are called _________
a) Positive displacement pumps
b) Negative displacement pumps
c) Draft tubes
d) Tanks
View Answer

Answer: a
Explanation: Specific speed less than 500 are called positive displacement pumps. Centrifugal pump impellers have speed ranging from 500- 10000 English units. IT has got radial flow with pumps mixed with axial flow pumps.

12. With the increase in specific speeds, ________
a) Head race distance increases
b) Tail race distance increases
c) Tank dimensions increases
d) Diameters of impeller increases
View Answer

Answer: d
Explanation: Specific speed of a turbine is used to predict its turbine performance. Specific speeds are used in pumps to determine. Specific speed is denoted by Ns. It is used to characterize speeds in turbo machinery. With the increase in specific speeds, diameter of the impellers increases.

13. Specific speed is used to predict desired pump or turbine performance.
a) True
b) False
View Answer

Answer: a
Explanation: Specific speed is used to predict desired pump or turbine performance. It predicts the general shape of the impeller. Thus, it is a true statement.

14. Once we know the desired functions of the specific speed, it is easier to calculate its components units.
a) True
b) False
View Answer

Answer: a
Explanation: Yes, Once we know the desired functions of the specific speed, it is easier to calculate its components units. Specific speed is used to predict desired pump or turbine performance. It predicts the general shape of the impeller.

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.

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Manish Bhojasia - Founder & CTO at Sanfoundry
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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