Chapter-1 of thermodynamics in engineering

Basic Concepts
Thermodynamics:
This subject is about conversion of Energy, and the laws governing it, In particular
conversion of heat into work and work into heat.
Work
Work
Work
Work Heat
Heat
Heat
Heat
.

Four laws that will be dealt in Thermodynamics are,
• Zero
Zeroth Law of Thermodynamics
th Law of Thermodynamics
• First
First Law of Thermodynamics
Law of Thermodynamics
• Second
Second Law of Thermodynamics
• Third
Third Law of Thermodynamics
The conversion of energy is governed by First and Second
Laws of Thermodynamics.

Classification of Thermodynamics
Thermodynamics
Classical Thermodynamics
Statistical Thermodynamics
In this, study is carried out on large
assemblage of atoms and it is also
termed as macroscopic approach
In this, study is carried out at the
molecular level and it is also termed
as microscopic approach

System, Surrounding and Boundary
System :
System :
• All engineering devices/Components are referred as Systems.
• A system is a finite quantity of matter or region upon which our
attention is focused.
Surrounding:
Surrounding:
• Things that are external to the system are referred as Surrounding.
Boundary:
Boundary:
• It is an interface between system and surrounding.
• System and surrounding interact through boundary.
• Boundary can be real (or) imaginary.
Boundary can be fixed (or) moving.

Based on the type of interaction, the systems are classified as
• CLOSED SYSTEM
• OPEN SYSTEM
• ISOLATED SYSTEM
Interaction
between
system and
surrounding
Mass Transfer
Energy Transfer
Heat
Work
Interaction Between System and Surrounding

Types of System
• CLOSED SYSTEM
CLOSED SYSTEM
No mass transfer occurs but only energy transfer occurs
Eg: A certain amount of gas enclosed in a cylinder piston arrangement.

Types of System
• OPEN SYSTEM
OPEN SYSTEM
Both mass transfer
mass transfer and energy transfer
energy transfer occurs.
eg: A certain amount of gas entering and leaving a
cylinder piston arrangement.

Types of System
• ISOLATED SYSTEM
ISOLATED SYSTEM
Neither mass transfer
mass transfer nor energy transfer
energy transfer occurs.
eg:If our entire universe is considered as a single system then it
is an isolated system.

Various Systems-Comparison
Note:
Note:
Mass Transfer Energy Transfer Type of System
No
No Yes
Yes Closed System
Closed System
Yes
Yes Yes
Yes Open System
Open System
No
No No
No Isolated System
Isolated System
Yes
Yes No
No Impossible
Impossible

Basic Concepts
Control Volume:
Control Volume:
If the volume of the system under study remains constant
then it is called CONTROL VOLUME.
Control Surface:
Control Surface:
The surface that bounds the control volume is called
CONTROL SURFACE.
Pure Substance:
Pure Substance:
A substance which has uniform chemical composition
throughout its mass.

Thermodynamic Equilibrium
A system is said to be in thermodynamic equilibrium if it is in
the following equilibriums
Thermal Equilibrium
Mechanical Equilibrium
Chemical Equilibrium

Thermal Equilibrium:
Thermal Equilibrium:
The temperature at all points of the system remains the
same and does not change with time.
Mechanical Equilibrium:
Mechanical Equilibrium:
No unbalanced forces acts within the system or between
system and surrounding.
Chemical Equilibrium:
Chemical Equilibrium:
No chemical reaction takes place within the system.

Basic Concepts
State:
State:
The condition or characteristics of a system is called State.
Property:
Property:
• The characteristics of a system is defined by property
• There are two different types of properties
• Intensive Properties
• Extensive Properties

Basic Concepts
Intensive Properties:
Intensive Properties:
These properties are independent of mass.
eg: Temperature, Pressure, Density etc.,
Extensive Properties:
Extensive Properties:
These properties are dependent of mass.
eg: Volume, Enthalpy, Entropy etc.,

Basic Concepts
PATH
PATH
• It is the succession of intermediate states
passed during a change of state.
(OR)
• It is the loci of intermediate states passed
during a change of state.

Basic Concepts
PROCESS
PROCESS
If the path followed by the system during change of
state is specified or defined completely, then it is
called a process.
eg: Constant pressure process
Constant temperature process
Constant volume process
Adiabatic process
Polytropic process

Basic Concepts
CYCLE
CYCLE
Series of processes executed by the system in such
a way that the initial and final states of the system
are same.

Quasi-Static Process
• This is a hypothetical (theoretical) process
• This is an Ideal Process
• A process is said to be quasi-static if the process
occurs at infinite slowness
occurs at infinite slowness
+
has infinite no. of intermediate equilibrium states
has infinite no. of intermediate equilibrium states
+
Reversible
Reversible

Point and Path Function
Differential Functions
Point Function
or
Exact Differential
Path Function
or
Inexact Differential

Point and Path Function
Point Function
Point Function
This depend on the end states only and does not depend
upon the path followed by the system
eg: All thermodynamic properties
thermodynamic properties are Point Function
Point Function
Path Function
Path Function
This depends on both the path followed by the system and
end states also.
eg: Heat and Work
Heat and Work are Path Functions.
Path Functions.

Heat & Work Transfer
Work Transfer
Work Transfer:
:
• Work transfer is energy in transit.
Work transfer is energy in transit.
• Work transfer is a form of energy transfer, which can be felt
Work transfer is a form of energy transfer, which can be felt
only in the boundary
only in the boundary.
.
Thermodynamic Work
Thermodynamic Work:
:
Work is said to be done if the net effect on the surrounding is
Work is said to be done if the net effect on the surrounding is
tantamount to the lifting of a weight through a certain height
tantamount to the lifting of a weight through a certain height
against the gravity.
against the gravity.

Expression for pdV Work
2
12
1
( *piston area* )
* *
=
W dW
p displacement
p A dL
pdV
W pdV










Work done during various Quasi-static Processes
The various quasi static processes are
• Constant Pressure Process (
Constant Pressure Process (Isobaric Process
Isobaric Process)
)
• Constant Volume Process (
Constant Volume Process ( Isochoric Process
Isochoric Process)
)
• Constant Temperature Process (
Constant Temperature Process ( Isothermal Process
Isothermal Process)
)
• Adiabatic Process (
Adiabatic Process (Isentropic Process
Isentropic Process)
)
• Polytropic Process
Polytropic Process

Constant Pressure Process
∫pdV
v1
v2
W12 = = p ( V2-V1)

Constant Volume Process
∫pdV
v1
v2
W12 = = 0

Constant Temperature Process
2
1
2
1
v2
v1
2
1
----------------(1)
but pV = C ; p =
sub in (1)
W = C
[ln ( V )]
V
ln
V
W pdV
C
V
dV
V
W pV
W PV


 
 
  
 
 
 
 



Polytropic Process
2
1
2
1
2
1
1
1 1
2 1
2 2 1 1
pV ; p = C V
W =
1
1
1
n n
n
V
n
V
n n
n
W pdV
but C
CV dV
V
W C
n
V V
W pV
n
p V pV
W
n


 
 


 
  
 
 
 

  

 






Flow Work
• Devices like pump, compressor, blower imparts
energy
energy to the fluid and drives the fluid across the
control volume. This energy (work) is called flow
work.
• Flow work = PV

Free Expansion Process
Expansion of gases in to a vacuum chamber does not
offer any resistance for expansion. Such expansion is
called unrestrained expansion or free expansion.
During this expansion Work transfer is zero
zero.
W
W12
12 = 0
= 0

Heat Transfer
• Energy transfer by virtue of temperature difference
is called Heat Transfer.
• Heat Transfer is also a boundary phenomenon.
• Difference in temperature is the CAUSE
CAUSE
Heat Transfer is the EFFECT.
EFFECT.
• Modes of Heat Transfer are Conduction, Convection
Conduction, Convection
and Radiation.
Radiation.

Specific Heat
• It is the amount of heat required to raise the
temperature of unit mass of a substance by unit
degree.
• For Solids and Liquids
cp = cv = c
• For Gases
cp – specific heat capacity at constant pressure
cv – specific heat capacity at constant volume
cp ≠ cv

Latent Heat
• It is the amount of heat transferred to cause a phase
change.
Latent Heat Latent Heat of Vaporization
Latent Heat of Fusion
Latent Heat of Sublimation

Latent Heat of Fusion
Solid
Solid Liquid
Liquid
Melting
Freezing
Liquid Vapour
Boiling
Condensation
Latent Heat of Vaporization
Latent Heat of Vaporization
Solid Vapour
Sublimation
Deposition

Sign Convention
• For Work Transfer,
For Work Transfer,
– Work done by the system is positive.
positive.
– Work done on the system is negative.
negative.
S
S
Y
Y
S
S
T
T
E
E
M
M
Win
Wout
-ve
+ve

Sign Convention
• For Heat Transfer
For Heat Transfer
– Heat supplied to the system is positive.
positive.
– Heat rejected by the system is negative.
negative.
S
Y
S
T
E
M
Qin
Qout
+ve
-ve

Chapter-1 of thermodynamics in engineering

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