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Compressors, Gas Turbines & Jet Engines MCQ Solved Paper for SBI PO

Thursday 9th of March 2023

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1. Isothermal compression efficiency, even when running at high speed, can be approached by using
A. Multistage compression
B. Cold water spray
C. Both (A) and (B) above
D. Fully insulating the cylinder
Answer : C
2. 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
3. The thermodynamic efficiency of rotary compressor is based on
A. Isothermal compression
B. Adiabatic compression
C. Isentropic compression
D. Polytropic compression
Answer : B
4. To avoid moisture troubles, the compressed air main line should
A. Rise gradually towards the point of use
B. Drop gradually towards the point of use
C. Be laid vertically
D. Be laid exactly horizontally
Answer : B
5. 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
6. The absolute pressure of air at the outlet of a compressor is called
A. Back pressure
B. Critical pressure
C. Discharge pressure
D. None of these
Answer : C
7. The efficiency of jet engine is
A. Lower at low speed
B. Higher at high altitudes
C. Same at all altitudes
D. Higher at high speed
Answer : B
8. If p? is the pressure of air entering the L.P, cylinder and p? is the pressure of air leaving the H.P. cylinder, then the ratio of cylinder diameters for a single acting, two stage reciprocating compressor with complete intercooling is given by
A. D?/D? = (p? p?)1/2
B. D?/D? = (p?/p?)1/4
C. D?/D? = (p? p?)1/4
D. D?/D? = (p?/p?)1/4
Answer : D
9. 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
10. 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
11. The thermal efficiency of a gas turbine as compared to a diesel plant is
A. Same
B. More
C. Less
D. Depends on other factors
Answer : C
12. Air-fuel ratio in a jet engine will be of the order of
A. 10 : 1
B. 15 : 1
C. 20 : 1
D. 60 : 1
Answer : D
13. The type of rotary compressor used in aeroplanes, is of
A. Centrifugal type
B. Axial flow type
C. Radial flow type
D. None of these
Answer : B
14. 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
15. The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
A. 75 %
B. 85 %
C. 90 %
D. 99 %
Answer : D
16. 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
17. Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
A. Higher
B. Lower
C. Equal
D. Cant be compared
Answer : B
18. 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
19. The air entry velocity m a rocket as compared to aircraft is
A. Same
B. More
C. Less
D. Zero
Answer : D
20. The temperature of air at the beginning of the compression stroke is ________ the atmospheric temperature.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : C
21. The maximum propulsion efficiency of a turbojet is attained at around following speed
A. 550 km/hr
B. 1050 km/hr
C. 1700 km/hr
D. 2400 km/hr
Answer : D
22. In a closed cycle gas turbine, the air is compressed
A. Isothermally
B. Polytropically
C. Isentropically
D. None of these
Answer : C
23. The efficiency of roots blower ________ with the increase in pressure ratio.
A. Decreases
B. Increases
C. Does not change
D. None of these
Answer : A
24. Which is false statement about air receivers?
A. These are used to dampen pulsations
B. These act as reservoir to take care of sudden demands
C. These increase compressor efficiency
D. These knock out some oil and moisture
Answer : C
25. If the flow of air through the compressor is perpendicular to its axis, then it is a
A. Reciprocating compressor
B. Centrifugal compressor
C. Axial flow compressor
D. Turbo compressor
Answer : B
26. Axial flow compressor resembles
A. Centrifugal pump
B. Reciprocating pump
C. Turbine
D. Sliding vane compressor
Answer : C
27. The volumetric efficiency of a compressor
A. Increases with decrease in compression ratio
B. Decreases with decrease in compression ratio
C. Increases with increase in compression ratio
D. Decreases with increase in compression ratio
Answer : D
28. 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 : D
29. The maximum combustion pressure in gas turbine as compared to I.C. engine is
A. More
B. Less
C. Same
D. Depends on other factors
Answer : B
30. The ratio of specific weight/h.p. of gas turbine and I.C engines may be typically of the order of
A. 1 : 1
B. 2 : 1
C. 4 : 1
D. 1 : 6
Answer : D
31. 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 : A
32. The work ratio of a gas turbine plant is defined as the ratio of
A. Net work output and heat supplied
B. Net work output and work done by turbine
C. Actual heat drop and isentropic heat drop
D. Net work output and isentropic heat drop
Answer : B
33. Gas turbines for power generation are normally used
A. To supply base load requirements
B. To supply peak load requirements
C. To enable start thermal power plant
D. In emergency
Answer : B
34. 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
35. 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
36. Clearance volume in actual reciprocating compressors is essential
A. To accommodate Valves in the cylinder head
B. To provide cushioning effect
C. To attain high volumetric efficiency
D. To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head
Answer : D
37. Free air is the air at
A. Atmospheric conditions at any specific location
B. 20°C and 1 kg/cm² and relative humidity of 36%
C. 0°C and standard atmospheric conditions
D. 15°C and 1 kg/cm²
Answer : A
38. For perfect intercooling in a two stage compressor
A. p?/p? = p?/p?
B. p?/p? = p?/p?
C. p? = p?
D. p? = p? p?
Answer : A
39. 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
40. 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
41. The intercooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p? = Intake pressure of air, p? = Intercooler pressure, and p? = Delivery pressure of air)
A. p? = p? × p?
B. p? = p?/p?
C. p? = p? × p?
D. p? = p?/p?
Answer : C
42. Inter-cooling in multistage compressors is done
A. To cool the air during compression
B. To cool the air at delivery
C. To enable compression in two stages
D. To minimise the work of compression
Answer : D
43. The maximum temperature in a gas turbine is
A. 200°C
B. 500°C
C. 700°C
D. 1000°C
Answer : C
44. 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
45. The axial flow compressor is preferred in aircraft gas turbines because of
A. Low frontal area
B. Higher thrust
C. High pressure rise
D. None of these
Answer : A
46. The workdone on a compressor will be minimum if air is taken from
A. The atmosphere
B. A source at 0°C
C. A source of low temperature air
D. A source of high temperature air
Answer : C
47. Fighter bombers use following type of engine
A. Turbojet
B. Turbo-propeller
C. Rocket
D. Ramjet
Answer : A
48. Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on
A. Mass flow rate
B. Pressure ratio
C. Change in load
D. Stagnation pressure at the outlet
Answer : D
49. Losses in a centrifugal compressor are due to
A. Inlet losses
B. Impeller channel losses
C. Diffuser losses
D. All of the above
Answer : D
50. In the axial flow gas turbine, the work ratio is the ratio of
A. Compressor work and turbine work
B. Output and input
C. Actual total head temperature drop to the isentropic total head drop from total head inlet to static head outlet
D. Actual compressor work and theoretical compressor work
Answer : C

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