Lect No 02

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. Homogeneous & Heterogeneous Systems
2
Homogeneous system: - if a system consists of
homogeneous matter
throughout in chemical
composition & physical
structure.
e.g. ice, water, superheated steam, tea
Heterogeneous system: - if a system consists of matter
of different chemical
composition & physical
structure.
e.g. mixture of ice & water, mixture of two or more
non-miscible liquids (petrol & water)

3. Pure Substance
3
 It has a homogeneous & invariable chemical
composition even though there is a change of phase.
e.g. liquid water, mixture of water & steam.

4. Dimensions & Units
4
 Any physical quantity can be characterized by
dimensions.
 Dimension is defined as a measurable quantity.
 The magnitudes assigned to the dimensions are
called as units.
 Some basic dimensions such as mass m, length L,
time t , and temperature T are selected as Primary or
Fundamental dimensions.
 Whereas, velocity V, energy E, and volume v , are
selected as Secondary or Derived dimensions.

5. Units
5
 No of unit systems have been developed over the years.
1. English system : (United States Customary System)
It has no apparent systematic numerical base.
Various units are related to each other arbitrarily.
e.g. 12 in = 1 ft, 1 mile = 5280 ft , 4qt = 1 gal, etc.
In U.S. it’s still acceptable.
2. SI system : (International System) (Metric System)
It’s a simple & logical system based on a decimal
relationship between various units.
e.g. mm, cm, m, km, etc
It’s used in most of the nations for scientific &
engineering work.

6. Energy
6
 Energy is capacity to produce an effect, especially that
of change in motion of bodies.
Internal Energy :
Present in a system due to molecular motion,
arrangement of atomic structure, & it’s chemical
composition.
Various types of internal energies are :
a) Chemical Energy : released due to change in chemical
composition.
b) Atomic Energy : released due to change in atomic
structure of matter such as nuclear
fusion or fission.
c) Molecular Internal Energy : energy due to molecular
motion.

7. External Energy
7
a) Potential Energy : energy of position of mass w.r.t.
earth.
b) Kinetic Energy : energy arising due to motion of the
mass.
Total Energy = Internal Energy + External Energy

8. Properties of a System
8
 Any characteristic of a system is called a property.
 Pressure, volume, temperature, mass are few known
properties whereas viscosity, electrical resistivity are
less familiar.
 Properties are of two types,
1. Intensive : independent of the mass of the system.
e.g. temp, pressure, density.
2. Extensive : value depends on the size of the system.
e.g. length, volume, all forms of energies.
 An easy way to determine whether a property is
intensive or extensive is to divide the system into two
equal parts with a an imaginary partition.

9. Properties of a System
9
Each part will have same value
of intensive properties whereas
half value of extensive
properties.

10. Specific Properties
10
 Extensive properties per unit mass are called as
specific properties.
e.g. specific volume = volume/mass
specific total energy = total energy/mass

11. State of a System
11
 A set of properties that completely describes the
condition of the system is known as State.
 At a given state, all properties of a system have fixed
values.
 If the value of even one property changes, the state
will change to a different one.

12. Equilibrium
12
 Thermodynamics deals with the equilibrium states.
 Word equilibrium means state of balance.
 In an equilibrium state there are no unbalanced
potentials within the system.
 Types of equilibrium :
1. Thermal equilibrium – (if temp is same)
2. Mechanical equilibrium – (if press is same)
3. Chemical equilibrium – (if chemical compo is same )

13. Processes & Cycles
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 Any change that system undergoes from one
equilibrium state to another is called a process.
 The series of states through which a system passes
during a process is called the path of the process.
 To describe a process completely, one requires,
- Initial & final states of the process
- Path it follows

14. Processes & Cycles
14
 When a process proceeds in a manner that the
system remains infinitesimally close to an equilibrium
state, it’s called as a quasi-static process.
 It’s a sufficiently slow process. (Allows the system to
adjust itself internally)
 Quasi-static process is an idealized process.
Note : -
We are interested in this process because,
1. Easy to analyze
2. Work – producing devices deliver most work when
they operate on it.

15. Processes & Cycles
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 The prefix iso- is often used to designate a process
for which particular property remains constant.
 An isothermal process, is a process during which
temperature T remains constant.
 Similarly isobaric process (P const) & isometric
process (Specific V Const).