ME33 ENGINEERING THERMODYNAMICS
1. What is meant by Thermodynamics?
Thermodynamics is the science of energy transfer and its effects
on physical properties
of substances.
2. Define the term thermal engineering.
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.
3. What is meant by Macroscopic approach in
thermodynamics?
Macroscopic thermodynamics deals with the effects of the
action of many molecules
concerned.
4. The two approaches by which the behaviour of matter can
be studied in thermodynamics are
................. and ........................
[Ans: Macroscopic, Microscopic]
5. What is Microscopic (or) Statistical thermodynamics?
Microscopic approach in thermodynamics deals with the study
of the behaviour of the
system by summing up the behaviour of each molecule
6. Give few applications of thermodynamic laws and
principles:
The laws and principles are applied in the steam and nuclear
power plants, IC engines,
Gas turbines, refrigeration etc.
7. What is thermodynamic medium?
A matter of growing material chosen for the conversion of one
form of energy into
another is called thermodynamic medium.
8. What is meant by thermodynamic system?
Thermodynamic system is defined as the any space or matter or
group of matter where
the energy transfer or energy conversions are studied.
9. Define thermodynamic system.
A thermodynamic system is defined as a quantity of matter or a
region in space, on
which the analysis of the problem is concentrated.
10. How do you classify thermodynamic system?
It may be classified into three types.
a. Closed system (only energy transfer and no mass transfer)
b. Open system (Both energy and mass transfer)
c. Isolated system (No mass and energy transfer)
11. What is meant by closed system? Give an example.
When a system has only heat and work transfer, but there is no
mass transfer, it is
called as closed system.
Example: Piston and cylinder arrangement.
Compression of a gas in a piston -. cylinder arrangement.
12. What is meant by open system? Give an example.
When a system has both mass and energy transfer it is called as
open system.
Example: Air Compressor.
13. Differentiate closed and open system.
Closed System Open System
1. There is no mass transfer. Only heat and
work will transfer.
1. Mass transfer will take place, in addition to
the heat and work transfer.
2. System boundary is fixed one 2. System boundary may or
may not change.
3. Example: Piston & cylinder arrangement,
Thermal power plant
3. Example: Air compressor, boiler
14. What is meant by isolated system? Give an example.
Isolated system is not affected by surroundings. There is no
heat; work and mass
transfer take place. In this system total energy remains constant.
Example: Entire Universe
15. Explain homogeneous and heterogeneous system.
The system consist of single phase is called homogeneous
system and the system consist of
more than one phase is called heterogeneous system.
16. What is boundary?
System and surroundings are separated by an imaginary line is
called boundary.
17. What is meant by surroundings?
Any other matter outside the system boundary is called as
surroundings.
18. What is universe ?
A system and· its surroundings together is called an universe.
19. What are the various types of open system?
The types of open system are:
a. Steady fiow system
b. Unsteady flow system.
20. In an isolated system, the total energy of the
system............................
Ans: remains constant.
21. What is meant by control volume?
Control volume is an imaginary region within which interactions
are studied.
22. What is known as control surface?
The boundary of the control volume is called as control surface.
23. Define change of state of a system
Any process in which one or more of the properties of the
system changes is
called change of state.
24. What is meant by thermodynamic property?
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.
25. How do you classify the property?
Thermodynamic property can be classified into two types.
a. Intensive or Intrinsic property
b. Extensive and Extrinsic property
26. What is meant by intensive or intrinsic property? Give
an example.
The properties which are independent on the mass of the system
is called intensive
properties.
Example: Pressure, Temperature, Specific Volume etc.
27. What is meant by extensive or extrinsic property? Give
an example.
The properties which are dependent on the mass of the system
are called extensive
properties.
Example: Total energy, Total volume, weight etc.
28. What do you understand by equilibrium of a system?
When a system remains in equilibrium state, it should not
undergo any charges to its
own accord.
29. Define thermodynamic equilibrium.
If a system is in Mechanical, Thermal and Chemical Equilibrium
then the system is in
thermodynamically equilibrium.
(Or)
If the system is isolated from its surrounding there will be no
change in the macroscopic
property, then the system is said to exist in a state of
thermodynamic equilibrium.
30. Differentiate Intensive and Extensive properties
Intensive Properties Extensive Properties
1. Independent on the mass of the system Dependent on the
mass of the system.
2. If we consider part of the system these
properties remain same.
Example: pressure, Temperature specific
volume etc.,
If we consider part of the system it will have a
lesser value.
Example: Total energy, Total volume, weight
etc.,
3. Extensive property/mass is known as intensive property
31. What are the conditions for thermodynamic
equilibrium?
The system in thermodynamic equilibrium must essentially be in
a. Mechanical Equilibrium
b. Thermal equilibrium
c. Chemical equilibrium
32. What is meant by thermodynamic equilibrium?
When a system is in thermodynamic equilibrium, it should
satisfy the following three
conditions.
a. Mechanical Equilibrium: - Pressure remains constant
b. Thermal equilibrium: - Temperature remains constant
c. Chemical equilibrium: There is no chemical reaction.
33. Explain Mechanical equilibrium.
If the forces are balanced between the system and surroundings
are called Mechanical
equilibrium
34. Explain Chemical equilibrium.
If there is no chemical reaction or transfer of matter form one
part of the system to
another is called Chemical equilibrium
35. Explain Thermal equilibrium.
If the temperature difference between the system and
surroundings is zero then it is in
Thermal equilibrium.
36. when there is uniform pressure at all points of the
system, then it is said to be in .........
Ans: Mechanical equilibrium
37. When a system wiII be in a state of thermodynamic
equilibrium?
A system is said to exist in a state of thermodynamic
equilibrium, when no change in any
microscopic property is registered, if the system is isolated from
the surroundings.
38. Define nuclear equilibrium
A system is said to be in nuclear equilibrium when nuclear
reactions such as fusion,
fission reaction does not cause any change.
39. Define magnetic equilibrium
A system is said to be in magnetic equilibrium when the
magnetisation and
demagnetisation effects do not change its properties
40. Define continuum
The Atomie structure of a substance is disregarded in classical
thermodynamics and the
substance is viewed to be a continuous, homogenous matter
without microscopic holes. This
concept is called as continuum.
41. Define the term process
It is defined as the change of state undergone by a gas due to
energy flow.
42. Define the term thermodynamic Cycle
When a system undergoes a series of processes and return to its
initial condition, it is
known as thermodynamic cycle.
43. What is meant by open cycle?
In an open cycle, the same working substance will be exhausted
to the surroundings
after expansion.
44. What is meant by closed cycle?
In a closed cycle, the same working substance will recalculates
again and again.
45. What is meant by reversible process?
A process is said to be reversible, it should trace the same path
in the reverse direction
when the process is reversed. It is possible only when the system
passes through a continuous
series of equilibrium state.
46. What is meant by irreversible process?
If a system does not pass through continuous equilibrium state,
then the process is said
to be irreversible.
47. What is meant by Point function?
The quantity which is independent on the process or path
followed by the system is
known as point functions.
Example: Pressure, volume, temperature, etc.,
48. What is meant by Path function?
The quantities which are dependent on the process or path
followed by the system is
known as path functions.
Example: Heat transfer, work transfer.
49. What is Quasi – Static process?
The process is said to be quasi – static, it should proceed
infinitesimally slow and follows
continuous series of equilibrium states. A quasi- static process is
that a succession of equilibrium
states. A quasi-static process is also called as reversible process.
50. State True or False:
Quasi static process is also called as Reversible process.
[Ans: True]
51. Define pure substance
A pure substanee is a homogenous and invariable chemical
composition through out
the mass.
52. Define absolute pressure
The total algebric sum of the atmospherie pressure and gauge
pressure is called
absolute pressure.
53. What is gauge pressure?
The pressure measured above the atmospherie pressure gauge
pressure.
54. Define atmospheric pressure
Pressure exerted by air on a column of 760 mm of mercury is
called atmospherie
pressure.
55. What is meant by state of a system?
State is an unique condition of the system and at equilibrium. It
can be identified by its
properties, such as pressure, volume.
56. Define path of change of state
The succession equilibrium states passed through, is called the
path of change of state.
57. Define energy
Energy of system is the ability or capacity to do work.
58. Define stored energy
Energy possessed by a system within its boundaries is called
stored energy.
Example: Potential energy.
59. Define power
The rate of energy transfer is called power.
60. Define transit energy
Energy possessed by a system which is capable of crossing its
boundaries is.caIled transit
energy.
Example: Heat energy, Electrical energy'.
61. Define internal energy
Energy possessed by a substance due to its molecular
arrangement and. motion of its
molecules is called internal energy.
62. What is meant by thermodynamic work?
A thermodynamic work is said to be do ne by a system if its sole
effect outside its
boundary is equivalent to raising a weight against the force of
gravity.
63. Work done by a system is.............
Ans: Positive.
64. Work done on a system is ...............
Ans: Negative
65. What is the work done in a closed system in terms
pressure and volume?
Workdone = Pdv.
66. Zeroth law is the basic of ................. measurement.
Ans: Temperature
67. Heat supplied to the system is......................
Ans: Positive.
68. Heat rejected by the system is....................
Ans: Negative
69. State True or False:
Heat and work are not properties of the system.
Ans: True
70. State True or False:
During all adiabatic process, the change in internal energy is
equal to work done.
Ans: True
71. State True or False:
During an isothermal process, the net heat interchange is el to
the work done by the
system.
Ans: True
72. Work done is a ------------------- function.
Ans: Path
73. Define mean effective pressure.
The mean effective pressure.of a cycle is defined as the average
pressure acting on the
piston which produces the same amount of work as that
produced by the actual varying
pressure during the cycle.
74. Define specific heat
The heat required by a'unit mass of a substanee to raise its tem .
perature by one
degree is called the specific heat of subs.tance
Unit: kJ I kg I K.
75. Define Latent heat
Latent heat is the amount of energy required to convert liquid
completely into
vapour per unit mass of a substance at a given pressure.
76. What is Triple point?
The point at which Solid, liquid and vapour phases are
equilibrium is called as triple point.
77. Explain Zeroth Law of thermodynamics?
Zeroth law of thermodynamics states that when two systems are
separately in thermal
equilibrium with a third system, then they themselves is in
thermal equilibrium with each other.
78. State the First law of thermodynamics
First law of thermodynamics states that when system undergoes
a cyclic process the net
heat transfer is equal to work transfer.
79. What are the limitations of first law of thermodynamics?
a. According to first law of thermodynamics heat and work are
mutually convertible during any
cycle of a closed system. But this law does not specify the
possible conditions under which
the heat is converted into work.
b. According to the first law of thermodynamics it is impossible
to transfer heat from lower
temperature to higher temperature.
c. It does not give any information regarding change of state or
whether the process is
possible or not.
d. The law does not specify the direction of heat and work.
80. Define the term enthalpy?
The Combination of internal energy and flow energy is known
as enthalpy of the system.
It may also be defined as the total heat of the substance.
Mathematically,
Enthalpy (H) = U + pv ……..KJ
Where, U – internal energy
p – Pressure
v – Volume
In terms of Cp & T → H = mCp (T2-T1) ……… KJ
81. Define the term internal energy
Internal energy of a gas is the energy stored in a gas due to its
molecular interactions. It
is also defined as the energy possessed by a gas at a given
temperature.
82. Define Heat.
Heat is the energy crossing the boundary due to the temperature
difference between
the system and surroundings.
83. What is meant by thermodynamic work?
It is the work done by the system when the energy transferred
across the boundary of
the system. It is mainly due to intensive property difference
between the system and
surroundings.
84. Define Specific heat capacity at constant pressure.
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 the pressure
kept constant. It is denoted
by Cp.
85. Define Specific heat capacity at constant volume.
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.
86. What do you understand by pure substance?
A pure substance is defined as one that is homogeneous and
invariable in chemical
composition throughout its mass.
87. Define entropy of a pure substance.
Entropy is an important thermodynamic property, which
increases with addition of heat
and decreases with its removal. Entropy is a function of
temperature only. It is an unavailability
of energy during energy transfer.
88. Define PMM of first kind
PMM of first kind delivers work continuously without any input.
It violates first law of
thermodynamics, it is impossible to construct an engine working
with this principle.
89. What is perpetual motion machine of first kind?
It is defined as a machine, which produces work energy without
consuming an
equivalent of energy from other source. It is impossible to obtain
in actual practice, because no
machine can produce energy of its own without consuming any
other form of energy.
90. What is Perpetual motion machine of the second kind?
A heat engine, which converts whole of the heat energy into
mechanical work, is known
as Perpetual motion machine of the second kind.
91. Give the general gas energy equations.
dH = dE + dW.
92. State the law of conservation of energy
Energy can neither be created nor destroyed, but it can be
transferred from one form to
another.
93. Define an isentropic process.
Isentropic process is also called as reversible adiabatic process.
It is a process which
follows the law of pVy = C is known as isentropic process.
During this process entropy remains
constant and no heat enters or leaves the gas.
94. Explain the throttling process.
When a gas or vapour expands and flows through an aperture of
small size, the process
is called as throttling process.
95. Work done in a free expansion process is _________
Ans: Zero
96. Define free expansion process.
When a gas expands suddenly into a vacuum through a large
orifice is known as free
expansion process.
97. Which property is constant during throttling?
Enthalpy
98. If in the equation PVn = C, the value of n = then the
process is called _______
Constant Volume process
99. The polytropic index (n) is given by ________
n = log (P2/P1)/ log (V1/V2)
100. Work transfer is equal to heat transfer in case of
________ process.
Isothermal process
101. Write down the characteristic gas equation.
Characteristic gas equation is pV = mRT
Where,
p = pressure
V = Volume
R = Characteristic gas constant
T = Temperature.
102. What is a steady flow process?
Steady flow means that the rates of flow of mass and energy
across the control surface
are constant.
103. What is meant by steady flow process?
During the process the rate of flow of mass and energy across
the boundary remains
constant, is known as steady flow process.
104. Prove that for an isolated system, there is no change in
internal energy.
In isolated system there is no interaction between the system and
the surroundings.
There is no mass transfer and energy transfer.
According to first law of thermodynamics as
dQ = dU + dW; dU = dQ - dW; dQ = 0, dW = 0,
Therefore dU = 0 by integrating the above equation U =
constant, therefore the internal
energy is constant for isolated system.
105. Indicate the practical application of steady flow energy
equation.
a. Turbine
b. Nozzle
c. Condenser
d. Compressor
106. What is the difference between steady flow and non –
flow process?
During the steady flow process the rate of flow of mass and
energy across the boundary
remains constant.
In case of non – flow across the system and boundary.
UNIT II
1. State the Kelvin – Plank statement of second law of
thermodynamics
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.
2. Define Kelvin Planck Statement.
It is impossible to construct a heat engine to produce network in
a complete cycle if it
exchanges heat from a single reservoir at single fixed
temperature.
3. State Clausius statement of second law of
thermodynamics.
It states that heat can flow from hot body to cold without any
external aid but heat
cannot flow from cold body to hot body without any external
aid.
4. Define Claussius statement.
It is impossible for a self-acting machine working in a cyclic
process, to transfer heat
from a body at lower temperature to a body at a higher
temperature without the aid of an
external agency.
5. State Carnot theorem.
It states that no heat engine operating in a cycle between two
constant temperature
heat reservoirs can be more efficient than a reversible engine
operating between the same
reservoirs.
6. State Carnot’s theorem.
No heat engine operating in a cyclic process between two fixed
temperatures can be
more efficient than a reversible engine operating between the
same temperature limits.
7. What are the Corollaries of Carnot theorem?
a. In all reversible engine operating between the two given
thermal reservoirs with fixed
temperature, have the same efficiency.
b. 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.
8. Define – PMM of second kind.
Perpetual motion machine of second kind draws heat
continuously from single reservoir
and converts it into equivalent amount of work. Thus it gives
100% efficiency.
9. What is the difference between a heat pump and a
refrigerator?
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.
A refrigerator is a device which operating in a cyclic process,
maintains the temperature
of a cold body at a temperature lower than the temperature of the
surroundings.
10. Define Heat pump.
A heat pump is a device, which is working in a cycle and
transfers heat from lower
temperature to higher temperature.
11. Define Heat engine.
Heat engine is a machine, which is used to convert the heat
energy into mechanical
work in a cyclic process.
12. What is meant by heat engine?
A heat engine is a device which is used to convert the thermal
energy into mechanical
energy.
13. What are the assumptions made on heat engine?
a. The source and sink are maintained at constant temperature.
b. The source and sink has infinite heat capacity.
14. Define the term COP?
Co-efficient of performance is defined as the ratio of heat
extracted or rejected to work
input.
Heat extracted or rejected
COP = -------------------------------Work input
15. Write the expression for COP of a heat pump and a
refrigerator?
COP of heat pump
Heat Supplied T2
COP HP = ------------------- = -------Work input T2-T1
COP of Refrigerator
Heat extracted T1
COP HP = --------------- = -------Work input T2-T1
16. What is the relation between COPHP and COP ref?
COPHP = COPref +1
17. Why Carnot cycle cannot be realized in practical?
a. In a Carnot cycle all the four processes are reversible but in
actual practice there is no
process is reversible.
b. There are two processes to be carried out during compression
and expansion. For
isothermal process the piston moves very slowly and for
adiabatic process the piston moves
as fast as possible. This speed variation during the same stroke
of the piston is not possible.
c. It is not possible to avoid friction moving parts completely.
18. Name two alternative methods by which the efficiency of
a Carnot cycle can be increased.
a. Efficiency can be increased as the higher temperature T2
increases.
b. Efficiency can be increased as the lower temperature T1
decreases.
19. Why a heat engine cannot have 100% efficiency?
For all the heat engines there will be a heat loss between system
and surroundings.
Therefore we can’t convert all the heat input into useful work.
20. When will be the Carnot cycle efficiency is maximum?
Carnot cycle efficiency is maximum when the initial
temperature is 0°K.
21. What are the processes involved in Carnot cycle.
Carnot cycle consist of
a. Reversible isothermal compression
b. Isentropic compression
c. Reversible isothermal expansion
d. Isentropic expansion
22. Write the expression for efficiency of the carnot cycle.
T2 – T1
n = --------T2
23. What are the limitations of Carnot cycle?
a. No friction is considered for moving parts of the engine.
b. There should not be any heat loss.
24. What is meant by reversible process?
A reversible process is one, which is performed in such a way
that at the conclusion of
process, both system and surroundings may be restored to their
initial state, without producing
any changes in rest of the universe.
25. What is meant by irreversible process?
The mixing of two substances and combustion also leads to
irreversibility. All
spontaneous process is irreversible.
26. What is absolute entropy?
The entropy measured for all perfect crystalline solids at
absolute zero temperature is
known as absolute entropy.
27. Explain entropy?
It is an important thermodynamic property of the substance. It is
the measure of
molecular disorder. It is denoted by S. The measurement of
change in entropy for reversible
process is obtained by the quantity of heat received or rejected
to absolute temperature.
28. Define availability.
The maximum useful work obtained during a process in which
the final condition of the
system is the same as that of the surrounding is called
availability of the system.
29. Define available energy and unavailable energy.
Available energy is the maximum thermal useful work under
ideal condition. The
remaining part, which cannot be converted into work, is known
as unavailable energy.
30. Explain the term source and sink.
Source is a thermal reservoir, which supplies heat to the system
and sink is a thermal
reservoir, which takes the heat from the system.
31. What do you understand by the entropy principle?
The entropy of an isolated system can never decrease. It always
increases and remains
constant only when the process is reversible. This is known as
principle of increase in entropy or
entropy principle.
32. What are the important characteristics of entropy?
a. If the heat is supplied to the system then the entropy will
increase.
b. If the heat is rejected to the system then the entropy will
decrease.
c. The entropy is constant for all adiabatic frictionless process.
d. The entropy increases if temperature of heat is lowered
without work being done as in
throttling process.
e. If the entropy is maximum, then there is a minimum
availability for conversion in to
work.
f. If the entropy is minimum then there is a maximum
availability for conversion into work.