1. The document discusses thermodynamics concepts including throttling process, heat engines, refrigerators, heat pumps, and the first and second laws of thermodynamics. 2. It defines key terms like throttling process, free expansion, heat source, heat sink, heat reservoir, thermal efficiency, and coefficient of performance. 3. Several statements of the second law are provided including Clausius statement and Kelvin-Planck statement.

1. Unit No:01
Thermodynamics
Prof. Yash B. Parikh
M.Tech (Computer Integrated Manufacturing)
B.E.(Mechanical Engineering)
Assistant Professor
Department of Mechanical Engineering

2. Throttling Process
2
 Whenever a substance expands from a region of
relatively high pressure across a restriction or small
opening under a steady flow without heat transfer.
e.g. the puncture of a tyre is a throttling process.
 The pressure drop takes place so rapidly that there is
neither sufficient time nor surface area for heat
transfer to take place.
 Throttling process is a.k.a. isenthalpic process.
 Expansion of a gas through a large opening is called
a free expansion.
e.g. bursting of tyre is the case of free expansion
process.

3. Throttling Process
3
 Only difference between the two is in free expansion
gas leaves with larger velocity whereas in throttling
change in velocity is negligible.

4. Limitations of First Law of Thermodynamics
4
 Heat is transferred from hot body to cooler
surroundings. However reverse of this is not possible.
 In Joules experiment, reverse process is not possible.
i.e. raising the weight by transferring heat from fluid
to the paddle wheel is not possible.
1. The processes can proceed in a particular direction
only.
2. All processes involving conversion of heat into work
& vice-versa are not equivalent.

5. Second Law of Thermodynamics
5
 According to First law of thermodynamics heat and
work are mutually interchangeable.
 This law does not mention about the direction flow of
heat.
 Second law of thermodynamics gives the direction of
flow of heat energy.
 It is important to understand how heat energy is
converted into mechanical work.

6. Heat Engine
6
 Heat engine is a device used for converting heat
energy constantly into mechanical work.
 Three essential parts of a heat engine are :
Source (Hot Body) , Sink (Cold Body) & Working
Substance.

7. Heat Engine
7
 Heat Source : A heat reservoir which supplies heat to
a system.
 Heat Sink: A heat reservoir which absorbs heat from
a system.
 Heat Reservoir : The source of infinite heat energy.
Finite amount of heat absorbed or rejected will not
affect its temperature
e.g. Ocean, Lakes, Atmosphere.

8. Thermal Efficiency of a Heat Engine
8
 Heat energy is never converted completely into
mechanical energy.
i.e. efficiency of heat engine is never equals to 100%.
It’s given by,
Efficiency = External W.D. / Heat absorbed from Source

9. Statements of Second Law
9
1. Clausius Statement :
It is impossible to construct a device operating on a
cycle whose sole effect is the transfer of heat from a
low temperature heat reservoir to a higher
temperature heat reservoir.
2. Kelvin-Planck Statement :
It is impossible to construct a heat engine operating
on a cycle whose sole effect is the transfer of heat
from a single heat reservoir & its conversion into
equal amount of work.

10. Refrigerator & Heat Pump
10
Refrigerator :
It’s a device operating on a cycle which removes heat
from a low temperature body and rejects it to a body
at high temperature on the expense of external work.
Heat Pump :
If the system delivers heat energy at higher
temperature than that of ambient temperature.
e.g. heater

11. Coefficient of Performance (C.O.P)
11
 The efficiency of refrigerator & heat pump is
expressed in terms of C.O.P.
(C.O.P)refrigerator = Desired Effect / Energy input
= Q2 / W
(C.O.P)heat pump = Desired Effect / Energy input
= Q1 / W
(C.O.P)heat pump - (C.O.P)refrigerator = 1

12. Example
12
 Heat pump is used to maintain house at 23 degree C.
The house is losing heat to outside air through walls
at 60000 kJ/hr. While energy generated in house by
various appliances is 4000 kJ/hr. For a C.O.P of 1.5,
find required power input in kW, supplied to the heat
pump. 6 Marks