IIFT - Compressors, Gas Turbines & Jet Engines 1000+ MCQ [Solved] PDF Download

1. If V, U and Vr represent the absolute velocity of fluid, velocity of blade, and relative velocity of fluid, and suffix I and o stand for entry and exit conditions, then in a rotary machine whose degree of reaction is unity
A. V_i = V_o
B. V_t > V_o
C. U < V_o
D. V = U_o
Answer : A

2. Stalling of blades in axial flow compressor is the phenomenon of
A. Air stream blocking the passage
B. Motion of air at sonic velocity
C. Unsteady periodic and reversed flow
D. Air stream not able to follow the blade contour
Answer : D

3. High air-fuel ratio is used in gas turbines
A. To increase the output
B. To increase the efficiency
C. To save fuel
D. To reduce the exit temperature
Answer : D

4. Reheating in multistage expansion gas turbine results in
A. High thermal efficiency
B. Reduction in compressor work
C. Decrease of heat loss in exhaust
D. Maximum work output
Answer : D

5. 1 m of air at atmospheric condition weighs approximately
A. 0.5 kg
B. 1.0 kg
C. 1.3 kg
D. 2.2 kg
Answer : C

6. Separators in compressor installations are located
A. Before intercooler
B. After intercooler
C. After receiver
D. Between after-cooler and air receiver
Answer : D

7. Ratio of indicated H.P. and brake H.P. is known as
A. Mechanical efficiency
B. Volumetric efficiency
C. Isothermal efficiency
D. Adiabatic efficiency
Answer : A

8. If infinite number of heaters be used in a gas turbine, then expansion process in turbine approaches
A. Isothermal
B. Isentropic
C. Adiabatic
D. Isochoric
Answer : A

9. 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

10. In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to
A. N.T.P. conditions
B. Intake temperature and pressure conditions
C. 0°C and 1 kg/cm²
D. 20°C and 1 kg/cm²
Answer : B

11. For slow speed large capacity compressor, following type of valve will be best suited
A. Poppet valve
B. Mechanical valve of the Corliss, sleeve, rotary or semi rotary type
C. Disc or feather type
D. Any of the above
Answer : C

12. The maximum compression ratio in an actual single stage axial flow compressor is of the order of
A. 1 : 1.2
B. 1 : 2
C. 1 : 5
D. 1 : 10
Answer : A

13. The thermodynamic efficiency of rotary compressor is based on
A. Isothermal compression
B. Adiabatic compression
C. Isentropic compression
D. Polytropic compression
Answer : B

14. Gas turbine works on
A. Brayton or Atkinson cycle
B. Carnot cycle
C. Rankine cycle
D. Erricson cycle
Answer : A

15. Pressure ratio in gas turbines is the ratio of
A. Compressor pressure ratio
B. Highest pressure to exhaust pressure
C. Inlet pressure to exhaust pressure
D. Pressures across the turbine
Answer : B

16. Which of the following statement is correct?
A. The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency
B. The compression ratio for the compressor is always greater than unity
C. The compressor capacity is the ratio of workdone per cycle to the stroke volume
D. During isothermal compression of air, the workdone in a compressor is maximum
Answer : B

17. The ratio of isentropic work to Eulers work is known as
A. Compressor efficiency
B. Isentropic efficiency
C. Euler's efficiency
D. Pressure coefficient
Answer : D

18. The ratio of isentropic work to Euler work is known as
A. Pressure coefficient
B. Work coefficient
C. Polytropic reaction
D. Slip factor
Answer : A

19. 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

20. Gas turbines use following type of air compressor
A. Centrifugal type
B. Reciprocating type
C. Lobe type
D. Axial flow type
Answer : D

21. In n? and n? are the indices of compression for the first and second stage of compression, then the ratio of workdone on the first and second stages (W?/W?) with perfect intercooling is given by
A. W?/W? = n?(n? - 1)/n?(n? - 1)
B. W?/W? = n?(n? - 1)/n?(n? - 1)
C. W?/W? = n?/n?
D. W?/W? = n?/n? Answer : B

22. The degree of reaction is usually kept ________ for all types of axial flow compressors.
A. 0.2
B. 0.3
C. 0.4
D. 0.5
Answer : D

23. The gas in cooling chamber of a closed cycle gas turbine is cooled at
A. Constant volume
B. Constant temperature
C. Constant pressure
D. None of these
Answer : C

24. Out of the following, from where you will prefer to take intake for air compressor
A. From an air conditioned room maintained at 20°C
B. From outside atmosphere at 1°C
C. From coal yard side
D. From a side where cooling tower is located nearby
Answer : D

25. The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is
A. Less
B. More
C. Same
D. More/less depending on compressor capacity
Answer : B

26. 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 : D

27. Efficiency of gas turbine is increased by
A. Reheating
B. Inter cooling
C. Adding a regenerator
D. All of the above
Answer : C

28. The compressor efficiency is the
A. Isothermal H.P/indicated H.R
B. Isothermal H.P./shaft H.R
C. Total output/air input
D. Compression work/motor input
Answer : A

29. A large clearance volume in a reciprocating compressor results in
A. Reduced volume flow rate
B. Increased volume flow rate
C. Lower suction pressure
D. Lower delivery pressure
Answer : A

30. An air compressor may be controlled by
A. Throttle control
B. Clearance control
C. Blow off control
D. Any one of the above
Answer : D

31. The performance of air compressor at high altitudes will be ________ as compared to that at sea level.
A. Same
B. Lower
C. Higher
D. None of these
Answer : B

32. The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is
A. Heated
B. Compressed air before entering the combustion chamber is heated
C. Bled gas from turbine is heated and readmitted for complete expansion
D. Exhaust gases drive the compressor
Answer : B

33. Rotary compressors are used for delivering
A. Small quantities of air at high pressures
B. Large quantities of air at high pressures
C. Small quantities of air at low pressures
D. Large quantities of air at low pressures
Answer : D

34. The overall efficiency of the compressed air system is the
A. Ratio of shaft output of the air motor to the shaft input to the compressor
B. Ratio of shaft input to the compressor to the shaft output of air motor
C. Product of shaft output of air motor and shaft input to the compressor
D. None of the above
Answer : A

35. The working fluid in a turbine is
A. In two phases
B. In three phases
C. In a single phase
D. In the form of air and water mixture
Answer : C

36. Pick up the correct statement
A. Gas turbine uses low air-fuel ratio to economise on fuel
B. Gas turbine uses high air-fuel ratio to reduce outgoing temperature
C. Gas turbine uses low air-fuel ratio to develop the high thrust required
D. All of the above
Answer : B

37. The compression ratio in a gas turbine is of the order of
A. 3.5 : 1
B. 5 : 1
C. 8 : 1
D. 12 : 1
Answer : C

38. 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

39. In a closed cycle gas turbine, the air is compressed
A. Isothermally
B. Polytropically
C. Isentropically
D. None of these
Answer : C

40. Pick up the wrong statement
A. Pulsejet requires no ambient air for propulsion
B. Ramjet engine has no turbine
C. Turbine drives compressor in a Turbojet
D. Bypass turbojet engine increases the thrust without adversely affecting, the propulsive efficiency and fuel economy
Answer : A

41. The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
A. Compression ratio
B. Work ratio
C. Pressure ratio
D. None of these
Answer : B

42. High air-fuel ratio in gas turbines
A. Increases power output
B. Improves thermal efficiency
C. Reduces exhaust temperature
D. Do not damage turbine blades
Answer : C

43. Water is injected in gas turbine cycle to
A. Control temperature
B. Control output of turbine
C. Control fire hazards
D. Increase efficiency
Answer : B

44. The output of a gas turbine is 300 KW and its efficiency is 20 percent, the heat supplied is
A. 6000 KW
B. 15 KW
C. 600 KW
D. 150 KW
Answer : B

45. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
A. Pressure drop across the valves
B. Superheating in compressor
C. Clearance volume and leakages
D. All of these
Answer : D

46. The volume of air delivered by the compressor is called
A. Free air delivery
B. Compressor capacity
C. Swept volume
D. None of these
Answer : B

47. The mean effective pressure of the compressor is the
A. Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
B. Volume of air delivered by the compressor
C. Volume of air sucked by the compressor during its suction stroke
D. None of the above
Answer : D

48. In an axial flow compressor, the ratio of pressure in the rotor 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 : C

49. In jet engines the products of combustion after passing through the gas turbine are discharged into
A. Atmosphere
B. Back to the compressor
C. Discharge nozzle
D. Vacuum
Answer : C

50. To avoid moisture troubles, the branch connections from compressed air lines should be taken from
A. Top side of main
B. Bottom side of main
C. Left side of main
D. Right side of main
Answer : A