# Thermodynamics Questions and Answers – Rotary Compressor

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Rotary Compressor”.

1. Rotary compressors are used where ____ quantities of gas are needed at relatively ____ pressure.
a) large, high
b) large, low
c) small, high
d) small, low

Explanation: This is where rotary compressors are used.

2. Rotary compressor can be classified as
a) displacement compressor
c) both of the mentioned
d) none of the mentioned

Explanation: These are the two types of rotary compressor.

3. In steady-flow compressor, compression occurs by
a) transfer of kinetic energy
b) transfer of potential energy
c) trapping air
d) all of the mentioned

Explanation: The transfer of kinetic energy occurs from a rotor.

4. In displacement compressor, compression occurs by
a) transfer of kinetic energy
b) transfer of potential energy
c) trapping air
d) all of the mentioned

Explanation: Here air is compressed by trapping it in reducing space.

5. The rotary positive displacement machines are ____ and compression is ____
a) cooled, isothermal
b) uncooled, isothermal

Explanation: These are uncooled and adiabatic compression takes place.
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6. The Roots blower and vane-type compressor are the types of
a) displacement compressor
c) both of the mentioned
d) none of the mentioned

Explanation: These are the two types of rotary positive displacement machines.

7. For a Root blower, as pressure ratio increases, efficiency ____
a) increases
b) decreases
c) remains constant
d) none of the mentioned

Explanation: This can be seen by taking pressure ratios and calculating efficiencies for them.

8. The vane type compressor requires ____ the Roots blower.
a) equal work input
b) more work input
c) less work input
d) none of the mentioned

Explanation: This is true for given air flow and pressure ratio.

9. The centrifugal and axial flow compressor are the types of
a) displacement compressor
c) both of the mentioned
d) none of the mentioned

Explanation: These are the two types of steady-flow compressors.

10. Which of the following is true for a centrifugal compressor?
a) rotation of impeller compresses the air
b) diffuser converts part of KE into internal energy
c) typical pressure ratio is around 1.4 to 1
d) all of the mentioned

Explanation: This is the working of a centrifugal compressor.

11. Which of the following is true for an axial-flow compressor?
a) blades are arranged in same manner as in reaction turbine
b) flow of air is along the axis of compressor
c) velocity of air changes when it passes through the blades
d) all of the mentioned

Explanation: This is the working of an axial-flow compressor.

12. For uncooled rotary compressor, compression process is ____ while ideal process is ____

Explanation: The isentropic process is reversible and adiabatic.

13. In an adiabatic irreversible process, extra work is done to overcome friction.
a) true
b) false