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Introduction
The most of general sense of thermodynamics is the study of energy and its relationship to the
properties of matter. All activities in nature involve some interaction between energy and matter.
Thermodynamics is a science that governs the following:
Energy and its transformation
Feasibility of a process involving transformation of energy
Feasibility of a process involving transfer of energy
Equilibrium processes
More specifically, thermodynamics deals with energy conversion, energy exchange and the
direction of exchange.
Areas of Application of Thermodynamics:
All natural processes are governed by the principles of thermodynamics. However, the following
engineering devices are typically designed based on the principles of thermodynamics.
Automotive engines, Turbines, Compressors, Pumps, Fossil and Nuclear Power Plants,
Propulsion systems for the Aircrafts, Separation and Liquefication Plant, Refrigeration, Airconditioning and Heating Devices.
The principles of thermodynamics are summarized in the form of a set of axioms. These axioms
are known as four thermodynamic laws:
The zeroth law, the first law, the second law and the third law.
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The Zeroth Law deals with thermal equilibrium and provides a means for measuring
temperatures.
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The First Law deals with the conservation of energy and introduces the concept of
internal energy.
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The Second Law of thermodynamics provides with the guidelines on the conversion of
internal energy of matter into work. It also introduces the concept of entropy.
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The Third Law of thermodynamics defines the absolute zero of entropy. The entropy of
a pure crystalline substance at absolute zero temperature is zero.
SI Units
SI is the abbreviation of Système International d' Unités. The SI units for mass, length,
time and force are kilogram, meter, second and newton respectively. The unit of length is
meter, m, defined as
1 650 763.73 wavelengths in vacuum of the radiation corresponding to the orange-red
line of the spectrum of Krypton-86. The unit of time is second, s. The second is defined
as the duration of
9 192 631 770 cycles of the radiation associated with a specified transition of the Cesium
133 atom. The unit of mass is kilogram, kg. It is equal to the mass of a particular cylinder
of platinum-iridium alloy kept at the International Bureau of Weights and Measures. The
amount of substance can also be expressed in terms of the mole (mol). One kilomole of a
substance is the amount of that substance in kilograms numerically equal to its molecular
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weight. The number of kilomoles of a substance, n , is obtained by dividing the mass (m)
in kilograms by the moleculare weight (M), in kg/ kmol.
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The unit for temperature is Kelvin, K . One K is the fraction 1/273.16 of the
thermodynamic temperature of the triple point of water. Quite often the Celsius, oC , is
used to express the temperature of a substance.
The SI unit of force, called the newton, N is a secondary unit. The, N , is the force
required to accelerate a mass of 1 kilogram at the rate of 1 meter per (second)2 .
1 N = (1kg) (1m/s2 )= 1kg m/s2
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The smaller or bigger quantities are expressed using the following prefixes
Factor
1012
109
106
103
102
Prefix
tera
giga
mega
kilo
hecto
Symbol
T
G
M
k
h
Factor
10-2
10-3
10-6
10-9
10-12
Prefix
centi
milli
micro
nano
pico
Symbol
c
m
μ
n
p
Pressure
Pressure is the normal force exerted by a system against unit area of the boundary surface.
where δA approaches zero.
The unit for pressure in SI is pacsal, Pa
1 Pa = 1 N/m2
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Two other units are widely used
1 bar = 105 Pa = 100 kPa = 0.1 MPa
and the standard atmosphere, where
1 atm = 101.325 kPa = 1.01325 bar = pressure exerted by a columan of 760 mm of Hg
Energy
Energy is the capacity to exert a force through a distance. In SI, the unit of energy is Newtonmeter, N m or Joule, J.
Power
The rate of energy transfer or storage is called power. The unit of power is watt, W.
1 W = 1 J/s = 1 N m/s and 1 kW = 1000 W.
Apart from these,
the following
units are used for Frequency, Hertz = Hz = s-1
various
parameters of
Electric current, Ampere = A
interest
Electric charge, Coulomb, C = As
Electric potential, Volt = V = W/A
Magnetic flux, Weber, Wb = Vs
Magnetic flux density, Tesla, T = Wb/m2
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