Short Notes: Basic Concepts of Thermodynamics | Short Notes for Mechanical Engineering PDF Download

 Page 1


Basic Concepts of Thermodynamics 
Thermodynamics is a science dealing with Energy and its transformation and its 
effect on the physical properties of substances.
• It deals with equilibrium and feasibility of a process.
• Deals with the relationship between heat and work and the properties of 
systems in equilibrium.
Thermodynamics System
• It is defined as the quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called surrounding.
• Real or imaginary surface (mathematically thickness zero) that separates the 
system from the surrounding is called the boundary.
Closed System (Control Mass):
Page 2


Basic Concepts of Thermodynamics 
Thermodynamics is a science dealing with Energy and its transformation and its 
effect on the physical properties of substances.
• It deals with equilibrium and feasibility of a process.
• Deals with the relationship between heat and work and the properties of 
systems in equilibrium.
Thermodynamics System
• It is defined as the quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called surrounding.
• Real or imaginary surface (mathematically thickness zero) that separates the 
system from the surrounding is called the boundary.
Closed System (Control Mass):
• It consists of a fixed amount of mass and no mass can cross its boundary or 
leave or enter a closed system.
• Energy in the form of heat or work can cross the boundary and the volume of 
closed system does not have to be fixed
• Example: piston cylinder device.
Fixed
boundary
Open System (Control Volume):
• It is a properly selected region in the space and both mass and energy region 
can cross the boundary.
• The boundary of a control volume is called a control surface and they can be 
real or imaginary.
• Example: Compressor, turbine, nozzle.
A control volume can be fixed, in size and shape as in case of nozzle or it may 
involve moving boundaries as shown in Fig. (b).
Most control volume, however have fixed boundaries and thus do not involve any 
moving boundaries.
Imaginary
boundary Fixe'ired
(a) No £le
n
| \ i
;Moving boundary:
— ; Fixed boundary !
1
! / j
(b) Pistion
Properties of a System: Any characteristic of a system is called a property. It can 
be independent or dependent. •
• Intensive properties: Which are independent of the size of system such as 
temperature, pressure and density.
• Extensive properties: Whose values depend on the size or extent of the 
system such as mass m, volume V and total energy E.
Page 3


Basic Concepts of Thermodynamics 
Thermodynamics is a science dealing with Energy and its transformation and its 
effect on the physical properties of substances.
• It deals with equilibrium and feasibility of a process.
• Deals with the relationship between heat and work and the properties of 
systems in equilibrium.
Thermodynamics System
• It is defined as the quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called surrounding.
• Real or imaginary surface (mathematically thickness zero) that separates the 
system from the surrounding is called the boundary.
Closed System (Control Mass):
• It consists of a fixed amount of mass and no mass can cross its boundary or 
leave or enter a closed system.
• Energy in the form of heat or work can cross the boundary and the volume of 
closed system does not have to be fixed
• Example: piston cylinder device.
Fixed
boundary
Open System (Control Volume):
• It is a properly selected region in the space and both mass and energy region 
can cross the boundary.
• The boundary of a control volume is called a control surface and they can be 
real or imaginary.
• Example: Compressor, turbine, nozzle.
A control volume can be fixed, in size and shape as in case of nozzle or it may 
involve moving boundaries as shown in Fig. (b).
Most control volume, however have fixed boundaries and thus do not involve any 
moving boundaries.
Imaginary
boundary Fixe'ired
(a) No £le
n
| \ i
;Moving boundary:
— ; Fixed boundary !
1
! / j
(b) Pistion
Properties of a System: Any characteristic of a system is called a property. It can 
be independent or dependent. •
• Intensive properties: Which are independent of the size of system such as 
temperature, pressure and density.
• Extensive properties: Whose values depend on the size or extent of the 
system such as mass m, volume V and total energy E.
Divide the system into two equal parts with a partition to determine whether the 
property is intensive or extensive.
Extensive
properties
Intensive
properties
Distribution of extensive and intensive properties
Generally, upper case letters are used to denote extensive properties (exception m) 
and lower case letters are used for intensive properties (exception P, 7).
Extensive Property Intensive Property
Extensive properties are dependent on the mass of 
a system
Intensive properties are indep 
mass of a system
Extensive properties are additive Intensive properties are not at
Its value for an overall system is the sum of its 
values for the parts into which the system is 
divided
Its value remains the same wf 
considers the whole system o 
it.
Example:mass(m),volume(V),Energy(E),Enthalpy(H)
etc
Example:Pressure(P),Tempera 
etc
Uppercase letters are used for extensive properties 
except mass
Lowercase letters are used foi 
properties except pressure(P)
4 r_ ?
Specific Properties of a System: Extensive properties per unit mass are called 
specific properties.
• Specific volume:
m
• Specific energy:
E
—
m
• Specific gravity (or relative density): It is used to define the density of a 
substance with respect to density of some standard substance at a specified 
temperature. (Usually, water at 4°C,
Ph- _ o
= 1000 kg/m3 )
Continuum:
• Continuum is defined as a continuous, homogeneous matter with no holes.
• The continuum idealization allows us to treat properties as point function.
Page 4


Basic Concepts of Thermodynamics 
Thermodynamics is a science dealing with Energy and its transformation and its 
effect on the physical properties of substances.
• It deals with equilibrium and feasibility of a process.
• Deals with the relationship between heat and work and the properties of 
systems in equilibrium.
Thermodynamics System
• It is defined as the quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called surrounding.
• Real or imaginary surface (mathematically thickness zero) that separates the 
system from the surrounding is called the boundary.
Closed System (Control Mass):
• It consists of a fixed amount of mass and no mass can cross its boundary or 
leave or enter a closed system.
• Energy in the form of heat or work can cross the boundary and the volume of 
closed system does not have to be fixed
• Example: piston cylinder device.
Fixed
boundary
Open System (Control Volume):
• It is a properly selected region in the space and both mass and energy region 
can cross the boundary.
• The boundary of a control volume is called a control surface and they can be 
real or imaginary.
• Example: Compressor, turbine, nozzle.
A control volume can be fixed, in size and shape as in case of nozzle or it may 
involve moving boundaries as shown in Fig. (b).
Most control volume, however have fixed boundaries and thus do not involve any 
moving boundaries.
Imaginary
boundary Fixe'ired
(a) No £le
n
| \ i
;Moving boundary:
— ; Fixed boundary !
1
! / j
(b) Pistion
Properties of a System: Any characteristic of a system is called a property. It can 
be independent or dependent. •
• Intensive properties: Which are independent of the size of system such as 
temperature, pressure and density.
• Extensive properties: Whose values depend on the size or extent of the 
system such as mass m, volume V and total energy E.
Divide the system into two equal parts with a partition to determine whether the 
property is intensive or extensive.
Extensive
properties
Intensive
properties
Distribution of extensive and intensive properties
Generally, upper case letters are used to denote extensive properties (exception m) 
and lower case letters are used for intensive properties (exception P, 7).
Extensive Property Intensive Property
Extensive properties are dependent on the mass of 
a system
Intensive properties are indep 
mass of a system
Extensive properties are additive Intensive properties are not at
Its value for an overall system is the sum of its 
values for the parts into which the system is 
divided
Its value remains the same wf 
considers the whole system o 
it.
Example:mass(m),volume(V),Energy(E),Enthalpy(H)
etc
Example:Pressure(P),Tempera 
etc
Uppercase letters are used for extensive properties 
except mass
Lowercase letters are used foi 
properties except pressure(P)
4 r_ ?
Specific Properties of a System: Extensive properties per unit mass are called 
specific properties.
• Specific volume:
m
• Specific energy:
E
—
m
• Specific gravity (or relative density): It is used to define the density of a 
substance with respect to density of some standard substance at a specified 
temperature. (Usually, water at 4°C,
Ph- _ o
= 1000 kg/m3 )
Continuum:
• Continuum is defined as a continuous, homogeneous matter with no holes.
• The continuum idealization allows us to treat properties as point function.
• To assume properties to vary continually in space with no jump 
discontinuities.
State:
• State of system is described by its properties.
• At a given state, all the properties of a system have fixed values.
• However, there is no need to specify all the properties in order to fix a state.
• The number of properties required to fix the state of a system is given by the 
state postulates.
• It property varies, other should be held constant.
• In other words, the condition of a system at any instant of time is called its 
state.
Equilibrium:
• The word equilibrium implies a state of balance.
• In an equilibrium state, there are no unbalanced potentials (or driving forces) 
within the system.
• A system in equilibrium experience has no changes when it is isolated from 
its surrounding.
• Thermodynamics deals with equilibrium states.
• A system is in thermal equilibrium if the temperature is same throughout the 
entire system.
• In mechanical equilibrium, there is no change in pressure at any point of the 
system with time.
• In chemical equilibrium, no chemical reactions occur.
Processes: Any change that a system goes from one equilibrium state to another 
equilibrium state is called a process and series of states through which a system 
passes during a process is called the path of the process.
Quasi-Equilibrium Process: When a process proceeds in such a manner that the 
system remains infinitesimally close to an equilibrium state at all times, it is called 
a quasi-static or quasi equilibrium process.
^ i pi-*-
Slow compression 
(quasi equilibrium)
Very fast compression
(Non-quasi equilibrium)
Quasi equilibrium is an idealized process and is not a true representation of 
an actual process.
Quasi equilibrium processes are easy to analyze.
Page 5


Basic Concepts of Thermodynamics 
Thermodynamics is a science dealing with Energy and its transformation and its 
effect on the physical properties of substances.
• It deals with equilibrium and feasibility of a process.
• Deals with the relationship between heat and work and the properties of 
systems in equilibrium.
Thermodynamics System
• It is defined as the quantity of matter or a region in space chosen for study.
• The mass and region outside the system is called surrounding.
• Real or imaginary surface (mathematically thickness zero) that separates the 
system from the surrounding is called the boundary.
Closed System (Control Mass):
• It consists of a fixed amount of mass and no mass can cross its boundary or 
leave or enter a closed system.
• Energy in the form of heat or work can cross the boundary and the volume of 
closed system does not have to be fixed
• Example: piston cylinder device.
Fixed
boundary
Open System (Control Volume):
• It is a properly selected region in the space and both mass and energy region 
can cross the boundary.
• The boundary of a control volume is called a control surface and they can be 
real or imaginary.
• Example: Compressor, turbine, nozzle.
A control volume can be fixed, in size and shape as in case of nozzle or it may 
involve moving boundaries as shown in Fig. (b).
Most control volume, however have fixed boundaries and thus do not involve any 
moving boundaries.
Imaginary
boundary Fixe'ired
(a) No £le
n
| \ i
;Moving boundary:
— ; Fixed boundary !
1
! / j
(b) Pistion
Properties of a System: Any characteristic of a system is called a property. It can 
be independent or dependent. •
• Intensive properties: Which are independent of the size of system such as 
temperature, pressure and density.
• Extensive properties: Whose values depend on the size or extent of the 
system such as mass m, volume V and total energy E.
Divide the system into two equal parts with a partition to determine whether the 
property is intensive or extensive.
Extensive
properties
Intensive
properties
Distribution of extensive and intensive properties
Generally, upper case letters are used to denote extensive properties (exception m) 
and lower case letters are used for intensive properties (exception P, 7).
Extensive Property Intensive Property
Extensive properties are dependent on the mass of 
a system
Intensive properties are indep 
mass of a system
Extensive properties are additive Intensive properties are not at
Its value for an overall system is the sum of its 
values for the parts into which the system is 
divided
Its value remains the same wf 
considers the whole system o 
it.
Example:mass(m),volume(V),Energy(E),Enthalpy(H)
etc
Example:Pressure(P),Tempera 
etc
Uppercase letters are used for extensive properties 
except mass
Lowercase letters are used foi 
properties except pressure(P)
4 r_ ?
Specific Properties of a System: Extensive properties per unit mass are called 
specific properties.
• Specific volume:
m
• Specific energy:
E
—
m
• Specific gravity (or relative density): It is used to define the density of a 
substance with respect to density of some standard substance at a specified 
temperature. (Usually, water at 4°C,
Ph- _ o
= 1000 kg/m3 )
Continuum:
• Continuum is defined as a continuous, homogeneous matter with no holes.
• The continuum idealization allows us to treat properties as point function.
• To assume properties to vary continually in space with no jump 
discontinuities.
State:
• State of system is described by its properties.
• At a given state, all the properties of a system have fixed values.
• However, there is no need to specify all the properties in order to fix a state.
• The number of properties required to fix the state of a system is given by the 
state postulates.
• It property varies, other should be held constant.
• In other words, the condition of a system at any instant of time is called its 
state.
Equilibrium:
• The word equilibrium implies a state of balance.
• In an equilibrium state, there are no unbalanced potentials (or driving forces) 
within the system.
• A system in equilibrium experience has no changes when it is isolated from 
its surrounding.
• Thermodynamics deals with equilibrium states.
• A system is in thermal equilibrium if the temperature is same throughout the 
entire system.
• In mechanical equilibrium, there is no change in pressure at any point of the 
system with time.
• In chemical equilibrium, no chemical reactions occur.
Processes: Any change that a system goes from one equilibrium state to another 
equilibrium state is called a process and series of states through which a system 
passes during a process is called the path of the process.
Quasi-Equilibrium Process: When a process proceeds in such a manner that the 
system remains infinitesimally close to an equilibrium state at all times, it is called 
a quasi-static or quasi equilibrium process.
^ i pi-*-
Slow compression 
(quasi equilibrium)
Very fast compression
(Non-quasi equilibrium)
Quasi equilibrium is an idealized process and is not a true representation of 
an actual process.
Quasi equilibrium processes are easy to analyze.
• Quasi equilibrium processes are work producing devices deliver the maximum 
work when they operate on quasi equilibrium processes.
• Quasi equilibrium processes as standards to which actual processes can be 
compared.
Difference between Point Function Vs Path Function
E
V, V ------- Vl
Point Function Path Function
Any quantity whose change is 
independent of the path is known as 
point function
Any quantity, the value of which 
depends on the path followed during a 
change of state is known as path 
function
The magnitude of such quantity in a 
process depends on the state.
The magnitude of such quantity in a 
process is equal to the area under the 
curve on a property diagram
These are exact differential
These are inexact differential. Inexact 
differential is denoted by 5
Properties are the examples of point 
function like pressure(P), volume(V), 
Temp.(T),Energy etc.
Ex: Heat and work
Cycle: A system is said to have undergone a cycle if it returns to its initial state at 
the end of process i.e., for a cycle the initial and final states are identical.
Steady Flow Process: Steady flow process is defined as a process during which a 
fluid flows through a control volume steadily.
Temperature: The temperature is a measure (degree) of hotness or coldness, 
(freezing cold, warm hot)
Temperature Scales:
• They are related to absolute temperature scales.
• The temperature scales used in the SI and English system are the Celsius 
scale and the Fahrenheit scale, respectively.
• A scale of temperature independent of the thermometric substance is called a 
thermodynamic temperature scale.
• Kelvin scale is related to Celsius scale by
T(K) = T(C) + 273.16