Basic Concepts of thermodynamics,

1. Subject:- Thermal Engineering (ME3403)
Topic :- 1.1. Basic Concepts (Concept of pure substance, types of systems , properties of
systems, Extensive and Intensive properties, flow and non-flow processes, specific volume,
temperature, density, pressure. Processes and cycles. Gauge pressure, Absolute Pressure,
Atmospheric pressure, Vacuum pressure and their relation. Simple numericals.)

2. Concept of pure substance:-
Pure substance is defined as, “the substance which remains homogeneous and
its chemical composition does not change, even though, it undergoes change of
phase”.
Example:-
1) Liquid or water

3. Systems:-
Thermodynamic system is defined as “a region in space, upon which, attention
is focused for understanding the concept of transfer and conversion of
energies like heat and work”
Surrounding:-
Everything outside the system is called as surrounding.
Boundary:-
Boundary is defined as the envelope, enclosing the system.
It separates the system from surrounding.
Universe:-
The system and surrounding together is called as universe.

4. Types of Systems:-
Closed system:-
When there is transfer of energy, i.e. heat and work, across the boundaries, such
system is called as the closed system.
Examples:-
1) Piston in a cylinder.
2) Thermal Power plant.
Open System:-
When there is transfer of mass and energy across the boundaries, such system is
called as
the open system.
Examples:-
1) Gas turbine power plant.
2) Air compressor.

5. Isolated System:-
When there is no transfer of mass and energy across the boundaries, such
system is called as
the isolated system.
Examples:-
1) Gas enclosed in the insulated container.
2) Thermos.

7. S.N
.
Comparative
Point
Open System Closed System
01. Mass
Mass of the system
does not remain
constant.
Mass of the system
remains constant.
02. Concept
It can be explained with
the concept of control
volume and control
surface
It can be explained with
the concept of
boundaries.
03.
Mass and
energy
transfer
Mass and energy may
transfer across control
volume
Only energy transfer
take place across the
boundary of the system
Properties of Systems:-

8. Thermodynamic properties
Thermodynamic properties are the characteristics (identifiable and
observable) of a system by which it can be specified.
For example mass, volume, temperature.
Thermodynamic properties can be divided into two groups : Extensive
properties and intensive properties

9. Extensive Thermodynamic Property
Extensive properties are those properties which depend on the extent of the
system. That means extensive properties are directly related (directly
proportional) to the mass.
Examples of extensive properties: volume, internal energy, mass, enthalpy,
entropy etc.

10. Intensive Thermodynamic Properties
Intensive properties are those properties of the system which do not depend
on the extent of the system. That means intensive properties are not related
to the mass.
Examples of intensive properties:

11. FLOW AND NON FLOW PROCESS
Non Flow process
The processes occurring in closed system which do not permit the transfer of
mass to and from the system, are known as flow processes.
It may be noted that in non flow processes, the energy crosses the system
boundary in the form of heat and work, but there is no mass flow in to or out
of the system.

12. FUNDAMENTAL OF THERMODYNAMICS
Flow process:-
1.The processes occurring in open system which permits the transfer of mass
to and from the system. Are known as flow processes. O It may be noted that
in a flow process, the mass
2.enters the system and leaves after enhancing energy.
3.The flow processes may be steady flow or non steady flow processes.
4.Steady flow processes e.g. Flow through nozzles, turbines compressors etc.
5.Non steady flow processes are filling or
evacuation of vessels.

13. Specific Volume:-
Specific volume is the volume occupied by one kg of gas. It is denoted by
Vs.
It is measured in m3/kg.
Mathematically:-
Vs= Volume
Mass
Density:-
Density is the ratio of mass to the volume.
It is measured by p. It is also called as mass density.
Mathematically:-
p= Mass
Volume
Unit: kg/m3

14. Temperature:-
Temperature is a thermodynamic property, which shows the degree of
hotness or heat intensity of the body. It is measured with the help of
thermometer, thermocouple, radiation pyrometer etc. In degree Celsius,
Kelvin or degree farenhite(i.e. °C, °K or °F).
Conversion of units:
K= ‘t’ °C + 273
°F = 9‘t’ °C + 32
5
For example, for temperature 25°C, its conversion is,
(1) Kelvin 25°C + 273 = 298 K
(2) Farenhite 25°C + 32 = 77°F

15. Guage pressure:-
Gauge pressure is defined as the pressure which is measured with the help of a
pressure measuring instrument, in which the atmospheric pressure is taken as
datum. The atmospheric pressure on the scale is marked as zero.
Absolute pressure:-
Absolute pressure is defined as the pressure which is measured with reference
to absolute vacuum pressure.
Vaccum pressure:-
Vacuum pressure is defined as the pressure below the atmospheric pressure.
Atmospheric pressure:-
Atmospheric pressure, also known as barometric pressure, is the pressure
within the atmosphere of Earth. The standard atmosphere is a unit of pressure
defined as 101,325 Pa, which is equivalent to 760 mm Hg, 29.9212 inches Hg,
or 14.696 psi.

16. Relationship between pressures

17. ThankYou