Compressors, Gas
Turbines and Jet Engines -
Mechanical Engineering Multiple
choice Questions and Answers
1. 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
(e) 25°C, 1 kg/cm2 and relative humidity of 50%.
Ans: a
2. 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
(e) 25°C, 1 kg/cm2 and RH of 60%.
Ans: b
3. 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
(e) 3.2 kg.
Ans: c
4. Adiabatic compression is one in which
(a) temperature during compression remains
constant
(b) no heat leaves or enters the compressor
cylinder during cornpression
(c) temperature rise follows a linear relationship
(d) work done is maximum
(e) entropy decreases.
Ans: b
5. The capacity of a compressor is 5 m /mih. 5 m /
min refers to
(a) standard air
(b) free air
(c) compressed air
(d) compressed air at delivery pressure
(e) air sucked.
Ans: b
6. The overall isothermal eiffciency of compressor
is defined as the ratio of
(a) isothermal h.p. to the BHP of motor
(b) isothermal h.p. to adiabatic h.p.
(c) power to drive compressor to isothermal h.p.
(d) work to compress air isothermally to work for
actual compression
(e) isothermal work to ideal work.
Ans: a
7. The- most efficient method of compressing air is
to compress it
(a) isothermally
(b) adiabatically
(c) isentropically
(d) isochronically
(e) as per law pV
Ans: a
8. Maximum work is done in compressing air when
the compression is
(a) isothermal
(b) adiabatic
(c) polytropic
(d) any one of the above
(e) none of the above.
Ans: b
9. The pressure and temperature conditions of air at
the suction of compressor are
(a) atmospheric
(b) slightly more than atmospheric
(c) slightly less than atmospheric
(d) pressure slightly more than atmospheric and
temperature slightly less than atmospheric
(e) pressure sightly less than atmospheric and
temperature slightly more than atmospheric.
Ans: e
10. Isothermal compression effeicency can be
attained by running the compressor
(a) at very high speed
(b) at very slow speed
(c) at average speed
(d) at zero speed
(e) isothermally.
Ans: b
11. The compressor capacity with decrease in
suction temperature
(a) increases
(b) decreases
(c) remains unaffected
(d) may increase or decrease depending on
compressor capacity
(e) increases upto certain limit and then decreases.
Ans: a
12. Isothermal compression efficiency, even when
running at high speed, can be approached by using
(a) multi-stage compression
(b) cold water spray
(c) both (a) and (b) above
(d) fully insulating the cylinder
(e) high stroke.
Ans: c
13. Compression efficiency is compared against
(a) ideal compression
(b) adiabatic compression
(c) botii isothermal and adiabatic compression
(d) isentropic compression
(e) isothermal compression.
Ans: e
14. Aeroplanes employ following type of
compressor
(a) radial flow
(b) axial flow
(c) centrifugal
(d) combination of above
(e) none of the above.
Ans: b
15. Inter cooling in compressors
(a) cools the delivered air
(b) results in saving of power in compressing a
given volume to given pressure
(c) is the standard practice for big compressors
(d) enables compression in two stages
(e) prevents compressor jacket running very hot.
Ans: b
16. An ideal air compressor cycle without clearance
on p-v diagram can be represented by following
processes
(a) one adiabatic, two isobaric, and one constant
volume
(b) two adiabatic and two isobaric
(c) two adiabatic, one isobaric and one constant
volume
(d) one adiabatic, one isobaric and two constant
volume
(e) two isobaric, two adiabatic and one constant
volume.
Ans: a
17. An ideal air compressor cycle with clearance on
p-v diagram can be represented by following
processes
(a) one adiabatic, two isobaric, and one constant
volume
(b) two adiabatic and two isobaric
(c) two adiabatic, one isobaric and one constant
volume,
(d) one adiabatic, one isobaric and two constant
volume
(e) two isobaric, two adiabatic and one constant
volume.
Ans: b
18. What will be the volume of air at 327°C if its
volume at 27°C is 1.5 m3/mt
(a) 3 m3/mt .
(b) 1.5 m3/mt
(c) 18 m3/mt'
(d) 6 m3/mt
(e) 0.75 m3/mt.
Ans: a
19. The work done per unit mass of air in
compression will'be least when n is equal to
(a) 1
(b) 1.2 ,
(c) 1.3
(d) 1.4
(e) 1.5
Ans: a
20. Isothermal compression though most efficient,
but is not -practicable because
(a) ityrequires 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
(e) it requires cylinder to be placed in water.
Ans: d
21. Ratio of indicated H.P. and brake H.P. is known
as
(a) mechanical efficiency
(b) volumetric efficiency
(c) isothermal efficiency
(d) adiabatic efficiency
(e) relative efficiency.
Ans: a
22. The ratio of work doen 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
(e) compressor effectiveness.
Ans: d
23. Cylinder clearance in a compressor should be
(a) as large as possible
(b) as small as possible
(c) about 50% of swept volume
(d) about 100% of swept volume
(e) none of the above.
Ans: b
24. Ratio of compression is the ratio of
(a) gauge discharge pressure to the gauge intake
pressure
(b) absolute discharge pressure to the ab-solute
intake pressure
(c) pressures at discharge and suction cor-
responding to same temperature
(d) stroke volume and clearance volume
(e) none of the above.
Ans: b
25. Clearance volume in actual reciprocating
compressors is essential
(a) to accommedate Valves in the cylinder head
(b) to provide cushioning effect
(c) to attain high volumetric efficiency
(d) to avoid mechanical bang of piston with cylinder
head
(e) to provide cushioning effect and also to avoid
mechanical bang of piston with cylinder head.
Ans: e
26. The net work input required for compressor with
increase in clearance volume
(a) increases
(b) decreases
(c) remains same
(d) increases/decreases depending on com-
pressor capacity
(e) unpredictable.
Ans: c
27. Ratio of indicated h.p. to shaft h.p. in known as
(a) compressor efficiency
(b) isothermal efficiency
(c) volumetric efficiency
(d) mechanical efficiency
(e) adiabatic efficiency.
Ans: d
28. Volumetric efficiency is
(a) the ratio of stroke volume to clearance volume
(b) the ratio of the air actually delivered to the
amount of piston displacement
(c) reciprocal of compression ratio
(d) index of compressor performance
(e) proportional to compression ratio.
Ans: b
29. Volumetric efficiency of air compressors is of
the order of
(a) 20-30%
(b) 40-50%
(c) 60-70%
(d) 70-90%
(e) 90-100%.
Ans: d
30. Volumetric efficiency of a compressor with
clearance volume
(a) increases with increase in compression ratio
(b) decreases with increase in compression ratio
(c) in not dependent upon compression ratio
(d) may increase/decrease depending on
compressor capacity
(e) unpredictable.
Ans: b
31. Volumetric efficiency of a compressor without
clearance volume
(a) increases with increase in compression ratio
(b) decreases with increase in compression ratio
(c) is not dependent upon compressin ratio
(d) may increase/decrease depending on
compressor capacity
(e) unpredictable.
Ans: c
32. The clearance volume of the air compressor is
kept minimum because
(a) it allows maximum compression to be achieved
(b) it greatly affects volumetric efficiency
(c) it results in minimum work
(d) it permits isothermal compression
(e) none of the above.
Ans: b
33. Euler's equation is applicable for
(a) centrifugal compressor
(b) axial compressor
(c) pumps
(d) all of the above
(e) none of the above.
Ans: d
40. 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
(e) from any one of the above locations.
Ans: d
41. Mining industry usually employs following
motive power
(a) A.C. electric motor
(b) compressed air
(c) petrol engine
(d) diesel engine
(e) D.C. electric motor.
Ans: b
42. 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
(e) These reduce frequent on/off operation of
compressors.
Ans: c
44. An air receiver is to be placed outside. Should it
be placed in
(a) sun
(b) shade
(c) rain
(d) enclosed room
(e) anywhere.
Ans:
45. Which is false statement about multistage
compression .
(a) Power consumption per unit of air delivered is
low
(b) Volumetric efficiency is high
(c) It is best suited for compression ratios around
7:1
(d) The moisture in air is condensed in the
intercooler
(e) Outlet temperature is reduced.
Ans: b
46. 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
(e) none of the above.
Ans: c
47. Reciprocating air compressor is best suited for
(a) large quantity of air at high pressure
(b) small quantity of air at high pressure
(c) small quantity of air at low pressure
(d) large quantity of air at low pressure
(e) any one of the above.
Ans: a
48. Rotary compressor is best suited for
(a) large quantity of air at high pressure
(b) small quantity of air at high pressure
(c) small quantity of air at low pressure
(d) large quantity of air at low pressure
(e) any one of the above.
Ans: b
49. The capacity of compressor will be highest
when its intake temperature is
(a) lowest
(b) highest
(c) anything.
(d) atmospheric
(e) none of the above.
Ans: d
50. 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
(e) increase pressure.
Ans: c
51. To aviod 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
(e) none of the above
Ans: b
52. Separators in compressor installations are
located
(a) before intercooler
(b) after intercooler
(c) after receiver
(d) between after-cooler and air receiver
(e) before suction.
Ans: d
53. 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
(e) unpredictable.
Ans: b
54. An air compressor may be controlled by
(a) throttle control (b) clearance control
(c) blow-off control
(d) any one of the above
(e) none of the above.
Ans: d
55. The compressor efficiecny 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
(e) none Of the above.
Ans: a
56. 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
(e) any location.
Ans: a
57. The thrust on the rotor in a centrifugal
compressor is produced by
(a) radial component
(b) axial component
(c) tangential component
(d) resultant component
Ans: b
58. The compressor performance at higher altitude
compared to sea level will be
(a) same
(b) higher
(c) lower
(d) dependent on other factors
(e) none of the above.
Ans: c
59. A compressor at high altitude will draw
(a) more power
(b) less power
(c) same power
(d) more/less power depending on other factors
(e) none of the above.
Ans: b
60. During peak load periods, the best method of
controlling compressors is
(a) start-stop motor
(b) constant speed unloader
(c) relief valve
(d) variable speed
(e) none of the above.
Ans: b
61. A centrifugal compressor works on the principle
of
(a) conversion of pressure energy into kinetic
energy
(b) conversion of kinetic energy into pres¬sure
energy
(c) centripetal action
(d) generating pressure directly
(e) combination of (a) and (d).
Ans: b
62. For a compressor, least work will be done if the
compression is
(a) isentropic
(b) isothermal
(c) polytropic
(d) somewhere in between isentropic and
isothermal
(e) none of the above.
Ans: b
67. In a compressor, free air delivered is the actual
volume delivered at the stated pressure reduced to
(d) N.T.P. conditions
(b) intake temperature and pressure conditions
(c) 0°C and 1 kg/cm2
(d) 20°C and 1 kg/cm2
(e) none of the above.
Ans: b
68. The volumetirc efficiency of a compressor is
calculated on the basis of
(a) volume of air inhaled at working conditions
(b) volume of air inhaled at N.T.P. conditions
(c) volume at 0°C and 1 kg/cm2
(d) volume at 20°C and 1 kg/cm2
(e) none of the above.
Ans: b
69. The volumetric efficiency of a compressor falls
roughly as follows for every 100 m increase in
elevation
(a) 0.1%
(b) 0.5%
(c) 1.0%
(d) 5%
(e) 10%.
Ans: c
70. 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
semirotary type
(c) disc or feather type
(d) any of the above
(e) none of the above.
Ans: c
71. 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
(e) none of the above.
Ans: a
72. More than one stage will be preferred for
reciprocating compressor if the delivery pressure is
more than
(a) 2 kg/cm2
(b) 6 kg/cm2
(c) 10 kg/cm2
(d) 14.7 kg/cm2
(e) none of the above.
Ans: a
73. The advantage of multistage compression over
single stage compression is
(a) lower power consumption per unit of air
delivered
(b) higher volumetric efficiency
(c) decreased discharge temperature
(d) moisture free air
(e) all of the above.
Ans: e
74. 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
(e) more uniform torque, light cylinder and saving in
work.
Ans: b
75. As the value of index '«' is decreased, the
volumetric efficiency will
(a) increase
(b) decrease
(c) remain unaffected
(d) may increase/decrease depending on
compressor clearance
(e) none of the above.
Ans: b
76. 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) blade effectiveness
Ans: a
79. Losses in a centrifugal compressor are due to
(a) inlet losses
(b) impeller channel losses
(c) diffuser losses
(d) all of the above
(e) none of the above
Ans: d
80. The volumetric efficiency of a compressor falls
roughly as follows for every 5°C increase in
atmospheric temperature
(a) 0.1%
(b) 0.5%
(c) 1%
(d) 5%
(e ) 10%.
Ans: c
81. The indicated work per unit mass of air
delivered is
(a) directly proportional to clearance volume
(b) greatly affected by clearance volume
(c) not affected by clearance volume
(d) inversely proportional to clearance volume
Ans: c
89. For actual single stage centrifugal compressor,
the maximum pressure ratio is of the order of
(a) 1 : 1.2
(b) 1 : 2
(c) 1 : 4
(d) 1 : 10
(e) 1 : 1
Ans:
90. Which is false statement about advantages of
multistage compressor in comparison to single
stage compressor
(a) less power requirement
(b) better mechanical balance
(c) less loss of air due to leakage past the cylinder
(d) more effective lubrication
(e) lower volumetric efficiency.
Ans: e
91. The ratio of isentropic work to Euler work is
known as
(a) pressure coefficient
(b) work coefficient
(c) polytropic reaction
(d) slip factor
(e) compressor efficiency.
Ans: a
92. The criterion of the thermodynamic efficiency for
rotary compressor is
(a) isentropic compression
(b) isothermal compression
(c) polytropic compression
(d) any one of the above
(e) none of the above.
Ans: a
93. For supplying intermittent small quantity of air at
high pressure, following compressor is best suited
(a) centrifugal
(b) reciprocating
(c) axial
(d) screw
(e) turbo jet.
Ans: b
94. For minimum work in multistage compression,
assuming same index of compression in all stages
(a) work done in first stage should be more
(b) work done in subsequent stages should
increase
(c) work done in subsequent stages should
decrease
(d) work done in all stages should be equal
(e) work done in any stage is no criterion for
minimum work but depends on other factors.
Ans: d
95. 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
(e) unpredictable.
Ans: a
96. Diffuser in a compressor is used to
(a) increase velocity
(b) make the flow stream-line
(c) convert pressure energy into kinetic energy
(d) convert kinetic energy into pressure energy
(e) increase degree of reaction.
Ans: d
98. The ratio of isentropic work to euler's work is
known as
(a) compressor efficiency
(b) isentropic efficiency
(c) Euler's efficiency
(d) pressure coefficient
(e) pressure ratio.
Ans: d
99. The thermodynamic efficiency of rotary
compressor is based on
(a) isothermal compression
(b) adiabatic compression
(c) isentropic compression
(d) polytropic compression
(e) none of the above.
Ans: b
100. Phenomenon of choking in compressor means
(a) no flow of air
(b) fixed mass flow rate regardless of pressure
ratio
(c) reducing mass flow rate with increase in
pressure ratio
(d) increased inclination of chord with air steam
(e) does not occur.
Ans: b
101. The maximum compression ratio in an actual
single stage axial flow comperssor is of the order of
(a) 1 : 1.2
(b) 1 : 2
(c) 1 : 5
(d) 1 : 10
(e) 1 : 1
Ans: a
102. Maximum delivery pressure is a rotary air
compressor is of the order of
(a) 6 kg/cm2
(b) 10 kg/cm2
(c) 16 kg/cm2
(d) 25 kg/cm2
(e) 40 kg/cm2.
Ans: b
103. Surging 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
(e) production of no air pressure.
Ans: c
104. Pick up wrong statement.
Surging phenomenon in centrifugal com-pressor
depends on
(a) mass flow rate
(b) pressure ratio
(c) change in load
(d) stagnation pressure at the outlet
(e) all of the above.
Ans: d
105. The ratio of the increase in pressure in rotor
blades to total increase in pressure in the stage is
called
(a) pressure ratio
(b) pressure coefficient
(c) degree of reaction
(d) slip factor
(e) stage factor.
Ans: c
106. Axial flow compressor resembles
(a) centrifugal pump
(b) reciprocating pump
(c) turbine
(d) sliding vane compressor
(e) none of the above.
Ans: c
107. Axial flow compressor has the following
advantage over centrifugal compressor
(a) larger air handling ability per unit frontal area
(b) higher pressure ratio per stage
(c) aerofoil blades are used
(d) higher average velocities
(e) none of the above.
Ans: a
108. Actual compression curve is
(a) same as isothermal
(b) same as adiabatic
(c) better than isothermal and adiabatic
(d) in between isothermal and adiabatic
(e) none of the above.
Ans: d
109. Atmospheric pressure is 1.03 kg/cm and
vapour pressure is 0.03 kg/cm . The air pressure
will be
(a) 1.03 kg/cm2
(b) 1.06 kg/cm2
(c) 1.00 kg/cm2
(d) 0.53 kg/cm2
(e) 0.5 kg/cm2.
Ans: c
110. The pressure ratio of an ideal vaned
compressor with increase in mass flow rate
(a) increases
(b) decreases
(c) remains constant
(d) first decreases and then increases
(e) unpredictable.
Ans: c
111. Rotary compressors are suitable for
(a) large discharge at high pressure
(b) low discharge at high pressure
(c) large discharge at low pressure
(d) low discharge at low pressure
(e) there is no such limitation.
Ans: c
112. The vloumetric efficiency of compressor with
increase in compression ratio will
(a) increase
(b) decrease
(c) remain same
(d) may increase/decrease depending on clearance
volume
(e) none of the above.
Ans: b
113. 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
(e) production of no air pressure.
Ans: d
114. Pick up the wrong statement
(a) centrifugal compressors deliver prac-tically
constant pressure over a considerable range of
capacities
(b) Axial flow compressors have a sub-stantially
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
(e) axial flow compressors apt to be longer as
compared to centrifugal type.
Ans: d
115. The work ratio of a gas turbine plant is defined
as the ratio of
(a) net work output and heat supplied (6) net work
output and work done by tur¬bine
(c) actual heat drop and isentropic heat drop
(d) net work output and isentropic heat drop
(e) isentropic increase/drop in tempera¬ture and
actual increase/ drop in temperature.
Ans: b
116. Gas turbine works on
(a) Brayton or Atkinson cycle
(b) Carnot cycle
(c) Rankine cycle
(d) Erricsson cycle
(e) Joule cycle.
Ans: a
117. The work ratio of simple gas turbine cycle
depends on
(a) pressure ratio
(b) maximum cycle temperature
(c) minimum cycle temperature
(d) all of the above
(e) none of die above.
Ans: d
118. 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
(e) unpredictable.
Ans: a
119. Open cycle gas turbine works on
(a) Brayton or Atkinson cycle
(6) Rankine cycle
(c) Carnot cycle
(d) Erricsson cycle
(e) Joule cycle.
Ans: a
120. The fuel consumption in gas turbines is
accounted for by
(a) low.er heating value
(b) higher heating value
(c) heating value
(d) higher calorific value
(e) highest calorific value.
Ans: a
121. Gas turbines for power generaion 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
(e) when other sources of power fail.
Ans: b
122. Mechanical efficiency of gas turbines as
compared to I.C engines is
(a) higher
(b) lower
(c) same
(d) depends on on odier considerations
(e) unpredictable.
Ans: a
123. The ratio of specific weighf/h.p. of gas turbin
and I.C engines may be typically of the order of
(a) 1 : 1
(b) 2 : 1
(c) 4 : 1
(d) 1:2
(e) 1 : 6.
Ans: e
124. 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
(e) unpredictably.
Ans: c
125. The air-fuel ratio in gas turbines is of the order
of
(a) 7 : 1
(b) 15 : 1
(c) 30 : 1
(d) 40 : 1
(e) 50: 1.
Ans: e
126. The pressure ratio in gas turbines is of the
order of
(a),2:l
(b)4:1
(c) 61: 1
(d) 9 : 1
(e) 12:1.
Ans: c
128. The hottest point in a gas turbine is
(a) at the base
(b) at the tip
(c) in the center
(d) between ~ to i of the blade height
(e) uniformly heated.
Ans: d
129. 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
(e) part of exhaust gases are heated and mixed up
with atmospheric air to utilise exhaust heat.
Ans: b
130. 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
(e) none of the above.
Ans: b
131. Efficiency of gas turbine is increased by
(a) reheating
(b) inter cooling
(c) adding a regenerator
(d) all of the above
(e) none of the above.
Ans: c
132. Temperature of gases at end of compression
as compared to exhaust gases in a gas turbine is
(a) higher
(b) lower
(c) equal
(d) can't be compared
(e) unpredictable.
Ans: b
133. The ideal efficiency of simple gas turbine cycle
depends on
(a) pressure ratio
(b) maximum cycle temperature
(c) minimum cycle temperature
(d) all of the above
(e) none of the above.
Ans: a
134. The thermal efficiency of a simple gas turbine
for a given turbine inlet temperature with increase
in pressure ratio
(a) increases
(b) decreases
(c) first increases and then decreases
(d) first decreases and then increases
(e) remains same.
Ans: a
135. Gas turbines use following type of air
compressor
(a) centrifugal type
(b) reciprocating type
(c) lobe type
(d) axial flow type
(e) none of the above.
Ans: d
136. As the turbine inlet temperature increases, the
thermal efficiency of gas turbine for the optimum
pressure ratio
(a) increases
(b) decreases
(c) remains same
(d) first increases and then decreases
(e) first decreases and then increases.
Ans: a
137. There is a certain pressure ratio (optimum) for
a gas turbine at which its thermal efficiency is
maximum. With increase in turbine temperature, the
value of pressure ratio for the peak efficiency would
(a) remain same
(b) decrease
(c) increase
(d) unpredictable
(e) none of the above.
Ans: c
138. The material commonly used for air craft gas
turbine is
(a) stainless steel
(b) high alloy' steel
(c) duralumin
(d) Timken, Haste and Inconel allpys
(e) titanium.
Ans: d
139. It is not possible to use closed gas turbine
cycle in aeronautical engines because
(a) it is inefficient
(b) it is bulky
(c) it requires cooling water for its operation
Ans: c
140. The combustion efficiency of a gas turbine
using perfect combustion chamber is of the order of
(a) 50%
(b) 75%
(c) 85%
(d) 90%
(e ) 99%.
Ans: e
141. The jnaximum combustion pressure in gas
turbine as compared to I.C. engine is
(a) more
(b) less
(c) same
(d) depends on other factors
(e) unpredictable.
Ans: b
142. For an irreversible gas turbine cycle, the
efficiency and work ratio both depend on
(a) pressure ratio alone
(b) maximum cycle temperature alone
(c) minimum cycle temperature alone
(d) both pressure ratio and maximum cycle
temperature
(e) none of the above.
Ans: d
143. Producer gas is produced by
(a) carbonisation of coal
(b) passing steam over incandescent coke
(c) passing air and a large amount of steam over
waste coal at about 65°C
(d) partial combustion of coal, coke, anthracite coal
or charcoal in a mixed air steam blast
(e) same way as the natural gas.
Ans: d
144. Water gas is produced by
(a) carbonisation of coal
(b) passing steam over incandescent coke
(c) passing air and a large amount of steam over
waste coal at about 65°C
(d) partial combustion of caol, eke, anthractie coal
or charcoal in a mixed air steam blast
(e) same way as the natural gas.
Ans: b
14 Water is injected in gas turbine cycle to
(a) control temperature
(b) control output of turbine
(c) control fire hazards
(d) increase efficiency
(e) it is never done.
Ans: b
146. A gas turbine used in air craft should have
(a) high h.p. and low weight
(b) low weight and small frontal area
(c) small frontal area and high h.p.
(d) high speed and high h.p.
(e) all of the above.
Ans: b
148. 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
(e) none of the above.
Ans: a
149. 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 tempeature drop to the
isentrpic total head drop from total head inlet to
static head outlet
(d) actual compressor work and theoretical
comprssor work
(e) none of the above.
Ans: c
150. The degree of reaction of an axial flow turbine
is the ratio of isentropic temperature drop in a blade
row to the
(a) adiabatic temperature drop in the stage
(b) total temperature drop
(c) total temperature drop in the stage
(d) total adiabaitc temperature drop
(e) difference of maximum and minimum
temperature in the cycle.
Ans: c
153. 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
(e) isobaric.
Ans: a
154. Pick up the correct statement
(a) gas turbine uses low air-fuel ratio to economise
on fuel
(b) gas turhine 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
(e) none of the above.
Ans: b
15 Intercooling in gas turbine results in
(a) increase in net output but decrease in thermal
efficiency
(b) increase in thermal efficiency but decrease
in net output
(c) increase in both thermal efficiency and net
output
(d) decrease in both thermal efficiency and net
output
(e) none of the above.
Ans: a
156. 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)Vi=V0
(b)Vt>V0
(c) U,<V0
(d)V,= U0
(e) Vri=Vm.
Ans: a
157. Pick up the wrong statement
(a) large gas turbines employ axial flow
compressors
(b) axial flow compressors are more stable than
centrifugal type compressors but not as efficient
(c) axial flow compressors have high capacity and
efficiency
(d) axial flow compressors have instability
region of operation
(e) centrifugal compressors are used mainly on low
flow pressure ratio gas turbines.
Ans: b
158. The power available for take off and climb in
case of turbojet engine as compared to
reciprocating engine is
(a) less
(b) more
(c) same
(d) may be less or more depending on ambient
conditons
(e) unpredictable.
Ans: a
159. Pick up the correct statement
(a) large gas turbines use radial inflow turbines
(b) gas turbines have their blades similar to steam
turbine
(c) gas .turbine's blade will appear as impulse
section at the hub and as a reaction section at tip
(d) gas turbines use both air and liquid cooling
(e) all of the above are correct.
Ans: c
160. A closed gas turbine in which fuel is burnt
directly in the air is not possible because of
(a) high pressure ratio
(b) increasing gas temperature
(c) high specific volume
(d) high friction losses
(e) paucity of 02.
Ans: e
