70 + Mcqs in Compressors, Gas Dynamics and Gas Turbines Page 1 McqOptions

1.	For perfect intercooling in a two stage compressor,
A.	=
B.	=
C.
Answer» B. =

Discussion

2.	Reheating in a multi-stage expansion gas turbine __________ compressor work.
A.	has no effect on
B.	decreases
C.	increases
Answer» C. increases

Discussion

3.	A compressor at high altitudes will require __________ power.
A.	same
B.	less
C.	more
Answer» C. more

Discussion

4.	For minimum work in multi-stage compression, the workdone on all stages should be equal.
A.	Yes
B.	No
Answer» B. No

Discussion

5.	Free air is the air at atmospheric conditions at any specific location.
A.	True
B.	False
Answer» B. False

Discussion

6.	A gas turbine used in air-craft should have low weight and small frontal area.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

7.	The clearance, in a single stage, single acting reciprocating air compressor does not effect the workdone on the air and the power required for compressing the air.
A.	True
B.	False
Answer» B. False

Discussion

8.	Air motors work on the cycle which is the reverse of the reciprocating air compressor cycle.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

9.	Which of the following statement is correct relating to rocket engines ?
A.	The combustion chamber in a rocket engine is directly analogous to the reservoir of a super sonic wind tunnel
B.	The stagnation conditions exist at the combustion chamber
C.	The exit velocities of exhaust gases are much higher than those in jet engine
D.	all of the above
Answer» E.

Discussion

10.	In reciprocating air compressors, isothermal efficiency is used for all sorts of calculations.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

11.	The perfect intercooling, in multistage compression, means that the temperature of air at inlet to subsequent stages is equal to the initial temperature.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

12.	The pressure ratio in a centrifugal compressor can be increased by increasing the tip speed and lowering the inlet temperature.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

13.	The compressor efficiency is defined as the ratio of volume of free air delivery per stroke to the swept volume of the piston.
A.	Correct
B.	Incorrect
Answer» C.

Discussion

14.	In a gas turbine, air is obtained from the atmosphere and compressed in an air compressor.
A.	True
B.	False
Answer» B. False

Discussion

15.	The temperature of air at the beginning of the compression stroke is __________ the atmospheric temperature.
A.	equal to
B.	less than
C.	more than
Answer» D.

Discussion

16.	For perfect intercooling in a three stage compressor,
A.	=
B.	=
Answer» B. =

Discussion

17.	In a jet engine, the compression varies as the square of the speed.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

18.	The process, which causes the air to enter the impeller blades of a centrifugal compressor at __________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.
A.	reduced
B.	increased
Answer» B. increased

Discussion

19.	In jet propulsion power unit, the inlet duct of diverging shape is used for converting kinetic energy of air into pressure energy.
A.	True
B.	False
Answer» B. False

Discussion

20.	The axial flow compressor is preferred in air-craft gas turbines because of
A.	low frontal area
B.	higher thrust
C.	high pressure rise
D.	none of these
Answer» B. higher thrust

Discussion

21.	The pressure of air at the beginning of the compression stroke is __________ the atmospheric pressure.
A.	equal to
B.	less than
C.	more than
Answer» C. more than

Discussion

22.	In open cycle turbo-jet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the
A.	thrust and range of aircraft
B.	efficiency of the engine
C.	both (a) and (b)
D.	none of these
Answer» B. efficiency of the engine

Discussion

23.	In a single stage, single acting reciprocating air compressor, without clearance volume, the workdone is minimum during
A.	isothermal compression
B.	isentropic compression
C.	polytropic compression
D.	none of these
Answer» B. isentropic compression

Discussion

24.	In a single stage, single acting reciprocating air compressor without clearance volume, the workdone is maximum during
A.	isothermal compression
B.	isentropic compression
C.	polytropic compression
D.	none of these
Answer» C. polytropic compression

Discussion

25.	In a single stage, single acting reciprocating air compressor, without clearance, the workdone on the air during isentropic compression is __________ the heat required to raise the temperature of air from to at a constant pressure.
A.	equal to
B.	less than
C.	greater than
Answer» B. less than

Discussion

26.	In a compressed air system, the temperature of air discharged from the air motor is __________ than the initial compressor intake temperature.
A.	more
B.	less
Answer» C.

Discussion

27.	The performance of air compressor at high altitudes will be __________ as compared to that at sea level.
A.	same
B.	lower
C.	higher
Answer» C. higher

Discussion

28.	In a centrifugal compressor, the air enters the impeller axially and leaves the vane radially.
A.	Yes
B.	No
Answer» C.

Discussion

29.	In gas turbines, the work input with intercooling is __________ the work input with no intercooling.
A.	less man
B.	more than
Answer» B. more than

Discussion

30.	The compressor capacity will be __________ if the temperature of intake air is lowest.
A.	lowest
B.	highest
Answer» C.

Discussion

31.	The efficiency of roots blower __________ with the increase in pressure ratio.
A.	decreases
B.	increases
C.	does not change
Answer» B. increases

Discussion

32.	The operation of lifts, rams and pumps make use of compressed air.
A.	Yes
B.	No
Answer» B. No

Discussion

33.	A receiver in compressor installations is used to damp pressure waves in compressor discharge.
A.	Yes
B.	No
Answer» B. No

Discussion

34.	Maximum work is saved in a two stage reciprocating air compressor with incomplete intercooling.
A.	Agree
B.	Disagree
Answer» C.

Discussion

35.	The mass of gas turbine per kW developed is about __________ as that of an I.C. engine.
A.	same
B.	one-half
C.	one-fourth
D.	one-sixth
Answer» E.

Discussion

36.	In a centrifugal compressor, the ratio of the __________ to the blade velocity is called slip factor.
A.	inlet whirl velocity
B.	outlet whirl velocity
C.	inlet velocity of flow
D.	outlet velocity of flow
Answer» E.

Discussion

37.	The air is delivered __________ in one revolution in case of a three-lobbed rotor.
A.	two times
B.	three times
C.	four times
D.	six times
Answer» E.

Discussion

38.	Workdone by an air compressor __________ upon the way in which the air is compressed.
A.	depends
B.	does not depend
Answer» B. does not depend

Discussion

39.	In a compressor, work is done on the piston during suction of air and work is done by the piston during compression as well as delivery of air.
A.	Agree
B.	Disagree
Answer» B. Disagree

Discussion

40.	Which one of the following is the effect of blade shape on performance of a centrifugal compressor ?
A.	Backward curved blades has poor efficiency
B.	Backward curved blades lead to stable performance
C.	Forward curved blades has higher efficiency
D.	Forward curved blades produce lower pressure ratio
Answer» E.

Discussion

41.	Which of the following bladings will give maximum pressure rise in a centrifugal compressor, assuming the same overall dimensions, blade inlet angle and rotational speeds ?
A.	Forward curved blades
B.	Backward curved blades
C.	Radial blades
D.	all of these
Answer» B. Backward curved blades

Discussion

42.	In an axial flow compressor, the ratio of pressure in theTOtor blades to the pressure rise in the compressor in one stage is known as
A.	work factor
B.	slip factor
C.	degree of reaction
D.	pressure coefficient
Answer» D. pressure coefficient

Discussion

43.	The free air delivery is the volume of air that can be delivered by a compressor freely.
A.	True
B.	False
Answer» C.

Discussion

44.	The multi-stage compression ofair as compared to single stage compression
A.	improves volumetric efficiency for the given pressure ratio
B.	reduces workdone per kg of air
C.	gives more uniform torque
D.	all of these
Answer» E.

Discussion

45.	For minimum work required to compress and deliver a quantity of air by multi-stage compression,
A.	the compression ratio in each stage should be same
B.	the intercooling should be perfect
C.	the workdone in each stage should be same
D.	all of the above
Answer» E.

Discussion

46.	In a two stage reciprocating compressor with intercooler, the amount of work saved with incomplete intercooling is __________ that in case of complete intercooling.
A.	less than
B.	more than
Answer» B. more than

Discussion

47.	A regenerator in a gas turbine improves thermal efficiency.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

48.	The velocity of air entering in a rocket is __________ as compared to an aircraft.
A.	zero
B.	less
C.	more
D.	same
Answer» B. less

Discussion

49.	In axial flow compressors, the flow of air is parallel to the axis of compressor.
A.	Correct
B.	Incorrect
Answer» B. Incorrect

Discussion

50.	The ratio of the isothermal power to the shaft power or brake power of the motor or engine required to drive the compressor is called overall isothermal efficiency.
A.	True
B.	False
Answer» B. False

Discussion

Explore topic-wise MCQs in Mechanical Engineering.

For perfect intercooling in a two stage compressor,

Reheating in a multi-stage expansion gas turbine __________ compressor work.

A compressor at high altitudes will require __________ power.

For minimum work in multi-stage compression, the workdone on all stages should be equal.

Free air is the air at atmospheric conditions at any specific location.

A gas turbine used in air-craft should have low weight and small frontal area.

The clearance, in a single stage, single acting reciprocating air compressor does not effect the workdone on the air and the power required for compressing the air.

Air motors work on the cycle which is the reverse of the reciprocating air compressor cycle.

Which of the following statement is correct relating to rocket engines ?

In reciprocating air compressors, isothermal efficiency is used for all sorts of calculations.

The perfect intercooling, in multistage compression, means that the temperature of air at inlet to subsequent stages is equal to the initial temperature.

The pressure ratio in a centrifugal compressor can be increased by increasing the tip speed and lowering the inlet temperature.

The compressor efficiency is defined as the ratio of volume of free air delivery per stroke to the swept volume of the piston.

In a gas turbine, air is obtained from the atmosphere and compressed in an air compressor.

The temperature of air at the beginning of the compression stroke is __________ the atmospheric temperature.

For perfect intercooling in a three stage compressor,

In a jet engine, the compression varies as the square of the speed.

The process, which causes the air to enter the impeller blades of a centrifugal compressor at __________ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.

In jet propulsion power unit, the inlet duct of diverging shape is used for converting kinetic energy of air into pressure energy.

The axial flow compressor is preferred in air-craft gas turbines because of

The pressure of air at the beginning of the compression stroke is __________ the atmospheric pressure.

In open cycle turbo-jet engines used in military aircraft, reheating the exhaust gas from the turbine by burning, more fuel is used to increase the

In a single stage, single acting reciprocating air compressor, without clearance volume, the workdone is minimum during

In a single stage, single acting reciprocating air compressor without clearance volume, the workdone is maximum during

In a single stage, single acting reciprocating air compressor, without clearance, the workdone on the air during isentropic compression is __________ the heat required to raise the temperature of air from to at a constant pressure.

In a compressed air system, the temperature of air discharged from the air motor is __________ than the initial compressor intake temperature.

The performance of air compressor at high altitudes will be __________ as compared to that at sea level.

In a centrifugal compressor, the air enters the impeller axially and leaves the vane radially.

In gas turbines, the work input with intercooling is __________ the work input with no intercooling.

The compressor capacity will be __________ if the temperature of intake air is lowest.

The efficiency of roots blower __________ with the increase in pressure ratio.

The operation of lifts, rams and pumps make use of compressed air.

A receiver in compressor installations is used to damp pressure waves in compressor discharge.

Maximum work is saved in a two stage reciprocating air compressor with incomplete intercooling.

The mass of gas turbine per kW developed is about __________ as that of an I.C. engine.

In a centrifugal compressor, the ratio of the __________ to the blade velocity is called slip factor.

The air is delivered __________ in one revolution in case of a three-lobbed rotor.

Workdone by an air compressor __________ upon the way in which the air is compressed.

In a compressor, work is done on the piston during suction of air and work is done by the piston during compression as well as delivery of air.

Which one of the following is the effect of blade shape on performance of a centrifugal compressor ?

Which of the following bladings will give maximum pressure rise in a centrifugal compressor, assuming the same overall dimensions, blade inlet angle and rotational speeds ?

In an axial flow compressor, the ratio of pressure in theTOtor blades to the pressure rise in the compressor in one stage is known as

The free air delivery is the volume of air that can be delivered by a compressor freely.

The multi-stage compression ofair as compared to single stage compression

For minimum work required to compress and deliver a quantity of air by multi-stage compression,

In a two stage reciprocating compressor with intercooler, the amount of work saved with incomplete intercooling is __________ that in case of complete intercooling.

A regenerator in a gas turbine improves thermal efficiency.

The velocity of air entering in a rocket is __________ as compared to an aircraft.

In axial flow compressors, the flow of air is parallel to the axis of compressor.

The ratio of the isothermal power to the shaft power or brake power of the motor or engine required to drive the compressor is called overall isothermal efficiency.