This document provides an overview of thermodynamic concepts including: 1) Thermodynamic cycles which occur when a system returns to its original state after undergoing two or more processes, forming a closed loop. 2) Thermal equilibrium which is reached when two bodies in contact transfer heat until their temperatures equalize and no further changes occur. 3) The zeroth law of thermodynamics which states that if two bodies are in equilibrium with a third body, they are also in equilibrium with each other, establishing the validity of temperature measurement. 4) Common temperature scales including Celsius, Fahrenheit, and Kelvin, with their defining points of ice, steam, and the triple point of water.

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
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 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
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 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
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 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
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 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
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 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
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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
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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.