Hydraulic Machines Questions and Answers – Significance of Specific Speed

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

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

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

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.

4. Impeller in a motor is used to _________
a) Change temperatures
b) Change Pressure
c) Kinetic energy change
d) Change density

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 _________

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.
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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

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 _______
b) Tail race distance
c) Tank dimensions
d) Turbine performance

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.

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

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

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.

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

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

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, ________
b) Tail race distance increases
c) Tank dimensions increases
d) Diameters of impeller increases

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

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

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.

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