Top Most Compressors Objective Questions
1.1 m of air at atmospheric condition weighs approximately
0.5 kg
1.0 kg
1.3 kg
2.2 kg
3.2 kg.
ANSWER : : 1.3 kg
2.What will be the volume of air at 327�C if its volume at 27�C is 1.5 m3/mt
3 m3/mt .
1.5 m3/mt
18 m3/mt’
6 m3/mt
0.75 m3/mt.
ANSWER : : 3 m3/mt .
3.Aeroplanes employ following type of compressor
radial flow
axial flow
centrifugal
combination of above
none of the above.
ANSWER : : axial flow
4.Clearance volume in actual reciprocating compressors is essential
to accommodate Valves in the cylinder head
to provide cushioning effect
to attain high volumetric efficiency
to avoid mechanical bang of piston with cylinder head
to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.
ANSWER : : to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.
5.Standard air is the air at
atmospheric conditions at any specific location
20�C and 1 kg/cm2 and relative humidity 36%
0�C and standard atmospheric conditions
15�C and 1 kg/cm2
25�C, 1 kg/cm2 and RH of 60%.
ANSWER : : 20�C and 1 kg/cm2 and relative humidity 36%
6.The- most efficient method of compressing air is to compress it
isothermally
adiabatically
isentropically
isochronically
as per law pV
ANSWER : : isothermally
7.Ratio of indicated H.P. and brake H.P. is known as
mechanical efficiency
volumetric efficiency
isothermal efficiency
adiabatic efficiency
relative efficiency.
ANSWER : : mechanical efficiency
8.An ideal air compressor cycle with clearance on p-v diagram can be represented by following processes
one adiabatic, two isobaric, and one constant volume
two adiabatic and two isobaric
two adiabatic, one isobaric and one constant volume,
one adiabatic, one isobaric and two constant volume
two isobaric, two adiabatic and one constant volume.
ANSWER : : two adiabatic and two isobaric
9.The overall isothermal eiffciency of compressor is defined as the ratio of
isothermal h.p. to the BHP of motor
isothermal h.p. to adiabatic h.p.
power to drive compressor to isothermal h.p.
work to compress air isothermally to work for actual compression
isothermal work to ideal work.
ANSWER : : isothermal h.p. to the BHP of motor
10.Compression efficiency is compared against
ideal compression
adiabatic compression
botii isothermal and adiabatic compression
isentropic compression
isothermal compression.
ANSWER : : isothermal compression.
11.The work done per unit mass of air in compression will’be least when n is equal to
1
1.2 ,
1.3
1.4
1.5
ANSWER : : 1
12.Adiabatic compression is one in which
temperature during compression remains constant
no heat leaves or enters the compressor cylinder during compression
temperature rise follows a linear relationship
work done is maximum
entropy decreases.
ANSWER : : no heat leaves or enters the compressor cylinder during compression
13.Cylinder clearance in a compressor should be
as large as possible
as small as possible
about 50% of swept volume
about 100% of swept volume
none of the above.
ANSWER : : as small as possible
14.The ratio of work done per cycle to the swept volume in case of compressor is called
compression index
compression ratio
compressor efficiency
mean effective pressure
compressor effectiveness.
ANSWER : : mean effective pressure
15.Inter cooling in compressors
cools the delivered air
results in saving of power in compressing a given volume to given pressure
is the standard practice for big compressors
enables compression in two stages
prevents compressor jacket running very hot.
ANSWER : : results in saving of power in compressing a given volume to given pressure
16.An ideal air compressor cycle without clearance on p-v diagram can be represented by following processes
one adiabatic, two isobaric, and one constant volume
two adiabatic and two isobaric
two adiabatic, one isobaric and one constant volume
one adiabatic, one isobaric and two constant volume
two isobaric, two adiabatic and one constant volume.
ANSWER : : one adiabatic, two isobaric, and one constant volume
17.Isothermal compression efficiency, even when running at high speed, can be approached by using
multi-stage compression
cold water spray
both (a) and (b) above
fully insulating the cylinder
high stroke.
ANSWER : : both (a) and (b) above
18.Isothermal compression efficiency can be attained by running the compressor
at very high speed
at very slow speed
at average speed
at zero speed
isothermally.
ANSWER : : at very slow speed
19.The pressure and temperature conditions of air at the suction of compressor are
atmospheric
slightly more than atmospheric
slightly less than atmospheric
pressure slightly more than atmospheric and temperature slightly less than atmospheric
pressure sightly less than atmospheric and temperature slightly more than atmospheric.
ANSWER : : pressure sightly less than atmospheric and temperature slightly more than atmospheric.
20.Isothermal compression though most efficient, but is not -practicable because
it requires very big cylinder
it does not increase pressure much
it is impossible in practice
compressor has to run at very slow speed to achieve it
it requires cylinder to be placed in water.
ANSWER : : compressor has to run at very slow speed to achieve it
21.Maximum work is done in compressing air when the compression is
isothermal
adiabatic
polytropic
any one of the above
none of the above.
ANSWER : : adiabatic
22.The capacity of a compressor is 5 m /mih. 5 m /min refers to
standard air
free air
compressed air
compressed air at delivery pressure
air sucked.
ANSWER : : free air
23.The compressor capacity with decrease in suction temperature
increases
decreases
remains unaffected
may increase or decrease depending on compressor capacity
increases upto certain limit and then decreases.
ANSWER : : increases
24.Ratio of compression is the ratio of
gauge discharge pressure to the gauge intake pressure
absolute discharge pressure to the ab-solute intake pressure
pressures at discharge and suction cor-responding to same temperature
stroke volume and clearance volume
none of the above.
ANSWER : : absolute discharge pressure to the ab-solute intake pressure
25.Volumetric efficiency is
the ratio of stroke volume to clearance volume
the ratio of the air actually delivered to the amount of piston displacement
reciprocal of compression ratio
index of compressor performance
proportional to compression ratio.
ANSWER : : the ratio of the air actually delivered to the amount of piston displacement
26.To avoid moisture troubles, the branch connections from compressed air lines should be taken from
top side of main
bottom side of main
left side of main
right side of main
any location.
ANSWER : : top side of main
27.After-cooler is used to
cool the air
decrease the delivery temperature for ease in handling
cause moisture and oil vapour to drop out
reduce volume
increase pressure.
ANSWER : : cause moisture and oil vapour to drop out
28.Which is false statement about multistage compression .
Power consumption per unit of air delivered is low
Volumetric efficiency is high
It is best suited for compression ratios around 7:1
The moisture in air is condensed in the intercooler
Outlet temperature is reduced.
ANSWER : : Volumetric efficiency is high
29.Ratio of indicated h.p. to shaft h.p. in known as
compressor efficiency
isothermal efficiency
volumetric efficiency
mechanical efficiency
adiabatic efficiency.
ANSWER : : mechanical efficiency
30.In multistage compressor, the isothermal compression is achieved by
employing intercooler
by constantly cooling the cylinder
by running compressor at very slow speed
by insulating the cylinder
none of the above.
ANSWER : : by running compressor at very slow speed
31.Which is false statement about air receivers
These are used to dampen pulsations ,
These act as reservoir to- take care of sudden demands
These increase compressor efficiency
These knock out some oil and moisture
These reduce frequent on/off operation of compressors.
ANSWER : : These increase compressor efficiency
32.A compressor at high altitude will draw
more power
less power
same power
more/less power depending on other factors
none of the above.
ANSWER : : less power
33.Volumetric efficiency of air compressors is of the order of
20-30%
40-50%
60-70%
70-90%
90-100%.
ANSWER : : 70-90%
34.The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is
less
more
same
more/less depending on compressor capacity
unpredictable.
ANSWER : : more
35.An air compressor may be controlled by
throttle control (b) clearance control
blow-off control
any one of the above
none of the above.
opt 5
ANSWER : : any one of the above
36.Rotary compressor is best suited for
large quantity of air at high pressure
small quantity of air at high pressure
small quantity of air at low pressure
large quantity of air at low pressure
any one of the above.
ANSWER : : small quantity of air at high pressure
37.Reciprocating air compressor is best suited for
large quantity of air at high pressure
small quantity of air at high pressure
small quantity of air at low pressure
large quantity of air at low pressure
any one of the above.
ANSWER : : large quantity of air at high pressure
38.Euler’s equation is applicable for
centrifugal compressor
axial compressor
pumps
all of the above
none of the above.
ANSWER : : all of the above
39.Volumetric efficiency of a compressor without clearance volume
increases with increase in compression ratio
decreases with increase in compression ratio
is not dependent upon compressin ratio
may increase/decrease depending on compressor capacity
unpredictable.
ANSWER : : is not dependent upon compressin ratio
40.The thrust on the rotor in a centrifugal compressor is produced by
radial component
axial component
tangential component
resultant component
opt 5
ANSWER : s: b
41.Out of the following, from where you will prefer to take intake for air compressor
from an air conditioned room maintained at 20�C
from outside atmosphere at 1�C
from coal yard side
from a side where cooling tower is located nearby
from any one of the above locations.
ANSWER : : from a side where cooling tower is located nearby
42.The compressor performance at higher altitude compared to sea level will be
same
higher
lower
dependent on other factors
none of the above.
ANSWER : : lower
43.To aviod moisture troubles, the compressed air main line should
rise gradually towards the point of use
drop gradually towards the point of use
be laid vertically
be laid exactly horizontally
none of the above
ANSWER : : drop gradually towards the point of use
44.Volumetric efficiency of a compressor with clearance volume
increases with increase in compression ratio
decreases with increase in compression ratio
in not dependent upon compression ratio
may increase/decrease depending on compressor capacity
unpredictable.
ANSWER : : decreases with increase in compression ratio
45.The compressor efficiency is the
isothermal H.P/indicated H.R
isothermal H.P./shaft H.R
total output/air input
compression work/motor input
none Of the above.
ANSWER : : isothermal H.P/indicated H.R
46.Separators in compressor installations are located
before intercooler
after intercooler
after receiver
between after-cooler and air receiver
before suction.
ANSWER : : between after-cooler and air receiver
47.The capacity of compressor will be highest when its intake temperature is
lowest
highest
anything.
atmospheric
none of the above.
ANSWER : : atmospheric
48.Mining industry usually employs following motive power
A.C. electric motor
compressed air
petrol engine
diesel engine
D.C. electric motor.
ANSWER : : compressed air
49.The clearance volume of the air compressor is kept minimum because
it allows maximum compression to be achieved
it greatly affects volumetric efficiency
it results in minimum work
it permits isothermal compression
none of the above.
ANSWER : : it greatly affects volumetric efficiency
50.Pick up the wrong statement about advantages of multistage compression
better lubrication is possible advantages of multistage
more loss of air due to leakage past the cylinder
mechanical balance is better
air can be cooled perfectly in between
more uniform torque, light cylinder and saving in work.
ANSWER : : more loss of air due to leakage past the cylinder
51.For a compressor, least work will be done if the compression is
is entropic
isothermal
poly tropic
somewhere in between is entropic and isothermal
none of the above.
ANSWER : : isothermal
52.For slow-speed large capacity compressor, following type of valve will be best suited
poppet valve
mechanical valve of the corliss, sleeve, rotary or semirotary type
disc or feather type
any of the above
none of the above.
ANSWER : : disc or feather type
53.More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than
2 kg/cm2
6 kg/cm2
10 kg/cm2
14.7 kg/cm2
none of the above.
ANSWER : : 2 kg/cm2
54.The ratio of isentropic work to Euler work is known as
pressure coefficient
work coefficient
polytropic reaction
slip factor
compressor efficiency.
ANSWER : : pressure coefficient
55.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
increase
decrease
remain unaffected
other factors control it
unpredictable.
ANSWER : : increase
56.During base load operation, the best method of controlling compressor is
start-stop motor
constant speed unloaded
relief valve
variable speed
none of the above.
ANSWER : : start-stop motor
57.For supplying intermittent small quantity of air at high pressure, following compressor is best suited
centrifugal
reciprocating
axial
screw
turbo jet.
ANSWER : : reciprocating
58.The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called
slip factor
velocity factor
velocity coefficient
blade effectiveness
opt 5
ANSWER : : slip factor
59.The ratio of isentropic work to euler’s work is known as
compressor efficiency
isentropic efficiency
Euler’s efficiency
pressure coefficient
pressure ratio.
ANSWER : : pressure coefficient
60.The volumetric efficiency of a compressor is calculated on the basis of
volume of air inhaled at working conditions
volume of air inhaled at N.T.P. conditions
volume at 0�C and 1 kg/cm2
volume at 20�C and 1 kg/cm2
none of the above.
ANSWER : : volume of air inhaled at N.T.P. conditions
61.Diffuser in a compressor is used to
increase velocity
make the flow stream-line
convert pressure energy into kinetic energy
convert kinetic energy into pressure energy
increase degree of reaction.
ANSWER : : convert kinetic energy into pressure energy
62.The indicated work per unit mass of air delivered is
directly proportional to clearance volume
greatly affected by clearance volume
not affected by clearance volume
inversely proportional to clearance volume
opt 5
ANSWER : : not affected by clearance volume
63.The volumetric efficiency of a compressor falls roughly as follows for every 100 m increase in elevation
0.1%
0.5%
1.0%
5%
10%.
ANSWER : : 1.0%
64.In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to
N.T.P. conditions
intake temperature and pressure conditions
0�C and 1 kg/cm2
20�C and 1 kg/cm2
none of the above.
ANSWER : : intake temperature and pressure conditions
65.The criterion of the thermodynamic efficiency for rotary compressor is
isentropic compression
isothermal compression
polytropic compression
any one of the above
none of the above.
ANSWER : : isentropic compression
66.As the value of index ‘�’ is decreased, the volumetric efficiency will
increase
decrease
remain unaffected
may increase/decrease depending on compressor clearance
none of the above.
ANSWER : : decrease
67.For minimum work in multistage compression, assuming same index of compression in all stages
work done in first stage should be more
work done in subsequent stages should increase
work done in subsequent stages should decrease
work done in all stages should be equal
work done in any stage is no criterion for minimum work but depends on other factors.
ANSWER : : work done in all stages should be equal
68.The volumetric efficiency of a compressor falls roughly as follows for every 5�C increase in atmospheric temperature
0.1%
0.5%
1%
5%
opt 5
ANSWER : ) 10%.
69.Losses in a centrifugal compressor are due to
inlet losses
impeller channel losses
diffuser losses
all of the above
none of the above
ANSWER : : all of the above
70.The thermodynamic efficiency of rotary compressor is based on
isothermal compression
adiabatic compression
isentropic compression
polytropic compression
none of the above.
ANSWER : : adiabatic compression
71.Which is false statement about advantages of multistage compressor in comparison to single stage compressor
less power requirement
better mechanical balance
less loss of air due to leakage past the cylinder
more effective lubrication
lower volumetric efficiency.
ANSWER : : lower volumetric efficiency.
72.The advantage of multistage compression over single stage compression is
lower power consumption per unit of air delivered
higher volumetric efficiency
decreased discharge temperature
moisture free air
all of the above.
ANSWER : : all of the above.
73.A centrifugal compressor works on the principle of
conversion of pressure energy into kinetic energy
conversion of kinetic energy into pres�sure energy
centripetal action
generating pressure directly
combination of (a) and (d).
ANSWER : : conversion of kinetic energy into pres�sure energy
74.The fuel consumption in gas turbines is accounted for by
low.er heating value
higher heating value
heating value
higher calorific value
highest calorific value.
ANSWER : : low.er heating value
74.Gas turbines for power generation are normally used
to supply base load requirements
to supply peak load requirements
to enable start thermal power plant
in emergency
when other sources of power fail.
ANSWER : : to supply peak load requirements
75.Mechanical efficiency of gas turbines as compared to I.C engines is
higher
lower
same
depends on osier considerations
unpredictable.
ANSWER : : higher
76.Axial flow compressor has the following advantage over centrifugal compressor
larger air handling ability per unit frontal area
higher pressure ratio per stage
aerofoil blades are used
higher average velocities
none of the above.
ANSWER : : larger air handling ability per unit frontal area
77.The volumetric efficiency of compressor with increase in compression ratio will
increase
decrease
remain same
may increase/decrease depending on clearance volume
none of the above.
ANSWER : : decrease
78.Open cycle gas turbine works on
Brayton or Atkinson cycle
ankine cycle
Carnot cycle
Erricsson cycle
Joule cycle.
ANSWER : : Brayton or Atkinson cycle
79.Stalling of blades in axial flow compressor is the phenomenon of
air stream blocking the passage
motion of air at sonic velocity
unsteady periodic and reversed flow
air stream not able to follow the blade contour
production of no air pressure.
ANSWER : : air stream not able to follow the blade contour
80.Atmospheric pressure is 1.03 kg/cm and vapor pressure is 0.03 kg/cm . The air pressure will be
1.03 kg/cm2
1.06 kg/cm2
1.00 kg/cm2
0.53 kg/cm2
0.5 kg/cm2.
ANSWER : : 1.00 kg/cm2
81.The ratio of the increase in pressure in rotor blades to total increase in pressure in the stage is called
pressure ratio
pressure coefficient
degree of reaction
slip factor
stage factor.
ANSWER : : degree of reaction
82.Rotary compressors are suitable for
large discharge at high pressure
low discharge at high pressure
large discharge at low pressure
low discharge at low pressure
there is no such limitation.
ANSWER : : large discharge at low pressure
83.Maximum delivery pressure is a rotary air compressor is of the order of
6 kg/cm2
10 kg/cm2
16 kg/cm2
25 kg/cm2
40 kg/cm2.
ANSWER : : 10 kg/cm2
84.The pressure ratio of an ideal vaned compressor with increase in mass flow rate
increases
decreases
remains constant
first decreases and then increases
unpredictable.
ANSWER : : remains constant
85.Gas turbine works on
Brayton or Atkinson cycle
Carnot cycle
Rankine cycle
Erricsson cycle
Joule cycle.
ANSWER : s: a
86.The maximum compression ratio in an actual single stage axial flow compressor is of the order of
1 : 1.2
1 : 2
1 : 5
1 : 10
1 : 1
ANSWER : : 1 : 1.2
87.Surging is the phenomenon of
air stream blocking the passage
motion of air at sonic velocity
unsteady, periodic and reversed flow
air stream not able to follow the blade contour
production of no air pressure.
ANSWER : : unsteady, periodic and reversed flow
88.Actual compression curve is
same as isothermal
same as adiabatic
better than isothermal and adiabatic
in between isothermal and adiabatic
none of the above.
ANSWER : : in between isothermal and adiabatic
89.The pressure ratio for an open cycle gas turbine compared to closed cycle gas turbine of same h.p. is
low
high
same
low/high depending on make and type
unpredictable.
ANSWER : : low
90.Axial flow compressor resembles
centrifugal pump
reciprocating pump
turbine
sliding vane compressor
none of the above.
ANSWER : : turbine
91.The pressure ratio in gas turbines is of the order of
,2:l
4:1
61: 1
9 : 1
12:1.
ANSWER : : 61: 1
92.The thermal efficiency of a gas turbine as compared to a diesel plant is
same
more
less
depends on other factors
unpredictably.
ANSWER : : less
93.The work ratio of simple gas turbine cycle depends on
pressure ratio
maximum cycle temperature
minimum cycle temperature
all of the above
none of die above.
ANSWER : : all of the above
94.Pick up the wrong statement
centrifugal compressors deliver prac-tically constant pressure over a con-> siderable range of capacities
Axial flow compressors have a sub-stantially constant delivery at variable pressures
centrifugal compressors have a wider stable operating range than axial flow compressors
axial flow compressors are bigger in diameter compared to centrifugal type
axial flow compressors apt to be longer as compared to centrifugal type.
ANSWER : : axial flow compressors are bigger in diameter compared to centrifugal type
95.Pick up wrong statement. Surging phenomenon in centrifugal compressor depends on
mass flow rate
pressure ratio
change in load
stagnation pressure at the outlet
all of the above.
ANSWER : : stagnation pressure at the outlet
96.The air-fuel ratio in gas turbines is of the order of
7 : 1
15 : 1
30 : 1
40 : 1
50: 1.
ANSWER : : 50: 1.
97.The ratio of specific weigh/h.p. of gas turbine and I.C engines may be typically of the order of
1 : 1
2 : 1
4 : 1
1:2
1 : 6.
ANSWER : : 1 : 6.
98.As the turbine inlet temperature increases, the thermal efficiency of gas turbine for the optimum pressure ratio
increases
decreases
remains same
first increases and then decreases
first decreases and then increases.
ANSWER : : increases
99.Efficiency of gas turbine is increased by
reheating
inter cooling
adding a re generator
all of the above
none of the above.
ANSWER : : adding a re generator
100.The thermal efficiency of a simple gas turbine for a given turbine inlet temperature with increase in pressure ratio
increases
decreases
first increases and then decreases
first decreases and then increases
remains same.
ANSWER : : increases
101.The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is
heated
compressed air before entering the combustion chamber is heated
bled gas from turbine is heated and readmitted for complete expansion
exhaust gases drive the compressor
part of exhaust gases are heated and mixed up with atmospheric air to utilize exhaust heat.
ANSWER : : compressed air before entering the combustion chamber is heated
102.The degree of reaction of an axial flow turbine is the ratio of is entropic temperature drop in a blade row to the
adiabatic temperature drop in the stage
total temperature drop
total temperature drop in the stage
total adiabatic temperature drop
difference of maximum and minimum temperature in the cycle.
ANSWER : : total temperature drop in the stage
103.Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is
higher
lower
equal
can’t be compared
unpredictable.
ANSWER : : lower
104.A gas turbine used in air craft should have
high h.p. and low weight
low weight and small frontal area
small frontal area and high h.p.
high speed and high h.p.
all of the above.
ANSWER : : low weight and small frontal area
105.The maximum combustion pressure in gas turbine as compared to I.C. engine is
more
less
same
depends on other factors
unpredictable.
ANSWER : : less
106.For an irreversible gas turbine cycle, the efficiency and work ratio both depend on
pressure ratio alone
maximum cycle temperature alone
minimum cycle temperature alone
both pressure ratio and maximum cycle temperature
none of the above.
ANSWER : : both pressure ratio and maximum cycle temperature
107.The ideal efficiency of simple gas turbine cycle depends on
pressure ratio
maximum cycle temperature
minimum cycle temperature
all of the above
none of the above.
ANSWER : : pressure ratio
108.If infinite number of heaters be used in a gas turbine, then expansion process in turbine approaches
isothermal
isentropic
adiabatic
isochoric
isobaric.
ANSWER : : isothermal
109.It is not possible to use closed gas turbine cycle in aeronautical engines because
it is inefficient
it is bulky
it requires cooling water for its operation
c
opt 5
ANSWER : The combustion efficiency of a gas turbine using perfect combustion chamber is of the order of
110.Pick up the correct statement
gas turbine uses low air-fuel ratio to economies on fuel
gas turbine uses high air-fuel ratio to reduce outgoing temperature
gas turbine uses low air-fuel ratio to develop the high thrust required
all of the above
none of the above.
ANSWER : : gas turbine uses high air-fuel ratio to reduce outgoing temperature
111.Producer gas is produced by
carbonation of coal
passing steam over incandescent coke
passing air and a large amount of steam over waste coal at about 65�C
partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
same way as the natural gas.
ANSWER : : partial combustion of coal, coke, anthracite coal or charcoal in a mixed air steam blast
112.In the axial flow gas turbine, the work ratio is the ratio of
compressor work and turbine work
output and input
actual total head temperature drop to the entropic total head drop from total head inlet to static head outlet
actual compressor work and theoretical compressor work
none of the above.
ANSWER : : actual total head temperature drop to the entropic total head drop from total head inlet to static head outlet
113.Gas turbines use following type of air compressor
centrifugal type
reciprocating type
lobe type
axial flow type
none of the above.
ANSWER : : axial flow type