Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 3 :: Mechanical Engineering

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Q1. In a closed cycle gas turbine, the air is compressed

(A) Isothermally
(B) Polytropically
(C) Isentropically
(D) None of these

Answer:(C) Isentropically

Q2. The efficiency and work ratio of a gas turbine plant can be increased by

(A) Adding heat exchanger
(B) Injecting water in/around combustion chamber
(C) Reheating the air after partial expansion in the turbine
(D) All of the above

Answer: (D) All of the above

Q3. In a double acting compressor, the air is compressed

(A) In one cylinder
(B) In two cylinders
(C) In a single cylinder on both sides of the piston
(D) In two cylinders on both sides of the piston

Answer: (C) In a single cylinder on both sides of the piston

Q4. The ratio of work done per cycle to the swept volume in case of compressor is called

(A) Compression index
(B) Compression ratio
(C) Compressor efficiency
(D) Mean effective pressure

Answer:(D) Mean effective pressure

Q5. A machine used to raise the pressure of air is called

(A) Gas turbine
(B) I.C engine
(C) Compressor
(D) Air motor

Answer: (C) Compressor

Q6. Ratio of compression is the ratio of

(A) Gauge discharge pressure to the gauge intake pressure
(B) Absolute discharge pressure to the absolute intake pressure
(C) Pressures at discharge and suction corresponding to same temperature
(D) Stroke volume and clearance volume

Answer: (B) Absolute discharge pressure to the absolute intake pressure

Q7. The thrust on the rotor in a centrifugal compressor is produced by

(A) Radial component
(B) Axial component
(C) Tangential component
(D) None of the above

Answer: (B) Axial component

Q8. Reheating in a gas turbine

(A) Increases the thermal efficiency
(B) Increases the compressor work
(C) Increases the turbine work
(D) Decreases the thermal efficiency

Answer: (A) Increases the thermal efficiency

Q9. The volume of air delivered in a medium capacity air compressor per unit time is

(A) 0.1 to 1.2 m³/s
(B) 0.15 to 5 m³/s
(C) Above 5 m³/s
(D) None of these

Answer: (B) 0.15 to 5 m³/s

Q10. A turboprop is preferred to turbojet because

(A) It has high propulsive efficiency at high speeds
(B) It can fly at supersonic speeds
(C) It can fly at high elevations
(D) It has high power for take off

Answer: (D) It has high power for take off

Q11. The closed cycle in gas turbines

(A) Provides greater flexibility
(B) Provides lesser flexibility
(C) In never used
(D) Is used when gas is to be burnt

Answer:(A) Provides greater flexibility

Q12. The capacity of compressor will be highest when its intake temperature is

(A) Lowest
(B) Highest
(C) Anything
(D) Atmospheric

Answer: (D) Atmospheric

Q13. After-cooler is used to

(A) Cool the air
(B) Decrease the delivery temperature for ease in handling
(C) Cause moisture and oil vapour to drop out
(D) Reduce volume

Answer: (C) Cause moisture and oil vapour to drop out

Q14. Intercooling in gas turbines

(A) Decreases net output but increases thermal efficiency
(B) Increases net output but decreases thermal efficiency
(C) Decreases net output and thermal efficiency both
(D) Increases net output and thermal efficiency both

Answer: (D) Increases net output and thermal efficiency both

Q15. The capacity of a compressor is 5 m/min refers to

(A) Standard air
(B) Free air
(C) Compressed air
(D) Compressed air at delivery pressure

Answer: (B) Free air

Q16. The compressed air may be used

(A) In gas turbine plants
(B) For operating pneumatic drills
(C) In starting and supercharging of I.C. engines
(D) All of the above

Answer: (D) All of the above

Q17. In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow occurs at

(A) Diffuser inlet radius
(B) Diffuser outlet radius
(C) Impeller inlet radius
(D) Impeller outlet radius

Answer: (B) Diffuser outlet radius

Q18. Pick up the wrong statement about advantages of multistage compression

(A) Better lubrication is possible advantages of multistage
(B) More loss of air due to leakage past the cylinder
(C) Mechanical balance is better
(D) Air can be cooled perfectly in between

Answer: (B) More loss of air due to leakage past the cylinder

Q19. For a two stage compressor, if index of compression for higher stage is greater than index of compression for lower stage, then the optimum pressure as compared to ideal case will

(A) Increase
(B) Decrease
(C) Remain unaffected
(D) Other factors control it

Answer: (A) Increase

Q20. Axial flow compressor resembles

(A) Centrifugal pump
(B) Reciprocating pump
(C) Turbine
(D) Sliding vane compressor

Answer: (C) Turbine

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