Introduction to thermodynamics

Introduction to Engineering Thermodynamics
Dr. Rohit Singh Lather, Associate Professor
Science blasts many doubts, foresees what is not obvious
It is the eye of everyone, one who hasn't got it, is like blind ||

Thermodynamics – A Philosophy
• Thermodynamics is the science that primarily deals with energy
• In its origins, thermodynamics was the study of engines
• First century AD - Heron of Alexandria, first recognized thermal engineer
• 1593 - Galileo develops a water thermoscope
AeolipileHero of Alexandria
Reaction engine
First recorded steam engine
thermoscope
Source: www.wikipedia.com

Aristotle
“Nature abhors a vacuum”
Empty or unfilled spaces are unnatural as they go against
the laws of nature and physics
Otto von Guericke
Designed and built the world's first vacuum pump
• 1650 - Otto von Guericke designed and built the world's first vacuum pump and created the
world's first ever vacuum known as the Magdeburg hemispheres, a precursor of the engine
Magdeburg hemispheres : Large copper hemispheres, with mating rims, were used to
demonstrate the power of atmospheric pressure. The rims were sealed with grease and the air
was pumped out
Source: www.wikipedia.com

Source: www.wikipedia.com; www.google.com

• 1656 - English scientist Robert Hooke, built an air pump
- Using this pump, Boyle and Hooke noticed a correlation between pressure, temperature,
and volume
(Boyles’s Law - pressure and volume are inversely proportional)
• 1679 – Denis Papin conceived of the idea of a piston and a cylinder engine after watching steam
release valve of steam digester rhythmically move up and kept the machine from
exploding, which was a closed vessel with a tightly
Steam DigesterAir Pump

• 1697 – Thomas Savery an engineer built the first engine (based on Papin's designs)
• 1700’s – Industrial Revolution
• 1712 - Thomas Newcomen built another engine
- Early engines were crude and inefficient, but attracted the attention of the leading scientists of the time
• 1760s - Joseph Black Professor at the University of Glasgow develops calorimetry
- Developed the fundamental concepts of heat capacity and latent heat
- Joseph Black with James Watt (employed as an instrument maker), performed
experiments together, but it was Watt who conceived the idea of the external
condenser which resulted in a large increase in steam engine efficiency
• 1780s - James Watt improves the steam engine
• 1824 – Sadi Carnot, the "father of thermodynamics", published ”Reflections on the motive power
of fire”, a discourse on heat, power, energy and engine efficiency
- The paper outlined the basic energetic relations between the Carnot engine, the Carnot
cycle and motive power. Discusses idealized heat engines
- Marked the start of thermodynamics as a modern science

• 1849 -Lord Kelvin coined the word “thermodynamics”
• 1850 - Rudolf Clausius came up with the term “entropy”
• 1850s - The first and second laws of thermodynamics emerged simultaneously in the, primarily out
of the works of William Rankine, Rudolf Clausius, and William Thomson (Lord Kelvin)
• 1859 – William Rankine - first thermodynamic textbook
• 1871 - James Maxwell formulated the Statistical Mechanical branch of thermodynamics
• 1875 - Ludwig Boltzmann precisely connected entropy and molecular motion

Thermodynamics and its branches
• Description of the states of thermodynamical systems at near-equilibrium, using macroscopic, empirical
properties directly measurable in the laboratory
• Deals with exchanges of energy, work and heat based on the laws of thermodynamics
• Emerged with the development of atomic and molecular theories
• Relates the microscopic properties of individual atoms and molecules to the macroscopic, bulk properties of
materials that can be observed on the human scale, thereby explaining thermodynamics at the microscopic
level
• Equilibrium thermodynamics is the systematic study of transformations of matter and energy in systems as
they approach equilibrium
• Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not
in thermodynamic equilibrium
• Study of the interrelation of energy with chemical reactions or with a physical change of state within the
confines of the laws of thermodynamics
Classical Thermodynamics
Statistical Mechanics (Statistical Thermodynamics)
Chemical Thermodynamics
Treatment of equilibrium

Applications of Thermodynamics
Power plants
The human body
Air-conditioning
systems
Airplanes
Car radiators
Refrigeration systems
Source: Yunus A. Cengel and Michael A. Boles Thermodynamics: An Engineering Approach, McGraw Hill, 8th Edition

Introduction
We introduce here classical thermodynamics
• “Thermodynamics” is of Greek origin, and is translated as the combination of therme: heat and
dynamis: power
• Thermodynamics is based on empirical observation
• The word “thermo-dynamic,” used first by Lord Kelvin
• Study of the relationship between heat, work, and other forms of
energy
• Describes what is possible and what is impossible during energy
conversion processes
• Describes the "direction" of a process
• Studies the effects of temperature on physical systems at the
macroscopic scale
• All of these things accurately describe thermodynamics
• Thermodynamics is the study of energy conversion, most typically
through terms of heat and work
Sir William Thomson a.k.a
Lord Kelvin (1824 – 1907)Source: www.britannica.com/biography/William-Thomson-Baron-Kelvin

Forms of Energy
Energy
Macroscopic Microscopic
Kinetic Potential
Sensible
(translational + rotational + vibrational)
Latent
(inter molecular phase change)
Chemical
(Atomic Bonds)
Atomic
(bonds within nucleolus of atoms)
Summation of all the microscopic energies is called Internal Energy
E= U+KE+PE (kJ)
Low Grade High GradeHeat Work

Macroscopic vs. Microscopic
• The behavior of a system may be investigated from either a microscopic or macroscopic point of
view
Statistical Approach
Macroscopic Approach
• On the basis of statistical considerations and probability
theory
• we deal with average values for all particles under
consideration
- Reducing the number of variables to a few that can be
handled
• Concerned with the gross or average effects of many
molecules
• These effects can be perceived by our senses and measured
by instruments
Understanding microscopic point of view
Cube with
1m3Air
2.4 × 1025
Molecules
Due to collision the position velocity and energy
changes for each molecules
The behavior of the gas is described by
summing up the behavior of each molecule
To specify position and velocity,
we need three coordinates x, y and z
1.4 × 1026 equations

Container
Gas exerts pressure
on the walls due to
change in momentum of
the molecules as they
collide with the wall
• From a macroscopic point of view, we are concerned not with the action of the individual
molecules but with the time-averaged force on a given area, which can be measured by a
pressure gauge
• Macroscopic observations are completely independent of our assumptions regarding the nature
of matter
• We are always concerned with volumes that are very large compared to molecular dimensions
and, therefore, with systems that contain many molecules
• Because we are not concerned with the behavior of individual molecules, we can treat the
substance as being continuous, disregarding the action of individual molecules

Continuum
• The limit in which discrete changes from molecule to molecule can be
ignored and distances and times over which we are concerned are
much larger than those of the molecular scale
• This will enable the use of calculus in our continuum thermodynamics

Thermodynamic
System
A quantity of fixed
mass under
investigation
Universe
Combination of system and surroundings
Surroundings
Everything external to the system
System Boundary
Interface separating system and surroundings (fixed or moving)
Heat In
Work Out
Definitions

Open System
a system in which mass
crosses boundary, energy
transfer in and out
Closed System
a system with fixed
mass, no mass transfer,
energy may transfer in
and out
Isolated System
A system in which there
are no interactions
between system and
surroundings, no mass
and energy transfer

system → fixed mass
constant mass, but possible variable volume

Control Volume
Control Volume
• Control Volume: fixed volume over which mass can pass in and out of its boundary
• The mass within a control volume may or may not be constant
- If there is fluid flow in and out there may or may not be accumulation of mass within the
control volume
control volume → potentially variable mass, open

A control volume can involve fixed, moving, real and imaginary boundaries

Thermodynamic Properties
If you can’t measure it, you can’t improve it – Lord Kelvin
Thermodynamic properties can be divided into two
general classes, intensive and extensive properties
When all the properties of a system have definite values,
the system is said to exist at a definite state
Property - A property of a system is any observable (macroscopic) characteristics of the
system. The properties we shall deal with are measurable in terms of numbers and units of
measurements (eg. Pressure, density, temperature etc.)
Extensive Property
The value of an extensive property
varies directly with the mass, examples
are: Mass and total volume
Intensive Property
Intensive property is independent
of the amount of mass, examples
are: Temperature, pressure,
specific volume, and density
Thus, if a quantity of matter in a given state is divided into two equal parts, each part will have the
same value of intensive property as the original and half the value of the extensive property

• An Extensive variable depends on the size
of the system.
• Examples of extensive variables are internal
energy, enthalpy, heat capacity at constant
pressure, heat capacity at constant volume,
entropy, Helmholtz energy, Gibbs energy,
volume
• For a system consisting of several parts, an
extensive property of the ensemble of the
parts is the sum of the corresponding
extensive property of each of the parts
• Extensive properties of a system containing
a pure species are proportional to the
number of moles of the species present
• An Intensive variable has a uniform value in
different subdivisions of a system
• Examples of intensive variables are pressure,
temperature, identical in all points of the
system, Molar variables or partial molar
variables, specific mass, mole fractions, molar
heat capacity at constant pressure, have the
same values in all points of one phase of the
system.
• They may differ from one phase† to another.

State
• State is the condition of the system at an instance of time as described or measured by the
properties
OR
Each unique condition of a system is called a state
• At a particular state, all properties have fixed values
State 1 State 2
P1T1V1 P2T2V2

State functions the endpoints of your definite integral are all that matter:
you could parameterize any path you want between the endpoints and the
resulting integral is the same
Property and Non Property
An infinitesimal change in a state function is represented by an exact differential

Change of a State Variable as the Result of a
Thermodynamic Process
General Process
For a state variable, X , (XF – XI) is
independent of the path used for the
process. The intermediate states of the
system are irrelevant
Cyclic Process
Consider a thermodynamic change of a
system to some intermediate state via
path 1. Then along path 2, bring the
system back to its initial state. This
process is a cyclic process
I F I Int.
(XF – XI)path 1 = (XF – XI)path 2
Path 1
Path 2
Path 1
Path 2
The change of X is zero for a cyclic process
Intermediate StateInitial StateFinal StateInitial State
Source: Introductory Thermodynamics,Pierre Infelta Swiss Federal Institute of Technology Lausanne,
Switzerland

• Example of a cyclic process: the initial state and final
state is identical
• There is no volume change
• The change of any state variable is zero for any
cyclic process
• A variable X is a state variable (or state function) if its
change for a cyclic process is zero
• X is also a state variable if its change for a general
process depends only on the initial and final states of
the system and not on the way the change is achieved.
• The differential form dX is then called an exact
differential
• The line integral of an exact differential is
independent of the path of integration
1
2
3
x
Y
Source: Introductory Thermodynamics,Pierre Infelta Swiss Federal Institute of Technology Lausanne, Switzerland

Processes and Cycles
• Change of State: implies one or more properties of the system has changed
- the changes are slow relative to the underlying molecular time scales
• Process: a succession of changes of state
- We assume our processes are all sufficiently slow such that each stage of the
process is near equilibrium
- isothermal: constant temperature
- isobaric: constant pressure
- isochoric: constant volume
• Path: The succession of states passed through during a change of state is called path of the
change of state
• Cycle: series of processes which returns to the original state. (A thermodynamic cycle is
defined as a series of state changes such that the final state is identical with the initial state)
- The cycle is a thermodynamic “round trip.”

Volume
Pressure
a
b
1
2
Cycle
1-2-1
Process
a - b
Cycle
a series of state changes such that the
final state is identical with the initial state
Reversible Process
When a system undergoes changes in such a manner
it is able to retain its original condition by following
the same thermodynamic path in the reverse
direction, it is then said to have undergone a
reversible process
Irreversible process
When the system is unable to reach the original
condition by retracing its path or attain the
original conditions along other thermodynamic
paths, then the process is said to be an
irreversible process
A process becomes irreversible due to the friction
Process
Change of state, when the path is
completely specified
A process is completely specified by the end states,
the path, and the interactions that take place at
the boundary

Quasi-Static Process
• Arbitrarily slow process such that system always stays stays arbitrarily close to thermodynamic
equilibrium
• Infinite slowness is the characteristics of a quasi-static process
• It is a succession of equilibrium states
• A quasi-static process is also reversible process
Dots indicate
equilibrium states
Pressure
1
2
Volume
Every state passed through by the
system will be an equilibrium state
Such a process is locus of all the
equilibrium points passed through by
the system
System Boundary
Piston
Weight
Final State
Initial State
Multiple
Weights
Final State
Initial State
Piston
dv
dp

Thermodynamic Equilibrium
• Thermodynamic Equilibrium: state in which no spontaneous changes (macroscopic properties) are
observed with respect to time
- We actually never totally achieve equilibrium, we only approximate it
- It takes infinite time to achieve final equilibrium
Non-equilibrium thermodynamics: branch of thermodynamics which considers systems
often far from equilibrium and the time-dynamics of their path to equilibrium
Chemical Equilibrium
Characterized by equal
chemical potentials
Thermal Equilibrium
Characterized by
equal temperature
Mechanical Equilibrium
Characterized by equal
forces (pressure)

Introduction to thermodynamics

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Introduction to thermodynamics