Lect No 03

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. Thermodynamic Cycle
2
 If a system undergoes two or more processes &
returns to its original state, it’s called as a cycle.
 It forms a closed loop.

3. Thermal Equilibrium
3
 Two bodies A and B are at different temperatures.
 When brought in contact, heat will be transferred,
from body at higher temp. to body at lower temp.
 After sufficient lapse of time there are no change in
state of bodies.
 Such state is known as state of thermal equilibrium.

4. Zeroth Law of Thermodynamics
4
 Formulated in the year 1931 by R. H. Fowler.
 It states that,
“If two bodies are in thermal equilibrium with a third
body, they are also in thermal equilibrium with each
other.”
 It may seems silly that such an obvious fact is one of
the basic laws of thermodynamics..!!
 This law gives us validity of temperature
measurement.
 By replacing third body with a thermometer.
 It was named the zeroth law since it should have
preceded the first & second laws of thermodynamics.

5. Temperature Scale
5
 It enable us to use a common basis of temperature
measurements.
 All temperature scales have states known as freezing
point (ice point) and boiling point (steam point).
 Temp in SI unit is measured in Celsius scale.
 Temp in English system is measured in Fahrenheit
scale.
 Temperatures of Ice & Steam points are :
On Celsius scale (0 & 100 degrees)
On Fahrenheit scale (32 and 212 Fahrenheit)
 These are often referred to as ‘two-point scale’.

6. Temperature Scale
6
 Kelvin Temperature scale : based on only one fixed
point only.
 This is the temperature at which ice, liquid water and
water vapour co-exist.
 It’s known as ‘triple point of water’.
 The value was chosen as 273.16 K.
 This temp scale is known as absolute or
thermodynamic temp scale.

7. Real and Ideal Gas
7
Real Gas : behaviour of all gases at high pressures and
at low temperatures. e.g. air, oxygen,
hydrogen.
Ideal Gas : (Perfect Gas)
Behaviour of real gases at the ideal state is called
ideal or perfect gas.
(Ideal state means state of zero pressure and volume
approaching to infinity)
 Ideal gas follows all gas laws & equations.

8. Ideal Gas Laws
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1. Boyle’s law
2. Charle’s law
3. Gay – lussac law
4. Ideal gas equation
5. Avagadro’s law

9. Point Function & Path Function
9
Point Function :
On graph two co-ordinates define a point & two
properties defines a state.
These properties are called as point function.
e.g. pressure, temp, volume, etc
Path Function :
Certain entities such as heat or work can’t be
located on a graph by a point but represented by
the area enclosed.