1000+ Compressors, Gas Turbines & Jet Engines Multiple Choice Question Answer [Solved]

1. The criterion of the thermodynamic efficiency for rotary compressor is
A. Isentropic compression
B. Isothermal compression
C. Polytropic compression
D. None of the above
Answer : A

2. Which of the following plants is smallest and lightest for generating a given amount of power?
A. Gas turbine plant
B. Petrol engine
C. Diesel engine
D. Solar plant
Answer : A

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

4. The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is
A. Low
B. High
C. Same
D. Low/high depending on make and type
Answer : A

5. In multistage compressor, the isothermal compression is achieved by
A. Employing intercooler
B. By constantly cooling the cylinder
C. By running compressor at very slow speed
D. By insulating the cylinder
Answer : C

6. 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

7. Standard air is the air at
A. Atmospheric conditions at any specific location
B. 20°C and 1 kg/cm² and relative humidity 36%
C. 0°C and standard atmospheric conditions
D. 15°C and 1 kg/cm²
Answer : B

8. Pick up the wrong statement
A. Centrifugal compressors deliver practically constant pressure over a considerable range of capacities
B. Axial flow compressors have a substantially constant delivery at variable pressures
C. Centrifugal compressors have a wider stable operating range than axial flow compressors
D. Axial flow compressors are bigger in diameter compared to centrifugal type
Answer : D

9. For supplying intermittent small quantity of air at high pressure, following compressor is best suited
A. Centrifugal
B. Reciprocating
C. Axial
D. Screw
Answer : B

10. Choose the correct statement
A. Gas turbine requires lot of cooling water
B. Gas turbine is capable of rapid start up and loading
C. Gas turbines has flat efficiency at part loads
D. Gas turbines have high standby losses and require lot of maintenance
Answer : B

11. 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

12. Open cycle gas turbine works on
A. Brayton or Atkinson cycle
B. Rankine cycle
C. Carnot cycle
D. Erricson cycle
Answer : A

13. The stagnation pressure rise in a centrifugal compressor takes place
A. In the diffuser only
B. In the impeller only
C. In the diffuser and impeller
D. In the inlet guide vanes only
Answer : C

14. During base load operation, the best method of controlling compressor is
A. Start-stop motor
B. Constant speed unloader
C. Relief valve
D. Variable speed
Answer : A

15. Isothermal compression though most efficient, but is not practicable because
A. It requires very big cylinder
B. It does not increase pressure much
C. It is impossible in practice
D. Compressor has to run at very slow speed to achieve it
Answer : D

16. 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

17. A rotary compressor is driven by an
A. Electric motor
B. Engine
C. Either (A) or (B)
D. None of these
Answer : C

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

19. 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

20. Axial flow compressor resembles
A. Centrifugal pump
B. Reciprocating pump
C. Turbine
D. Sliding vane compressor
Answer : C

21. 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 efficency and fuel economy
Answer : A

22. Gas turbine blades are given a rake
A. Equal to zero
B. In the direction of motion of blades
C. Opposite to the direction of motion of blades
D. Depending on the velocity
Answer : B

23. 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

24. The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)
A. r ^?-1
B. 1 - r ^?-1
C. 1 - (1/r) ^?-1/?
D. 1 - (1/r) ^?/?-1
Answer : C

25. A centrifugal compressor works on the principle of
A. Conversion of pressure energy into kinetic energy
B. Conversion of kinetic energy into pressure energy
C. Centripetal action
D. Generating pressure directly
Answer : B

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

27. When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be
A. Forward curved
B. Backward curved
C. Radial
D. None of these
Answer : A

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

29. The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called
A. Slip factor
B. Velocity factor
C. Velocity coefficient
D. None of the above
Answer : A

30. The compressor performance at higher altitude compared to sea level will be
A. Same
B. Higher
C. Lower
D. Dependent on other factors
Answer : C

31. For a two stage reciprocating compressor, compression from p? to p? is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p? is given by
A. p? = (p? + p?)/2
B. p? = p?. p?
C. P? = Pa × p?/p?
D. p? = Pa p?/p?
Answer : B

32. Pick up the false statement
A. Gas turbine is a self starting unit
B. Gas turbine does not require huge quantity of water like steam plant
C. Exhaust losses in gas turbine are high due to large mass flow rate
D. Overall efficiency of gas turbine plant is lower than that of a reciprocating engine
Answer : A

33. The air-fuel ratio in gas turbines is of the order of
A. 7 : 1
B. 15 : 1
C. 30 : 1
D. 50 : 1.
Answer : D

34. Work ratio of a gas turbine may be improved by
A. Decreasing the compression work
B. Increasing the compression work
C. Increasing the turbine work
D. Both (A) and (C) above
Answer : D

35. In a centrifugal compressor, an increase in speed at a given pressure ratio causes
A. Increase in flow
B. Decrease in flow
C. Increase in efficiency
D. Increase in flow and decrease in efficiency
Answer : D

36. 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

37. Euler's equation can be used for
A. Radial flow compressors
B. Axial flow compressors
C. Pumps
D. All of these
Answer : D

38. When air is to be compressed at a high pressure, then it is advantageous to use
A. Single stage compression
B. Multistage compression without intercooling
C. Multistage compression with intercooling
D. None of these
Answer : C

39. A simple turbojet engine is basically
A. A propeller system
B. Gas turbine engine equipped with a propulsive nozzle and diffuse
C. Chemical rocket engine
D. Ramjet engine
Answer : B

40. 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

41. The material commonly used for air craft gas turbine is
A. Stainless steel
B. High alloy steel
C. Duralumin
D. Timken, Haste alloys
Answer : D

42. 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

43. A compressor at high altitude will draw
A. More power
B. Less power
C./strong> Same power
D. More/less power depending on other factors
Answer : B