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Mechanical Engineering
Engineering Thermodynamics
Quiz 13
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Q.1
Minimum work in compressor is possible when the value of adiabatic index ‘n’ is equal to
0.75
1
1.27
1.35
Q.2
Which of the following cycles has maximum efficiency?
Rankine
Stirling
Carnot
Brayton
Q.3
No liquid can exist as liquid at
Zero pressure
273°K
Vacuum
Centre of earth
Q.4
The molecular mass expressed in gram (i.e. 1 g - mole) of all gases, at N. T. P., occupies a volume of
0.224 liters
2.24 liters
22.4 liters
224 liters
Q.5
Otto cycle efficiency is higher than Diesel cycle efficiency for the same compression ratio and heat input because in Otto cycle
Heat rejection is lower
Expansion and compression are isentropic
Combustion is at constant volume
Maximum temperature is higher
Q.6
Which of the following processes is irreversible process?
Isothermal
Adiabatic
Throttling
All of the above
Q.7
The amount of heat required to raise the temperature of the unit mass of gas through one degree at constant volume, is called
Kilo Joule
Specific heat at constant volume
Specific heat at constant pressure
None of these
Q.8
A diathermic wall is one which
Prevents thermal interaction
Permits thermal interaction
Encourages thermal interaction
Discourages thermal interaction
Q.9
Rankine cycle efficiency of a good steam power plant may be in the range of
15 to 20%
35 to 45%
70 to 80%
90 to 95%
Q.10
The efficiency of an ideal Carnot engine depends on
a) working substance
b) on the temperature of the source only
c) on the temperature of the sink only
d) on the temperatures of both the source & the sink
Q.11
Which of the following contributes to the improvement of efficiency of Rankine cycle in a Thermal Power Plant?
reheating of steam at intermediate stage
regeneration use of steam for heating boiler feed water
use of high pressures
all of the mentioned
Q.12
A regenerative Rankine cycle may approach efficiency of a Carnot cycle between sametemperature by
a) reducing heat to condenser
b) reducing volume of steam passed into condenser
c) increasing turbine work
d) adding heat a highest temp.
Q.13
The temperature of feed water can be increased in following two ways in a regenerative Rankine cyclei) by passing feed water around turbine casing in direction opposite to flow of steamii) by bleeding certain portion of steam at the end of h.p expansion & mixing with condensate to make feed water at the temperature of boiler
a) i) is preferred over ii) for higher efficiency
b) ii) is preferred over i) for reduced moisture content of steam in l.p side
c) only i) is implemented in actual practice
d) by preferring ii) overi) significant gain in efficiency results
Q.14
The universal gas constant will be equal to difference between specific heats at constant pressure & constant volume for
1 kg mass of gas
1 molecule of gas
1 kg molecule of gas
any mass of gas
Q.15
Air expands from initial condition of pv1 to final condition of 1/2 p2v1.Choose the correct statement
a) no work is performed during expansion
b) expansion is isothermal
c) expansion is polytropic with n= 1.2
d) expansion is adiabatic
Q.16
Steam enters the turbine at 5.bar with dryness fraction of 0.9 & is expanded adiabatically to a pressure of 0.bar. It will enter the condenser with a quality very close to
a) 0.79
b) 0.815
c) 0.84
d) 0.86
Q.17
A power cycle using steam as working fluid consist ofi) constant pressure heat addition ii)adiabatic expansioniii) constant pressure heat rejection & iv) adiabatic compression. The cycle is
simple rankine cycle
modified rankine cycle
carnot cycle
regenerative rankine cycle
Q.18
Which of the following remains constant during an adiabatic expansion
a) entropy
b) temperature
c) internal energy
d) none of the above
Q.19
According to Carnot’s theorem, all heat engines operating between a given constant temperature source and sink, none has a higher efficiency than a reversible engine.
true
false
Q.20
Relative humidity is defined as
(saturation pressure of pure water) / pw
pw / (saturation pressure of pure water)
(saturation pressure of pure water) / p
p / (saturation pressure of pure water)
Q.21
The efficiency and work ratio of a simple gas turbine cycle are
low
very low
high
very high
Q.22
In a steam power plant which cycle requires two or more feed pumps
regenerative rankine cycle
reheat rankine cycle
simple rankine cycle
idealized regenerative rankine cycle
Q.23
The entropy __________ in an irreversible cyclic process.
remains constant
decreases
increases
Q.24
The optimum reheat pressure for most of the power plants is how many times of the initial steam pressure?
0.1-0.15
0.2-0.20
0.2-0.25
0.1-0.10
Q.25
Which of the following cycles is used in thermalpower plants?
a) brayton
b) carnot
c) ericsson
d) rankine
Q.26
By reducing the condenser pressure in Rankine power plant
a) heat supplied increases & work of cycle decreases
b) work of cycle & moisture content of steam in l.p side ofturbine increase
c) heat supplied & efficiency of cycle increase
d) work of cycle increases but heat supplied decreases
Q.27
Essential parts of a power plant operating on aRankine cycle are
a) engine or turbine
b) engine or turbine & conderser
c) engine or turbine, condenser, pump &boiler
d) engine or turbine & boiler
Q.28
Most of the fossil fuelbased power plants operate on
a) rankine cycle
b) brayton cycle
c) carnot cycle
d) either rankine or brayton cycle
Q.29
When unsaturated air flows over a sheet of water in an insulated chamber
specific humidity of air decreases
the water evaporates
both air and water are cooled during evaporation
all of the mentioned
Q.30
At any dbt, the the difference of wbt reading below below dbt, is the amount of water vapour held in mixture.
smaller, smaller
greater, greater
greater, smaller
smaller, greater
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