Engineering thermodynamics covers basic concepts including: 1) The continuum approach views matter as a continuous substance rather than discrete atoms, allowing properties to vary continuously through space. 2) Macroscopic and microscopic approaches differ in whether properties are averaged or describe individual molecules. 3) Path functions like work and heat depend on process, while point functions like volume depend only on state. 4) Intensive properties are independent of system size, while extensive properties depend on size.

1. Engineering Thermodynamics
Module 1 - Basic Concepts and First law
Lecture 1 of 3 - Basic Concepts 1
Prepared by
Mr.M.Mani Vannan
Assistant Professor
Department of Mechanical Engineering
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2. Unit I - Basic Concepts and First Law
Basic concepts - concept of continuum, comparison of
microscopic and macroscopic approach. Path and point functions.
Intensive and extensive, total and specific quantities. System and
their types. Thermodynamic Equilibrium State, path and process.
Quasi-static, reversible and irreversible processes. Heat and work
transfer, definition and comparison, sign convention.
Displacement work and other modes of work .P-V diagram.
Zeroth law of thermodynamics – concept of temperature and
thermal equilibrium– relationship between temperature scales –
new temperature scales. First law of thermodynamics –
application to closed and open systems – steady and unsteady
flow processes
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3. Engineering
Engineering is the creative application of science,
mathematical methods, and empirical evidence to the innovation,
design, construction, operation and maintenance of structures,
machines, materials, devices, systems, processes, and
organizations.
The discipline of engineering encompasses a broad range
of more specialized fields of engineering, each with a more
specific emphasis on particular areas of applied mathematics,
applied science, and types of application.
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4. Thermodynamics
Thermodynamics is a branch of physics concerned with
heat and temperature and their relation to other forms of energy
and work.
Thermodynamics applies to a wide variety of topics in
science and engineering, especially physical chemistry, chemical
engineering and mechanical engineering.
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5. Applications of Thermodynamics
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6. Energy
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7. Concept of continuum
1.Matter is made up of atoms that are widely spaced in the gas
phase. Yet it is very convenient to disregard the atomic nature of
a substance and view it as a continuous, homogeneous matter
with no holes, that is, a continuum.
2.The continuum idealization allows us to treat properties as
point functions and to assume the properties vary continually in
space with no jump discontinuities.
3.In continuum approach, fluid properties such as density,
viscosity, thermal conductivity, temperature, etc. can be
expressed as continuous functions of space and time.
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8. Comparison of Microscopic and Macroscopic
Approach
Macroscopic approach Microscopic approach
In this approach , a certain
quantity of matter is considered
without taking into account the
energy occurring at Molecular
level.This is known as classical
Thermodynamics
In this approach, the energy
occurring at the molecular level is
taken into account for analysis.
The values of these energies are
constantly changing with time .
This is known as statistical
Thermodynamics
The analysis of macroscopic
systems requires simple
mathematical formulae
The behaviour of the system is
found by using statistical method
as the number of molecules is very
large.
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9. Cont…
Macroscopic approach Microscopic approach
The values of the properties of
system are their average values.
Example: consider a sample of a
gas in a closed container . The
pressure of the gas is the average
value of the pressure exerted by
millions of individual molecules .
The properties like velocity ,
momentum , impulse , kinetic
energy , force of impact etc ,
which describe the molecule
cannot be easily measured by
instruments . Our senses cannot
feel them .
In order to describe such a system
only a few variables are needed .
Large number of variables are
needed to describe such a system
.So the approach is complicated .
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10. Point and Path Functions
They are introduced to identify the variables of thermodynamics.
Path function: Their magnitudes depend on the path followed
during a process as well as the end states. Work (W), heat (Q) are
path functions.
Process A: WA = 10 kJ
Process b: WB = 7 kJ
Point function: They depend on the
state only, and not on how a system
reaches that state. All properties are
point functions.
Process A: V2 - V1 = 3 m3
Process B: V2 - V1 = 3 m3
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11. Properties
Property: Any characteristic of a system.
Intensive properties: These are independent of the mass of a
system,
Examples: Temperature, Pressure and Density, etc.,
Extensive properties: These are depend on the size of the system.
Examples: Volume, Mass, Heat (Q),Work(W)etc.,
Specific properties: Extensive properties per unit mass.
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12. Pressure
Pressure is the force exerted by a fluid per unit a area.
The actual pressure at a given position is called
the absolute pressure.
Gauge pressure = Absolute pressure - Atmospheric pressure
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13. Cont…
A device measures pressure using a column of liquid is called a
Manometer. The manometer measures the gauge pressure.
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14. Mass (m) and Weight (W)
Mass is a measure of the amount of material an object is made of.
It is measured in kilograms(kg).It is denoted by ‘m’.
Weight is the force of gravity on an object.It is measured in
Newtons (N).It is denoted by ‘W’.
W = m x g
Standard value for acceleration due to gravity, g = 9.8 m/s2
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15. Density(ρ),Specific gravity(s) and specific
volume (v)
Density is defined as mass per unit volume
Specific gravity is the ratio of the density of a substance to the
density of some standard substance at a specific temperature
(usually water at 4°C).It is denoted by ‘s’. It is dimensionless
number.
Specific volume is the reciprocal of density. It is denoted by ‘v’.
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16. Temperature
It is the measure of hotness and coldness in terms of any
arbitrary scales and indicating the direction which energy
spontaneously flows (from a hotter body to a colder one)
A thermometer is any of class of instrument that measures
the temperature. Temperature is the physical magnitude that is
measured by thermometers.
1.Centigrade Temperature Scale (Celsius scale)(ᵒC)
2.Fahrenheit Temperature Scale(ᵒF)
3.Absolute Temperature Scale(K)
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17. Temperature scales
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18. Thank you
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