Mechanical Engineering : Compressors, Gas Dynamics and Gas Turbines MCQs with Answers

1 .
The maximum temperature in a gas turbine is
A)  250°C
B)  500°C
C)  700°C
D)  1000°C

Correct Answer :   700°C

2 .
The fuel consumption in gas turbines is accounted for by
A)  Heating value
B)  Higher heating value
C)  Higher calorific value
D)  Lower heating value

Correct Answer :   Lower heating value

3 .
The type of rotary compressor used in aeroplanes, is of
A)  axial flow type
B)  radial flow type
C)  centrifugal type
D)  None of the above

Correct Answer :   axial flow type

4 .
An axial compressor gives optimum performance at high speeds and large volume flows.
A)  Agree
B)  Disagree
C)  Can Not Say
D)  None of the above

Correct Answer :   Agree

5 .
The degree of reaction in an axial flow compressor is defined as the ratio of static enthalpy rise in the
A)  stator to static enthalpy rise in the rotor
B)  rotor to static enthalpy rise in the stage
C)  rotor to static enthalpy rise in the stator
D)  stator to static enthalpy rise in the stage

Correct Answer :   rotor to static enthalpy rise in the stage

6 .
The compression ratio for the compressor is always _________ unity.
A)  Equal to
B)  Less than
C)  More than
D)  None of the above

Correct Answer :   More than

Explanation : The compression ratio is simply the ratio of the absolute stage discharge pressure to the absolute stage suction pressure.

The compression ratio for the compressor is always More than unity.

7 .
In a reciprocating air compressor, the compression work per kg of air
A)  increases as clearance volume increases
B)  is independent of clearance volume
C)  increases as clearance volume decreases
D)  decreases as clearance volume increases

Correct Answer :   is independent of clearance volume

8 .
The volume of air sucked by the compressor during its suction stroke is called
A)  swept volume
B)  free air delivery
C)  compressor capacity
D)  None of the above

Correct Answer :   swept volume

9 .
The volumetric efficiency of a compressor
A)  increases with increase in compression ratio
B)  constant with decrease in compression ratio
C)  decreases with decrease in compression ratio
D)  decreases with increase in compression ratio

Correct Answer :   decreases with increase in compression ratio

10 .
Reheating in a multi-stage expansion gas turbine __________ compressor work.
A)  increases
B)  decreases
C)  has no effect on
D)  None of the above

Correct Answer :   decreases

11 .
For perfect intercooling in a two stage compressor,
A)  p₁=p₃
B)  p₁ = p₂ p₃
C)  p₂/p₁ = p₃/p₂
D)  p₁/p₃ = p₂/p₁

Correct Answer :   p₂/p₁ = p₃/p₂

12 .
Continuous flow of fluid is called as _______
A)  Continuum
B)  Invincible flow
C)  Continuum & Invincible flow
D)  None of the above

Correct Answer :   Continuum

13 .
Knudsen number does not have any __________
A)  units
B)  dimension
C)  units & dimension
D)  None of the above

Correct Answer :   dimension

Explanation : Knudsen number does not have any dimension and units.

14 .
The hottest point in a gas turbine is
A)  At the tip
B)  At the base
C)  In the center
D)  Between ~ to i of the blade height

Correct Answer :   Between ~ to i of the blade height

Explanation : The hottest point in a gas turbine is between ~ to i of the blade height.

The hottest component is the turbine blades, in particular the first-stage turbine inlet guide vanes, which are the most forward part of the exhaust section of the engine, which is the section exposed to the hot exhaust gases.

15 .
In a jet propulsion
A)  Its functioning does not depend upon presence of air
B)  The propulsive matter is ejected from within the propelled body
C)  Both (A) and (B)
D)  The propulsive matter is caused to flow around the propelled body

Correct Answer :   The propulsive matter is caused to flow around the propelled body

Explanation : Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction.

By Newton's third law, the moving body is propelled in the opposite direction to the jet.

16 .
Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
A)  Higher
B)  Equal
C)  Lower
D)  Can't be compared

Correct Answer :   Lower

17 .
In a compressed air system, the temperature of air discharged from the air motor is __________ than the initial compressor intake temperature.
A)  less
B)  more
C)  Can't be compared
D)  None of the above

Correct Answer :   less

18 .
The efficiency of roots blower __________ with the increase in pressure ratio.
A)  decreases
B)  increases
C)  does not change
D)  None of the above

Correct Answer :   decreases

19 .
A jet engine has
A)  propeller at back
B)  no propeller
C)  propeller in front
D)  propeller on the top

Correct Answer :   no propeller

20 .
A compressor at high altitudes will require __________ power.
A)  less
B)  same
C)  more
D)  None of the above

Correct Answer :   less

21 .
The thrust of a jet propulsion power unit can be increased by
A)  burning fuel after gas turbine
B)  injecting water into the compressor
C)  injecting ammonia into the combustion chamber
D)  All of the above

Correct Answer :   All of the above

22 .
The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is
A)  superheating in compressor
B)  pressure drop across the valves
C)  clearance volume and leakages
D)  All of the above

Correct Answer :   All of the above

23 .
The indicated work per unit mass of air delivered is
A)  Greatly affected by clearance volume
B)  Inversely proportional to clearance volume
C)  Not affected by clearance volume
D)  Directly proportional to clearance volume

Correct Answer :   Not affected by clearance volume

24 .
Gas turbine blades are given a rake
A)  Equal to zero
B)  In the direction of motion of blades
C)  Depending on the velocity
D)  Opposite to the direction of motion of blades

Correct Answer :   In the direction of motion of blades

25 .
In jet engines, for the efficient production of large power, fuel is burnt in an atmosphere of
A)  Compressed air
B)  Vacuum
C)  Oxygen alone
D)  Atmospheric air

Correct Answer :   Compressed air

26 .
Continuum in fluids is predicted by using _______
A)  Mach number
B)  Knudsen & Mach number
C)  Knudsen number
D)  None of the above

Correct Answer :   Knudsen number

27 .
Ratio of mean free path to characteristic length is called as _________
A)  Knudsen number
B)  Mach number
C)  Nusselt number
D)  None of the above

Correct Answer :   Knudsen number

Explanation : Ratio of mean free path to characteristic length is called Knudsen number. Nusselt number is used in heat transfer.

28 .
An aftercooler is used to
A)  cool the air
B)  reduce volume of air
C)  remove impurities from air
D)  cause moisture and oil vapour to drop out

Correct Answer :   cause moisture and oil vapour to drop out

29 .
The ratio of the indicated power to the shaft power or brake power of the motor or engine required to drive the compressor, is called
A)  volumetric efficiency
B)  mechanical efficiency
C)  isothermal efficiency
D)  compressor efficiency

Correct Answer :   mechanical efficiency

30 .
If p₁, is the pressure of air entering the L.P. cylinder and p₁ is the pressure of air leaving the L.P. cylinder (or intercooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D₁ = Dia. of L.P. cylinder, and D₂ = Dia. of H.P. cylinder)
A)  D₁/D₂ = √p₁p₂
A)  
B)  D₁/D₂ = √p₁/p₂
B)  
C)  D₁/D₂ = √p₂/p₁
C)  
D)  None of the above
D)  

Correct Answer :   D₁/D₂ = √p₂/p₁

31 .
The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as
A)  isothermal efficiency
B)  mechanical efficiency
C)  volumetric efficiency
D)  compressor efficiency

Correct Answer :   volumetric efficiency

32 .
The multi-stage compression ofair as compared to single stage compression
A)  gives more uniform torque
B)  reduces workdone per kg of air
C)  improves volumetric efficiency for the given pressure ratio
D)  All of the above

Correct Answer :   All of the above

33 .
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)  degree of reaction
B)  slip factor
C)  work factor
D)  pressure coefficient

Correct Answer :   degree of reaction

34 .
Which one of the following is the effect of blade shape on performance of a centrifugal compressor?
A)  Forward curved blades has higher efficiency
B)  Forward curved blades produce lower pressure ratio
C)  Backward curved blades has poor efficiency
D)  Backward curved blades lead to stable performance

Correct Answer :   Forward curved blades produce lower pressure ratio

35 .
In a jet engine, the air-fuel ratio is
A)  30:1
B)  40:1
C)  50:1
D)  60:1

Correct Answer :   60:1

36 .
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)  Radial blades
B)  Forward curved blades
C)  Backward curved blades
D)  All of the above

Correct Answer :   Forward curved blades

37 .
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
A)  
B)  more than
B)  
C)  Can Not Say
C)  
D)  None of the above
D)  

Correct Answer :   less than

38 .
The velocity of air entering in a rocket is __________ as compared to an aircraft.
A)  less
B)  more
C)  zero
D)  same

Correct Answer :   zero

39 .
The ratio of the discharge pressure to the inlet pressure of air is called
A)  compression ratio
B)  expansion ratio
C)  volumetric efficiency
D)  compressor efficiency

Correct Answer :   compression ratio

40 .
Which of the following statement is correct relating to rocket engines?
A)  The stagnation conditions exist at the combustion chamber
B)  The exit velocities of exhaust gases are much higher than those in jet engine
C)  The combustion chamber in a rocket engine is directly analogous to the reservoir of a super sonic wind tunnel
D)  All of the above

Correct Answer :   All of the above

41 .
In reciprocating air compressors, isothermal efficiency is used for all sorts of calculations.
A)  Correct
B)  Incorrect
C)  Can Not Say
D)  None of the above

Correct Answer :   Correct

42 .
A rocket engine uses __________ for the combustion of its fuel.
A)  surrounding air
B)  its own oxygen
C)  compressed atmospheric air
D)  None of the above

Correct Answer :   its own oxygen

43 .
Euler's equation can be used for
A)  pumps
B)  axial flow compressors
C)  radial flow compressors
D)  All of the above

Correct Answer :   All of the above

44 .
Free air is the air at atmospheric conditions at any specific location.
A)  True
B)  False
C)  Can Not Say
D)  None of the above

Correct Answer :   True

45 .
Air motors work on the cycle which is the reverse of the reciprocating air compressor cycle.
A)  Agree
B)  Disagree
C)  Can Not Say
D)  None of the above

Correct Answer :   Agree

46 .
A closed cycle gas turbine works on
A)  Carnot cycle
B)  Rankine cycle
C)  Joule cycle
D)  Ericsson cycle

Correct Answer :   Joule cycle

47 .
Which of the following statement is correct?
A)  The reciprocating compressors are best suited for high pressure and low volume capacity
A)  
B)  The effect of clearance volume on power consumption is negligible for the same volume of discharge
B)  
C)  Both (A) and (B)
C)  
D)  None of the above
D)  

Correct Answer :   Both (A) and (B)

48 .
The air power of the compressor is also known as
A)  brake power
B)  indicated power
C)  frictional power
D)  None of the above

Correct Answer :   indicated power

49 .
A turbo-prop is preferred to turbo-jet because
A)  it can fly at high elevations
B)  it can fly at super sonic speeds
C)  it has high propulsive efficiency at high speeds
D)  it has high power for take off

Correct Answer :   it has high power for take off

50 .
The ratio of the isentropic work to the Euler's work is known as pressure coefficient.
A)  Yes
B)  No
C)  Can Not Say
D)  None of the above

Correct Answer :   Yes

51 .
When the outlet angle from the rotor of a centrifugal compressor is more than 90°, then the blades are said to be
A)  radial
B)  forward curved
C)  backward curved
D)  None of the above

Correct Answer :   forward curved

52 .
In a high pressure compressor, the delivery pressure is
A)  1 to 5 bar
B)  5 to 8 bar
C)  8 to 10 bar
D)  10 to 15 bar

Correct Answer :   8 to 10 bar

53 .
The overall isothermal efficiency of the compressor is defined as the ratio of
A)  isentropic power to the power required to drive the compressor
B)  volume of free air delivery per stroke to the swept volume of the piston
C)  isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor
D)  work required to compress the air isothermally to the actual work required to compress the air for the same pressure ratio

Correct Answer :   isothermal power to the shaft power or B.P. of the motor or engine required to drive the compressor

54 .
The minimum work required for a three stage reciprocating air compressor is __________ the work required for each stage.
A)  equal to
B)  double
C)  three times
D)  six times

Correct Answer :   three times

55 .
The compression ratio in a gas turbine is
A)  1
B)  4
C)  9
D)  12

Correct Answer :   1

56 .
Only rocket engines can be propelled to space because
A)  they can generate very high thrust
B)  they are not air-breathing engines
C)  they have high propulsion efficiency
D)  these engines can work on several fuels

Correct Answer :   they are not air-breathing engines

57 .
A large clearance Volume in a reciprocating compressor results in
A)  lower suction pressure
B)  lower delivery pressure
C)  increased volume flow rate
D)  reduced volume flow rate

Correct Answer :   reduced volume flow rate

58 .
When the temperature of air leaving the intercooler, in a two stage compression with intercooler, is __________ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.
A)  less than
A)  
B)  equal to
B)  
C)  more than
C)  
D)  None of the above
D)  

Correct Answer :   equal to

59 .
A closed cycle gas turbine gives __________ efficiency as compared to an open cycle gas turbine.
A)  higher
B)  same
C)  lower
D)  None of the above

Correct Answer :   higher

60 .
Intercooling in gas turbines
A)  increases net output and thermal efficiency both
B)  decreases net output and thermal efficiency both
C)  increases net output but decreases thermal efficiency
D)  decreases net output but increases thermal efficiency

Correct Answer :   increases net output but decreases thermal efficiency

61 .
Gas turbine as compared to steam turbine
A)  has less efficiency
B)  requires less space for installation
C)  has compressor and combustion chamber
D)  All of the above

Correct Answer :   All of the above

62 .
In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into
A)  vacuum
B)  discharge nozzle
C)  atmosphere
D)  back to the compressor

Correct Answer :   discharge nozzle

63 .
A compressor mostly used for supercharging of I.C. engines is
A)  roots blower
B)  radial flow compressor
C)  axial flow compressor
D)  reciprocating compressor

Correct Answer :   radial flow compressor

64 .
The workdone on a compressor will be minimum if air is taken from
A)  a source at 0° C
B)  the atmosphere
C)  a source of low temperature air
D)  a source of high temperature air

Correct Answer :   a source of low temperature air

65 .
A closed cycle gas turbine consists of a
A)  compressor
B)  cooling chamber
C)  heating chamber
D)  All of the above

Correct Answer :   All of the above

66 .
The intercooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by (where p₁ = Intake pressure of air, p₂ = Intercooler pressure, and p₃ = Delivery pressure of air)
A)  p₂ = √p₁ x p₃
A)  
B)  p₂ = p₃/p₁
B)  
C)  p₂ = p₁/p₃
C)  
D)  p₂ = p₁ x p₃
D)  

Correct Answer :   p₂ = √p₁ x p₃

67 .
The pressure ratio in a centrifugal compressor can be increased by increasing the tip speed and lowering the inlet temperature.
A)  Correct
B)  Incorrect
C)  Can Not Say
D)  None of the above

Correct Answer :   Correct

68 .
The pressure of air at the beginning of the compression stroke is __________ the atmospheric pressure.
A)  less than
B)  equal to
C)  more than
D)  None of the above

Correct Answer :   less than

69 .
In axial flow compressors, the flow of air is parallel to the axis of compressor.
A)  Correct
B)  Incorrect
C)  Can Not Say
D)  None of the above

Correct Answer :   Correct

70 .
In a double acting compressor, the air is compressed
A)  in one cylinder
B)  in a single cylinder on both sides of the piston
C)  in two cylinders
D)  in two cylinders on both sides of the piston

Correct Answer :   in a single cylinder on both sides of the piston

71 .
In a centrifugal compressor, the flow of air is __________ to the axis of compressor.
A)  parallel
B)  inclined
C)  perpendicular
D)  None of the above

Correct Answer :   perpendicular

72 .
For minimum work required to compress and deliver a quantity of air by multi-stage compression,
A)  the intercooling should be perfect
B)  the workdone in each stage should be same
C)  the compression ratio in each stage should be same
D)  All of the above

Correct Answer :   All of the above

73 .
The propulsive power of the rocket is (where v₁ = Jet velocity, and v₂ = Air-craft velocity)
A)  v₁² - v₂² / g
A)  
B)  (v₁ - v₂)² / g
B)  
C)  v₁² - v₂² / 2g
C)  
D)  (v₁ - v₂)² / 2g
D)  

Correct Answer :   v₁² - v₂² / 2g

74 .
In air compressors, free air delivery means 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

Correct Answer :   actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions

75 .
Separators are generally used in air compressor installations
A)  after the intercooler
B)  before the intercooler
C)  before first stage suction
D)  between the aftercooler and receiver

Correct Answer :   between the aftercooler and receiver

76 .
If the flow of air through the compressor is perpendicular to its axis, then it is a
A)  turbo compressor
B)  centrifugal compressor
C)  axial flow compressor
D)  reciprocating compressor

Correct Answer :   centrifugal compressor

77 .
With the decrease in compression ratio, the volumetric efficiency
A)  increases
B)  decreases
C)  does not change
D)  None of the above

Correct Answer :   increases

78 .
The assumption made in two stage compression with intercooler is that
A)  there is no pressure drop in the intercooler
B)  the compression in both the cylinders is polytropic
C)  the suction and delivery of air takes place at constant pressure
D)  All of the above

Correct Answer :   All of the above

79 .
The compression ratio for the compressor is always __________ unity.
A)  less than
B)  equal to
C)  more than
D)  None of the above

Correct Answer :   more than

80 .
A 3 m³/min compressor means that it
A)  compresses 3 m³/min of standard air
B)  compresses 3 m³/ min of free air
C)  delivers 3 m³/ min of compressed air
D)  delivers 3 m³/ min of compressed air at delivery pressure

Correct Answer :   compresses 3 m³/ min of free air

81 .
In axial flow compressor, exit flow angle deviation from the blade angle is a function of
A)  blade camber
B)  space-chord ratio
C)  blade camber and incidence angle
D)  blade camber and space-chord ratio

Correct Answer :   blade camber and incidence angle

82 .
Rotary compressors are used for delivering
A)  large quantities of air at low pressures
B)  small quantities of air at low pressures
C)  small quantities of air at high pressures
D)  large quantities of air at high pressures

Correct Answer :   large quantities of air at low pressures

83 .
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

Correct Answer :   increase in flow and decrease in efficiency

84 .
A rotary compressor is driven by an
A)  engine
B)  electric motor
C)  Either (A) and (B)
D)  None of the above

Correct Answer :   Either (A) and (B)

85 .
The temperature of air at the beginning of the compression stroke is __________ the atmospheric temperature.
A)  less than
B)  equal to
C)  more than
D)  None of the above

Correct Answer :   more than

86 .
Gas turbine as compared to internal combustion engine
A)  has more efficiency
B)  produces uniform torque
C)  can be driven at a very high speed
D)  All of the above

Correct Answer :   All of the above

87 .
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)  efficiency of the engine
B)  thrust and range of aircraft
C)  Both (A) and (B)
D)  None of the above

Correct Answer :   thrust and range of aircraft

88 .
The axial flow compressor is preferred in air-craft gas turbines because of
A)  higher thrust
B)  high pressure rise
C)  low frontal area
D)  None of the above

Correct Answer :   low frontal area

89 .
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
C)  Can Not Say
D)  None of the above

Correct Answer :   True

90 .
The ratio of the net work obtained from the gas turbine plant to the turbine work is known as
A)  work ratio
B)  pressure ratio
C)  compression ratio
D)  None of the above

Correct Answer :   work ratio

91 .
Which of the following statement is correct as regard to centrifugal compressors?
A)  The impeller rotates at high speeds.
B)  The flow of air is parallel to the axis of the compressor.
C)  The maximum efficiency is higher than multi-stage axial flow compressors.
D)  The static pressure of air in the impeller increases in order to provide centripetal force on the air.

Correct Answer :   The static pressure of air in the impeller increases in order to provide centripetal force on the air.

92 .
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 the above

Correct Answer :   0.15 to 5 m³/s

93 .
In a closed cycle gas turbine, the air is compressed
A)  isothermally
B)  polytropically
C)  isentropically
D)  None of the above

Correct Answer :   isentropically

94 .
If the flow of air through the compressor is parallel to its axis, then the compressor is
A)  turbo-compressor
B)  axial flow compressor
C)  centrifugal compressor
D)  reciprocating compressor

Correct Answer :   axial flow compressor

95 .
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 the above

Correct Answer :   isothermal compression

96 .
The speed of rotary air compressor is __________ as compared to reciprocating air compressor.
A)  high
B)  low
C)  Can Not Say
D)  None of the above

Correct Answer :   high

97 .
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

Correct Answer :   0.5

98 .
When air is to be compressed at a high pressure, then it is advantageous to use
A)  single stage compression
B)  multi-stage compression without intercooling
C)  multi-stage compression with intercooling
D)  None of the above

Correct Answer :   multi-stage compression with intercooling

99 .
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 the above

Correct Answer :   discharge pressure

100 .
Which of the following statement is correct?
A)  The compressor capacity is the ratio of workdone per cycle to the stroke volume.
A)  
B)  The compression ratio for the compressor is always greater than unity.
B)  
C)  During isothermal compression of air, the workdone in a compressor is maximum.
C)  
D)  The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency.
D)  

Correct Answer :   The compression ratio for the compressor is always greater than unity.

101 .
The efficiency of a jet engine is higher at
A)  low speeds
B)  high altitudes
C)  low altitudes
D)  high speeds

Correct Answer :   high altitudes

102 .
The volume of air delivered by the compressor is called
A)  swept volume
B)  compressor capacity
C)  free air delivery
D)  None of the above

Correct Answer :   compressor capacity

103 .
The type of rotary compressor used in gas turbines, is of
A)  axial flow type
B)  radial flow type
C)  centrifugal type
D)  None of the above

Correct Answer :   axial flow type

104 .
In the aircraft propellers
A)  its functioning does not depend upon the presence of air
B)  the propulsive matter is caused to flow around the propelled body
C)  Both (A) and (B)
D)  the propulsive matter is ejected from within the propelled body

Correct Answer :   the propulsive matter is ejected from within the propelled body

105 .
Intercooling in multi-stage compressors is done
A)  to cool the air at delivery
B)  to cool the air during compression
C)  to minimise the work of compression
D)  to enable compression in two stages

Correct Answer :   to minimise the work of compression

106 .
The inlet pressure is always __________ the discharge pressure.
A)  less than
B)  equal to
C)  more than
D)  None of the above

Correct Answer :   less than

107 .
The ratio of workdone per cycle to the stroke volume of the compressor is known as
A)  compression ratio
B)  mean effective pressure
C)  compressor capacity
D)  compressor efficiency

Correct Answer :   mean effective pressure

108 .
For a two stage reciprocating compressor, compression from p₁ to p₃ 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 p₂ is given by
A)  p₂ = pa p₃/p₁
A)  
B)  p₂ = √p₁.p₃
B)  
C)  p₂ = Pa x p₃/p₁
C)  
D)  p₂ = (p₁ + p₃)/2
D)  

Correct Answer :   p₂ = √p₁.p₃

109 .
A machine used to raise the pressure of air is called
A)  I.C engine
B)  air motor
C)  compressor
D)  gas turbine

Correct Answer :   compressor

110 .
The overall efficiency of the compressed air system is the
A)  ratio of shaft input to the compressor to the shaft output of air motor
B)  product of shaft output of air motor and shaft input to the compressor
C)  Both (A) and (B)
D)  ratio of shaft output of the air motor to the shaft input to the compressor

Correct Answer :   ratio of shaft output of the air motor to the shaft input to the compressor

111 .
In a single acting reciprocating air compressor, without clearance, the compression of air may be
A)  polytropic
B)  isentropic
C)  isothermal
D)  any one of these

Correct Answer :   any one of these

112 .
The performance of air compressor at high altitudes will be __________ as compared to that at sea level.
A)  lower
B)  same
C)  higher
D)  None of the above

Correct Answer :   lower

113 .
In a centrifugal compressor, the highest Mach number leading to shock wave in the fluid flow occurs at
A)  impeller inlet radius
B)  diffuser outlet radius
C)  diffuser inlet radius
D)  impeller outlet radius

Correct Answer :   diffuser outlet radius

114 .
The air is delivered __________ in one revolution in case of a three-lobbed rotor.
A)  three times
B)  four times
C)  six times
D)  None of the above

Correct Answer :   six times

115 .
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

Correct Answer :   one-sixth

116 .
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)  outlet velocity of flow
D)  inlet velocity of flow

Correct Answer :   outlet velocity of flow

117 .
In a turbo jet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in
A)  turbine blades, which is essentially an isentropic process
B)  exit nozzle, which is a constant volume process
C)  turbine blades, which is a constant volume process
D)  exit nozzle, which is essentially an isentropic process

Correct Answer :   turbine blades, which is essentially an isentropic process

118 .
The compressor capacity is defined as the
A)  volume of air sucked by the compressor during its suction stroke
B)  volume of air delivered by the compressor
C)  actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
D)  None of the above

Correct Answer :   volume of air delivered by the compressor

119 .
Standard air is the air at __________ and relative humidity of 36 percent.
A)  1 bar and 40° C
B)  1 bar and 20° C
C)  0.1 bar and 40° C
D)  0.1 bar and 20° C

Correct Answer :   1 bar and 20° C

120 .
In a single stage, single acting reciprocating air compressor without clearance volume, the workdone is maximum during
A)  polytropic compression
B)  isothermal compression
C)  isentropic compression
D)  None of the above

Correct Answer :   isentropic compression

121 .
Which of the following statement is wrong?
A)  In a two stage reciprocating air compressor with complete intercooling, maximum work is saved.
A)  
B)  The minimum work required for a two stage reciprocating air compressor is double the work required for each stage.
B)  
C)  The ratio of the volume of free air delivery per stroke to the swept volume of the piston is called volumetric efficiency.
C)  
D)  None of the above
D)  

Correct Answer :   None of the above

122 .
The capacity of a compressor is expressed in
A)  m³/min
B)  m³/kg
C)  kg/m²
D)  kg/m³

Correct Answer :   m³/min

123 .
In a single acting reciprocating compressor, the suction, compression and delivery of air takes place in __________ of the piston.
A)  one stroke
B)  two strokes
C)  three strokes
D)  four strokes

Correct Answer :   two strokes

124 .
he maximum delivery pressure in a rotary air compressor is
A)  10 bar
B)  20 bar
C)  30 bar
D)  50 bar

Correct Answer :   10 bar

125 .
The stagnation pressure rise in a centrifugal compressor takes place
A)  in the diffuser only
B)  in the impeller only
C)  in the inlet guide vanes only
D)  in the diffuser and impeller

Correct Answer :   in the diffuser and impeller

126 .
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 T₁ to T₂ at a constant pressure.
A)  equal to
A)  
B)  less than
B)  
C)  greater than
C)  
D)  None of the above
D)  

Correct Answer :   equal to

127 .
Reheating in a gas turbine
A)  increases the turbine work
B)  increases the compressor work
C)  increases the thermal efficiency
D)  decreases the thermal efficiency

Correct Answer :   increases the thermal efficiency

128 .
Workdone by an air compressor __________ upon the way in which the air is compressed.
A)  depends
B)  does not depend
C)  Can Not Say
D)  None of the above

Correct Answer :   depends

129 .
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
C)  Can Not Say
D)  None of the above

Correct Answer :   Agree

130 .
If p1 is the pressure of air entering the L.P, cylinder and p3 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)  D1/D2 = (p1p3)1/4
A)  
B)  D1/D2 = (p3/p1)1/4
B)  
C)  D1/D2 = (p1p3)1/2
C)  
D)  D1/D2 = (p1/p3)1/4
D)  

Correct Answer :   D1/D2 = (p3/p1)1/4

131 .
In a four stage compressor, if the pressure at the first and third stage are 1 bar and 16 bar, then the delivery pressure at the fourth stage will be
A)  1 bar
B)  16 bar
C)  64 bar
D)  256 bar

Correct Answer :   64 bar

132 .
The volumetric efficiency for reciprocating air compressors is about
A)  10 to 40%
B)  40 to 60%
C)  60 to 70%
D)  70 to 90%

Correct Answer :   70 to 90%

133 .
A rocket works with maximum overall efficiency when air-craft velocity is __________ the jet velocity.
A)  equal to
B)  one-half
C)  double
D)  None of the above

Correct Answer :   one-half

134 .
When altitude of earth is in between 90 km and 150 km Knudsen number can be in between 0.3 and _________
A)  1
B)  2
C)  3
D)  4

Correct Answer :   1

Explanation : When altitude of earth is in between 90 km and 150 km Knudsen number can be in between 0.3 and 1.

135 .
Knudsen number ranges in between 0.3 and 1 in ________
A)  boundary region
B)  boundary & transient region
C)  transient region
D)  None of the above

Correct Answer :   transient region

Explanation : Knudsen number ranges in between 0.3 and 1 in transient region.

136 .
The work ratio of simple gas turbine cycle depends on
A)  Pressure ratio
B)  Minimum cycle temperature
C)  Maximum cycle temperature
D)  All of the above

Correct Answer :   All of the above

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