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DEPARTMENT OF MECHANICAL ENGINEERING
ME 6301- ENGINEERING THERMODYNAMICS
TWO MARKS QUESTION AND ANSWER
1
...

Ans: Thermal engineering is the science that deals with the energy transfer to practical
applications such as energy transfer power generation, refrigeration, gas compression and
its effect on the properties of working substance
...
What is meant by thermodynamic system? How do you classify it? (MU – Oct’99,
Apr’2000: BRU – Apr’96; MSU – Apr’96)
Ans: Thermodynamic system is defined as the any space or matter or group of matter
where the energy transfer or energy conversions are studied
...

(a) Open system
(b) Closed system
(c) Isolated system
3
...
(BNU – Nov’95)
Ans: When a system has only heat and work transfer, but there is no mass transfer, it is
called as closed system
...

4
...

Ans: When a system has both mass and energy transfer it is called as open system
...

5
...
(MU – Apr’98, MKU – Nov’95)
Closed System
1
...
Only heat and
work will transfer
...
System boundary is fixed one
3
...
Mass transfer will take place, in addition
to the heat and work transfer
...
System boundary may or may not
change
...
Air compressor, boiler

6
...
There is no heat, work and mass
transfer take place
...

Example: Entire Universe

7
...
(MU – Oct’99)
Ans: It isdefined as the amount of heat energy required to raise or lower the temperature
of unit mass of the substance through one degree when the pressure kept constant
...

8
...

Ans: it is defined as the amount of heat energy required to raise or lower the temperature
of unit mass of the substance through one degree when volume kept constant
...
What is meant by surroundings?
Ans: Any other matter out side the system boundary is called as surroundings
...
What is boundary?
Ans: System and surroundings are separated by an imaginary line is called boundary
...
What is meant by thermodynamic property? (MU – Apr’2001; BRU – Nov’96;
BNU – Nov’94)
Ans: Thermodynamic property is any characteristic of a substance which is used to
identify the state of the system and can be measured, when the system remains in an
equilibrium state
...
How do you classify the property?
Ans: Thermodynamic property can be classified into two types
...
Intensive or Intrinsic and
2
...

13
...
(MU – Oct’96,98; MKU – Apr’96)
Ans: The properties which are independent on the mass of the system is called intensive
properties
...
g
...
,
The properties which are dependent on the mass of the system is called extensive
properties
...
g
...

14
...
Independent on the mass of the system
Dependent on the mass of the system
...
If we consider part of the system these
If we consider part of the system it will
properties remain same
...

e
...
pressure, Temperature specific volume e
...
, Total energy, Total volume, weight
etc
...
,
3
...
What do you understand by equilibrium of a system?
Ans: When a system remains in equilibrium state, it should not undergo any charges to its
own accord
...
What is meant by thermodynamic equilibrium? (MU – Apr’98; MSU – Apr’96)
Ans: When a system is in thermodynamic equilibrium, it should satisfy the following
three conditions
...

17
...

18
...
It violates first
law of thermodynamics, It is impossible to construct an engine working with this
principle
...
Define the term process (MKU – Nov’96)
Ans: It is defined as the change of state undergone by a gas due to energy flow
...
Define the term Cycle: (MKU – Nov’96)
Ans: When a system undergoes a series of processes and return to its initial condition, it
is known as cycle
...
What is meant by open and closed cycle
...

In a open cycle, the same working substance will be exhausted to the surroundings after
expansion
...
What is meant by reversible and irreversible process
...
It is possible only when the system passes
through a continuous series of equilibrium state
...

23
...


Example: Pressure, volume, temperature, etc
...

Example: Heat transfer, work transfer
...
What is Quasi – Static process? (MU – Oct’98, Apr’2000 & 2001; BNU –
Nov’95)
Ans: The process is said to be quasi – static, it should proceed infinitesimally slow and
follows continuous series of equilibrium states
...

Therefore, the quasi static process may be an reversible process
...
Explain Zeroth Law of thermodynamics? (MU – Nov’94, Apr’2001; BRU –
Apr’96)
Ans: Zeroth law of thermodynamics states that when two systems are separately in
thermal equilibrium with a third system, then they themselves are in thermal equilibrium
with each other
...
Define the term enthalpy? (MU – Oct’99)
Ans: The Combination of internal energy and flow energy is known as enthalpy of the
system
...

Mathematically, enthalpy (H) = U + pv KJ)
Where, U – internal energy
p – pressure
v – volume
In terms of Cp & T → H = mCp (T2-T1)KJ
27
...

It is also defined as the energy possessed by a gas at a given temperature
...
What is meant by thermodynamic work?
Ans: It is the work done by the system when the energy transferred across the boundary
of the system
...

29
...

Ans: Heat is the energy crossing the boundary due to the temperature difference between
the system and surroundings
...
Give the general gas energy equations
...

31
...

32
...
(MU – Oct’2000; MKU – Nov’96; BRU –
Nov’95)
Ans: Entropy is an important thermodynamic property, which increases with addition of
heat and decreases with its removal
...
It is an
unavailability of energy during energy transfer
...
Define an isentropic process
...
It is a process
which follows the law of pVy = C is known as isentropic process
...

34
...

Ans: When a gas or vapour expands and flows through an aperture of small size, the
process is called as throttling process
...
Work done in a free expansion process is _________ (MU – Apr’97)
Ans: Zero
36
...

Ans: When a gas expands suddenly into a vacuum through a large orifice is known as
free expansion process
...
Which property is constant during throttling? (MU – Oct’98, Oct’2000)
Ans: Enthalpy
38
...
The polytropic index (n) is given by ________ (MU – Apr’95 & 96)
Ans: n = log (P2/P1)/ log (V1/V2)
40
...
MU –Nov’94)
Ans: Isothermal process
...
Write down the characteristic gas equation
...

42
...

43
...

In case of non – flow across the system and boundary
...
State the Kelvin – Plank statement of second law of thermodynamics
Ans: Kelvin – Plank states that it is impossible to construct a heat engine working on
cyclic process, whose only purpose is to convert all the heat energy given to it into an
equal amount of work
...
State Clausius statement of second law of thermodynamics
...

46
...

Ans: No heat engine operating in a cyclic process between two fixed temperature, can be
more efficient than a reversible engine operating between the same temperature limits
...
What are the Corollaries of Carnot theorem
...

(ii) The efficiency of any reversible heat engine operating between two reservoirs is
independent of the nature of the working fluid and depends only on the temperature of
the reservoirs
...
Define – PMM of second kind
...
Thus it gives 100% efficiency
...
What is the difference between a heat pump and a refrigerator?
Ans: Heat pump is a device which operating in cyclic process, maintains the temperature
of a hot body at a temperature higher than the temperature of surroundings
...

50
...


51
...

Heat extracted or rejected
COP = -------------------------------Work input
52
...
What is the relation between COPHP and COP ref?
Ans: COPHP = COPref +1
54
...

(ii) There are two processes to be carried out during compression and expansion
...
This speed variation during the same stroke of the piston is not
possible
...

55
...

Ans: (i) Efficiency can be increased as the higher temperature T2 increases
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56
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Therefore we can’t convert all the heat input into useful work
...
When will be the Carnot cycle efficiency is maximum?
Ans: Carnot cycle efficiency is maximum when the initial temperature is 0°K
...
What are the processes involved in Carnot cycle
...
Write the expression for efficiency of the carnot cycle
...
Define: Thermodynamic cycles
...

61
...

Ans: Compression ratio is the ratio between total cylinder volume to clearance volume
...
What is the range of compression ratio for SI and diesel engine?
Ans: For petrol of SI engine 6 to 8
For diesel engine 12 to 18
...
Which cycle is more efficient for the same compression ratio and heat input,
Otto cycle or Diesel cycle?
Ans: Otto cycle is more efficient than diesel cycle
64
...
The efficiency of the diesel cycle approaches the otto cycle efficiency when the
cut off ratio is ______
Ans: reduced
66
...
Which device is used to control the Air fuel ratio in the diesel engine?
Ans: Injection nozzle

68
...
C
...
What will be the speed of the
cam shaft?
Ans: 750 rpm
...
All the four operations in two stroke engine are performed in ________ number
of revolution of crank shaft
...
All the four operations in four stroke engine are performed in _______ number
of operations?
Ans: Two
71
...

Ans: Equal
72
...
What is meant by cutoff ratio?
Ans: Cutoff ratio is defined as the ratio of volume after the heat addition to before the
heat addition
...
What are the assumptions made for air standard cycle
...
Air is the working substance
...
Throughout the cycle, air behaves as a perfect gas and obeys all the gas laws
...
No chemical reaction takes place in the cylinder
4
...
The values of specific heats of the air remain constant throughout the cycle
...
What is the difference between otto and Diesel cycle
...
Otto cycle consist of two adiabatic and
two constant volume process
...
Compression ratio is equal to expansion
ratio
3
...

4
...
It is varies
from 6 to 8
...
It consists of two adiabatic, one constant
volume and one constant pressure
processes
...
Compression ratio is greater than
expansion ratio
...
Heat addition takes place at constant
pressure
4
...
It varies
from 12 to 18
...
What is the other name given to otto cycle?

Ans: Constant volume cycle
...
What is meant by air standard efficiency of the cycle?
Ans: It is defined as the ratio of work done by the cycle to the heat supplied to the cycle
...
Define: Mean effective pressure of an I
...
engine
...
It is also defined as the ratio of work done to the stroke
volume or piston displacement volume
...
What will be the effect of compression ratio on efficiency of the diesel cycle?
Ans: Efficiency increases with the increase in compression ratio and vice – versa
...
What will be the effect of cut off ratio on efficiency of the diesel cycle
...

81
...

Ans: Lesser
...
Define: Specific fuel consumption
...

83
...

Ans: Calorific value of a fuel is defined as the amount of heat liberated by the compete
combustion of unit quantity of a fuel
...
Give the expression for efficiency of the Dual cycle
...
The efficiency of the Dual cycle is _______ than the diesel cycle and ______ than
the otto cycle for the same compression ratio
...

86
...
Compression ratio 2
...
pressure ratio and 4
...

87
...

88
...

Ans:
1
Efficiency n = 1 - ---------- where Rp – pressure ratio
...
The two stroke cycle engine gives ______ the number of power strokes as
compared to the four stroke cycle engine, at the same engine speed
...

90
...
The diesel engine draws the mixture of diesel and air during suction stroke
(True / False)
Ans : False
...
What is the fuel injector?
Ans : Fuel injector is used in diesel engine to inject and atomize the diesel at the end of
the compression stroke
...
What is meant by SI engine ? Why it is called so ?
Ans : SI engine means spark ignition engine
...
It is also called as petrol engine
...
Give four major difference between two stroke and four stroke IC engine
...

2
For the same speed, twice the
number of power strokes are
produced than 4 stroke engine
...


Four Stroke cycle engine
One cycle is completed in four
stroke of the piston or two
revolution of the crank shaft
...

Turning moment is not uniform and
hence bigger flywheel is used
...


It contains valves which is operated
by valve mechanism
...
What is meant by CI Engine ? Why it is called so ?
Ans : CI engine means compression ignition engine
...
Hence it is called as compression ignition engine
...
What is a two stroke engine ?
Ans : A two stroke engine is an engine in which one cycle of operation is completed in
two stroke of the piston or one revolution of the crank shaft
...
What is a four stroke engine ?
Ans : A four stroke engine is an engine in which one cycle of operation is completed in
four stroke of the piston or two revolution of the crank shaft
...
Name the four strokes of an IC engine?
Ans : Suction, compression, power and exhaust stroke
...
Differentiate petrol and Diesel engines
...
Combustion of air fuel mixture takes
place by spark produced by sparkplug
...
Carburetor is used to mix the air fuel
mixture
...
Compression ratio varies from 6 to 8
...
It works on Otto cycle
...
Combustion takes place by high
compressed air
...
Fuel injector is used to inject the fuel in
atomized form
...
Compression ratio varies from 12 to 18
...
It works on Diesel or Dual cycle
...
What is a Gas turbine? How do you classify
...

Classification of gas turbine
...
According to the cycle of operation
a) open cycle b) closed cycle and c) semi – closed cycle
...
According to the process
a) constant volume and b) constant pressure process
...
What is meant by closed cycle gas turbine?
Ans: In closed cycle gas turbine, the same working fluid is recirculated again and again
...
What is meant by open cycle gas turbine?

Ans: In open cycle gas turbine, the exhaust gas form turbine is exhausted to the
atmosphere and fresh air is taken in compressor for every cycle
...
Gas turbine is working on ----cycle
Ans: Brayton or Jules cycle
...
How can we increase the efficiency of the gas turbine?
Ans: By providing inter cooler, re-heater along with heat exchanges
...
Differentiate open and closed cycle gas turbines
...
Working substance is exhausted to the
atmosphere after one cycle
...
Pre-cooler is not required
3
...
For the same power developed size and
weight of the plant is small

Closed cycle gas turbine
1
...

2
...

3
...
Size and weight are bigger
...
What is the function of intercooler in gas turbines? Where it is placed?
Ans: The intercooler is placed between L
...
and H
...
compressors
...
P
...

107
...
The
re-heater is placed between the H
...
and L
...
turbines to increase the enthalpy of the
exhaust gas coming from H
...
turbine
...
Turbine output is increased for the same compression ratio
2
...

108
...
It increases fuel economy
and increase thermal efficiency
...
What is meant by single acting compressor?
In single acting compressor, the suction, compression and delivery of air take place on
one side of the piston
...
What is meant by double acting compressor?
In double acting reciprocating compressor, the suction compressin and delivery of air
take place on both side of the piston
...
What is meant by single stage compressor?

In single stage compressor, the compression of air from the initial pressure to the final
pressure is carried out in one cylinder only
...
Define clearance ratio
Clearance ratio is defined as the ratio of clearance volume to swept volume (or) stroke
volume
...
What is compression ratio?
Compression ratio is defined as the ratio between total volume and clearance volume
...
What are the factors that effect the volumetric efficiency of a reciprocating
compressor?
1) Clearance volume 2) Compression ratio
...
Compressor Capacity is
a) Volume of air delivered
b) Volume of air sucked
c) Both a and b
d) Nine of the above
Ans: (a)
116
...
Compressor capacity is expressed in ___________
Ans: m3/min
118
...

119
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Ans: a)
120
...
In gas turbine, type of rotary compressor used is __________
Ans: Axial flow compressor
...
In Aeroplane, type of rotary compressor used is ___________
Ans: Axial flow compressor
...
What is the difference between complete (or) perfect inter cooling and
incomplelte (or) imperfect inter cooling
...

Imperfect Inter cooling
When the temperature of air leaving the inter cooler (T3) is more than original
atmospheric air temperature (T1), then the inter cooling is known as Imperfect inter
cooling
...
Power requirement of a refrigerator is _________
Ans: Inversely proportional to cop
125
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The capacity of a domestic refrigerator is in the range of __________
Ans: 0
...
3 tonnes
...
COP of a refrigerator working on a reversed carnot code is _________
Ans:
T2
----------T1 – T2
128
...
In vapour compression cycle the condition of refrigerant is dry saturated
vapour ________

Ans: Before entering the compressor
...
Give the 4 important parameters that are to be measured and controlled of an
air conditioning system
...
Temperature of air
2
...
Purity of air
4
...
Name the cycles on which an Air refrigeration system works
...
Reversed carnot cycle
2
...
Name four important properties of a good refrigerant
Ans: 1
...
High critical temperature & pressure
3
...
heat of liquid
4
...

133
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Filter
2
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Heating coil
4
...
Condeser
6
...
Name any four commonly used refrigerants
Ans; 1
...
Carbon di oxide (CO2)
3
...
Freon – 12
...
What are the factors to be considered in air conditioning a room?
Ans: 1
...
Humidity of air
3
...
Motion of air
...
The door of a running refrigerator inside a room was left open
...

137
...
A perfect black body is one which __________

Ans: Absorb heat radiation of all wave lengths falling on it
...
The valve of the wave length for maximum emissive power is given by ________
Ans: Wein’s Law
140
...
The unit for Stefan – Boltzman constant is ___________
Ans: Watt/m2/k4
142
...
The
heat transfer will take place mainly by _________
Ans: Radiation
...
Heat conducted through unit area and unit thick face per unit time when
temperature difference between opposite faces is unity is called _________
Ans: Thermal conductivity
144
...
What is meant by radiation shape factor?
The space factor is defined as the fraction of the radiative energy that is diffused from
one surface element and strikes the other surface directly with no intervening reflections
...
Other names for the radiation shape factor are view factor, angle
factor, and configuration factor
...
Give the 3 basic expressions governing the 3 modes of heat transfer
...
Newton’s Law of cooling
Q = hA(Ts - T∞)

Where
H – heat transfer co – eff in W/m2K
A – Surface Area in m2
Ts – Surface Temperature in K
T∞ - Fluid Temperature in K
3
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669 x 10-8 w/m2 k4
T – Temperature in K
147
...

1) A black body absorbs all incident radiation regardless of wave length and
direction
...

148
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1
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Nuclear Reaction
3
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149
...
Write down the Stefan Boltzman law with its Unit
The total energy emitted by a black body at a particular temperature is given by
Eb = σ T4
Where σ – Stefan Boltzman constant – 5

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