Title: 06ME 33: Basic Thermodynamics
106ME 33 Basic Thermodynamics
VIJAYAVITHAL BONGALE
Assistant Professor Department of
Mechanical Engineering Malnad College of
Engineering Hassan 573201 Email
vvb_at_mcehassan.ac.in Fax 08172 -245683 Phone (O)
08172-245319 Mobile 9448821954
206ME 33 Basic Thermodynamics
Second law of thermodynamics
SESSION III
After this session one will be able to know the
- Irreversible process, its representation and cite
examples
- The Carnot Cycle and Efficiency
- Reversed Carnot Engine and COP
- Internal and External irreversibility
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
306ME 33 Basic Thermodynamics
IRREVERSIBLE PROCESS
Any process which is not reversible is an
irreversible process
The irreversibility of a process may be due to,
1. Lack of equilibrium during the process
2. Involvement of dissipative effects
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
406ME 33 Basic Thermodynamics
Examples are,
1. Movement of solids with friction
2. Flow of viscous fluids in pipes and passages
3. Mixing of two different substances
4. Heat transfer through a finite temperature
difference
5. Combustion process
6. Free expansion etc.
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
506ME 33 Basic Thermodynamics
IRREVERSIBLE PROCESSES
Irreversibility due to dissipative effects like
friction
Free expansion
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
6ME 33 Basic Thermodynamics
Irreversibility due to dissipation of electrical
work into internal energy
Irreversibility due to dissipation of stirring
work into internal energy
Vijayavithal Bongale, Asst. Professor
(Mechanical) MCE, Hassan
706ME 33 Basic Thermodynamics
Representation of an irreversible process
A
Y
B
X
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
806ME 33 Basic Thermodynamics
Proof that heat transfer through a finite
temperature difference is irreversible
Heat transfer through a finite temperature
difference
Heat transfer through a finite temperature
difference is irreversible
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
906ME 33 Basic Thermodynamics
Proof that Unrestrained expansion makes process
irreversible
Initial state
Reversed process
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1006ME 33 Basic Thermodynamics
Definitions
- Reversible Cycle
- One in which all the processes are reversible
- Irreversible Cycle
- One which contains at least one irreversible
process
- Reversible Engine
- An engine which works in a reversible cycle
- Irreversible Engine
- An engine which works in an irreversible cycle
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1106ME 33 Basic Thermodynamics
The Carnot Cycle and Efficiency
Processes 1. A reversible Isothermal process
(heat addition) 2. A reversible adiabatic
process (Expansion) 3. A reversible Isothermal
process (heat rejection) 4. A reversible
adiabatic process (Compression)
Carnot Engine-Stationery System
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1206ME 33 Basic Thermodynamics
Carnot engine Steady Flow System
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1306ME 33 Basic Thermodynamics
Carnot cycle on a property diagram
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1406ME 33 Basic Thermodynamics
Efficiency
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1506ME 33 Basic Thermodynamics
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1606ME 33 Basic Thermodynamics
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1706ME 33 Basic Thermodynamics
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1806ME 33 Basic Thermodynamics
Reversed Carnot engineSteady Flow process
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
1906ME 33 Basic Thermodynamics
Coefficient of Performance
Reversible Heat Engine
A Heat Engine which engages in heat transfer with
two systems of fixed, but different temperature,
is reversible if its efficiency when operating
directly equal to the reciprocal of its
COEFFICIENT OF PERFORMANCE when operating as a
heat pump.
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2006ME 33 Basic Thermodynamics
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2106ME 33 Basic Thermodynamics
FIRST LAW SECOND LAW EFFICIENCY
FIRST LAW EFFICIENCY or CONVERSION EFFICIENCY
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2206ME 33 Basic Thermodynamics
Why SECOND LAW EFFICIENCY?
Consider two engines, Engine A and Engine B
working with two thermal reservoirs as shown
Let the two engines have the same thermal
efficiency and is equal and 30
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2306ME 33 Basic Thermodynamics
The first law efficiency of 30 simply means that
both engines are performing equally well.
The best possible Efficiency is achieved when
engines perform as reversible (CARNOT) engines.
It is seen that Engine B has greater work
potential in it than Engine A, Engine B is
performing poorly compared to A even though both
have the same thermal efficiency.
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2406ME 33 Basic Thermodynamics
Thus, the first law is not a realistic measure of
the performance of engineering devices. To
overcome this deficiency the second law
efficiency is defined.
That is, Engine A converts 60 percent of the
available work potential into useful work,
whereas Engine B converts only 43 percent of the
available work potential into useful work
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2506ME 33 Basic Thermodynamics
The second law efficiency can also be expressed
as
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2606ME 33 Basic Thermodynamics
Internal and External reversibility
Internally Reversible Process No
irreversibility occurs within the boundaries of
the system during the process
Externally Reversible Process No
irreversibility occurs outside the boundaries of
the system during the process
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2706ME 33 Basic Thermodynamics
HEAT TRANSFER PROCESSES
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2806ME 33 Basic Thermodynamics
SUMMARY
- Any process which is not reversible is an
irreversible process
- Lack of equilibrium such as heat transfer through
a finite temperature difference, lack of pressure
equilibrium with in a system or between the
system surroundings, free expansion make a
process irreversible
- Involvement of dissipative effects such as
friction, stirring work and electrical work into
internal energy make a process irreversible
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
2906ME 33 Basic Thermodynamics
- Carnot cycle is a reversible cycle and Carnot
engine efficiency is the maximum but less than
100
- For a reversible heat engine,
- Understood First law and Second law efficiency
- Understood totally reversible and internally
reversible processes
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan
3006ME 33 Basic Thermodynamics
Email vvb_at_mcehassan.ac.in
vv_bongale2002_at_yahoo.co.in Fax 08172
-245683 Phone (o) 08172-245319 Mobile
9448821954
Vijayavithal Bongale, Asst. Professor in
Mechanical Engg, MCE, Hassan