UNIT
Thermodynamic
Structure
1.1 Introduction
1.2 Thermo dynamics
1.3 Types of System
1.4 Properties of Thermodynamics
1.5 Pressure
1.6 Volume
1.7 Temperature
1.8 Enthalpy
1.9 Atmospheric Pressure
1.10 Internal Energy
1.11 Specific heat
1.12 Summary
Learning Objectives
After studying this chapter you will be able to know
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• Meaning of System in Thermodynamics.
• Types in thermodynamics Systems.
• About Pressure, Volume, Temperature, Enthalpy, atmospheric pressure,
Internal energy, Specific heat
1.1 Introduction
Thermodynamics is branch of science that deals transformation of energy
from one form to another.
Thermodynamics deals with the behaviour of gases and vapours when
subjected to variations of temperature and pressure and relationship between
heat energy and mechanical energy.
1.2 Thermodynamics System
A system in a prescribed region of space with definite boundary which
contains quantity of matter whose behaviour is to be studied
Fig. 1.1
Boundary : The actual envelope enclosing the system is the boundary.
Surrounding : Everything outside the system which has direct bearing on
its behaviour is known as surrounding.
1.3 Types of Thermodynamics Systems
There are three types of systems
1. Closed System.
2. Open System.
3. Isolated System.
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Closed Systems : In closed system transfer of energy takes place i.e
work and heat. But transfer of mass does not takes place.
Example 1. Compression of gas in a piston cylinder 2. Refrigerator ,
3 heating of water in a chemical vessel.
Open System : In Open System both mass and energy transferred between
the system and surroundings.
Example: 1.Gas Turbine 2. Boiler delivering system 3 .Steam turbine.
Isolated System : An Isolated system cannot exchange both energy and
mass with its surroundings. System and surrounding together form a universe.
1.4 Properties of Thermodynamics Systems
The exact condition of a substance is called its state and variable. which
determine the state are known as its properties. The principal properties are
pressure, Volume, Temperature, Internal energy, enthalpy and entropy. The
fundamental properties are pressure, volume an temperature.
There are two types of properties.
1. Intensive Properties.
2. Extensive Properties.
Intensive Properties. These properties do not depend on the mass of the
system. Example: Temperature and pressure.
Extensive Properties. These properties depend on its mass of thesystem.
Example: Volume.
Definitions of Properties
1.5 Pressure
Pressure is a force applied over a unit area. In MKS system. the unit of
area is the square meter and the pressure is measured in kilograms per square
meter {kg/m2}
Engineers measure pressure in kilograms per square centimetres {kg/cm2}
In SI system the unit for pressure is the force one newton {N} Acting on a
square meter area {N/M2}
1.6 Volume (V)
Volume is defined as the space which the substance occupies and it is
measured in cubic meter (m3)
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1.7 Temperature
The temperature of a substance may be define as measure of hotness or
degree of coldness, of a body. A body is said to be hot when it has a relatively
high temperature, it is said to be cold when it has relatively low temperature
.ordinary temperatures are measured by thermometers. Very high temperatures
are measured by pyrometers it is measured in oC, oK, oF.
1.8 Enthalpy
It is also called as total heat. Enthalpy is an energy term and is denoted by
H therefore H=U+PV
Where U is the internal energy, P is absolute pressure, and V is the volume.
1.9 Atmospheric Pressure
The Atmospheric Surroundings the earth exerts a pressure in its surface,
Equivalent to its weight of air over a unit area of the earth’s surface is called
Atmospheric Pressure. The pressure of its atmospheric is recorded by a barmeter.
1.10 Internal Energy
Internal Energy of a substance may be defined as the algebraic sum of
internal kinetic energy and the internal potential energy of its molecules.
If the temperature of a gas increased the molecular activity increases, so
the temperature decreased the molecular activity decreased, so the internal energy
increases if the temperature is decreased then the molecular activity decreased.
1.11Specific Heat
The Specific Heat of a substance may be defined as the amount of heat
that must be supplied to the substance to raise the temperature of unit mass of
the substance through one degree
Specific Heat K=dq/ dT
Where dq is heat supplied per unit mass. dT is change in its temperature.
Test Your Understanding - I
State with reasons whether the following statements are TRUE or FALSE
i) Thermodynamics is an science which deals with the
relations among heat, work and properties of system.
ii) In Open system mass flows out of the system.
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iii) The properties which do not depends on the mass of the system are
known as Extensive Properties.
iv) The properties which depends on the mass of the system are known as
Intensive Properties.
v) If temperature increases internal energy decreased.
Terms Introduced in the Chapter
1. Systems
2. Surroundings
3. Boundary
4. Enthalpy .
5. Atmospheric Pressure .
1.12 Summary
1. Thermodynamics is an science which deals with the relations among
heat, work and properties of systems which are in equilibrium.
2. A system is a finite quantity of matter or a prescribed region of
space.
3. If temperature increases internal energy increases.
4. The total heat of substance is known as enthalpy.
Questions for Practice
1. Explain the terms system surrounding and boundry?
2. Explain the closed systems?
3. Explain the open systems?
4. Explain the isolated system?
5. Explain the terms pressure and temperature?
6. Explain the terms enthalpy and internal energy?
7. Explain the intensive properties?
8. Explain the extensive properties?