Module 01
Energy Basics
Energy
Power
Forms of energy
Thermodynamic laws
Entropy
Exergy
Combustion fundamentals
Prof. R. Shanthini
Dec 10, 2011
1
A few suggested references
Shanthini, R., 2009. Thermodynamics for beginners.
Peradeniya: Science Education Unit.
Certain chapters available from:
http://www.rshanthini.com/ThermoBook.htm
MacKay, D.J.C., 2009. Sustainable energy: without
the hot air. Cambridge: UIT Cambridge Ltd.
Available from:
http://www.withouthotair.com/download.html
Prof. R. Shanthini
Dec 10, 2011
2
• What is energy?
– energy is the ability to do work (defined loosely)
Energy is not a ‘thing’ or ‘substance’.
Energy cannot be seen, heard or felt.
Energy is a concept.
Prof. R. Shanthini
Dec 10, 2011
3
• What is energy?
– energy is the ability to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
F is the force pushing the ball
Prof. R. Shanthini
Dec 10, 2011
4
• What is energy?
– energy is the ability to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
F is the force pushing the ball
D
D is the distance over which
the ball is moved
Work = F x D
Prof. R. Shanthini
Dec 10, 2011
5
• What is energy?
– energy is the ability to do work (defined loosely)
Work = Force x Distance
• What is power?
– power is the rate at which work is done
Power = Work / Time
Prof. R. Shanthini
Dec 10, 2011
6
• What is the unit of Energy?
• What is the unit of Work?
• What is the unit of Power?
Prof. R. Shanthini
Dec 10, 2011
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Units for energy / work
joule
1 J (joule)
in SI-system
= 1 N·m = 1 (N/m2) ·m3
= 1 Pa·m3
1 N (newton) = 1 (kg.m/s2)
is the unit of force
1 Pa (pascal) = 1 N/m2
is the unit for pressure
Prof. R. Shanthini
Dec 10, 2011
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SI multiples for joules (W)
Submultiples
Multiples
Value
Symbol
Name
Value
Symbol
Name
10−1 J
dJ
decijoule
101 J
daJ
decajoule
10−2 J
cJ
centijoule
102 J
hJ
hectojoule
10−3 J
mJ
millijoule
103 J
kJ
kilojoule
10−6 J
µJ
microjoule
106 J
MJ
megajoule
10−9 J
nJ
nanojoule
109 J
GJ
gigajoule
10−12 J
pJ
picojoule
1012 J
TJ
terajoule
10−15 J
fJ
femtojoule
1015 J
PJ
petajoule
10−18 J
aJ
attojoule
1018 J
EJ
exajoule
10−21 J
zJ
zeptojoule
1021 J
ZJ
zettajoule
10−24 J
yJ
yoctojoule
1024 J
YJ
yottajoule
Prof. R. Shanthini
Dec 10, 2011
9
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Units for power
watt
1 W (watt)
in SI-system
= 1 J/s
= 1 N.m/s
60 W = 60 J/s
= 60*60 J/m
= 60*60*60 J/h
= 216,000 J/h
= 216 kJ/h
Prof. R. Shanthini
Dec 10, 2011
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SI multiples for watts (J)
Submultiples
Multiples
Value
Symbol
Name
Value
Symbol
Name
10−1 W
dW
deciwatt
101 W
daW
decawatt
10−2 W
cW
centiwatt
102 W
hW
hectowatt
10−3 W
mW
milliwatt
103 W
kW
kilowatt
10−6 W
µW
microwatt
106 W
MW
megawatt
10−9 W
nW
nanowatt
109 W
GW
gigawatt
10−12 W
pW
picowatt
1012 W
TW
terawatt
10−15 W
fW
femtowatt
1015 W
PW
petawatt
10−18 W
aW
attowatt
1018 W
EW
exawatt
10−21 W
zW
zeptowatt
1021 W
ZW
zettawatt
10−24 W
yW
yoctowatt
1024 W
YW
yottawatt
Prof. R. Shanthini
Dec 10, 2011
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Global Energy Consumption
Global Consumption = 15 TW = 15x1012 W
= 250,000,000,000 of 60 W bulbs
= about 35 of 60 W bulbs per person
Prof. R. Shanthini
Dec 10, 2011
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http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Global Energy Consumption
Global Consumption = 15 TW = 15x1012 W
= 250,000,000,000 of 60 W bulbs
= about 35 of 60 W bulbs per person
Prof. R. Shanthini
Dec 10, 2011
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http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
Global Energy Consumption
Global Consumption = 15 TW = 15x1012 J/s = 54x1015 J/h
Prof. R. Shanthini
Dec 10, 2011
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http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)
One joule in everyday life is approximately:
The energy required to raise the temperature of cool, dry air
by one degree Celsius.
A person at rest releases 100 joules of heat every second.
Prof. R. Shanthini
Dec 10, 2011
15
• What is energy?
– energy is the ability to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
• Is heat energy too?
– heat is a form of energy that flows from a
warmer object to a cooler object
– work sometimes gets converted to heat
(think of examples)
– heat sometimes gets converted to work
(think of examples)
Prof. R. Shanthini
Dec 10, 2011
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Units for heat
Joule / Calorie
1 calorie
= the energy needed to raise the temperature
of 1 gram of water by 1oC
= 4.184 J (joules)
= 0.003 964 BTU (British thermal units)
Prof. R. Shanthini
Dec 10, 2011
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For more on energy units and conversions,
Visit
The American Physical Society Site
http://www.aps.org/policy/reports/popa-reports/energy/units.cfm
Prof. R. Shanthini
Dec 10, 2011
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Basic Forms of Energy
•
•
•
•
•
•
•
•
•
Kinetic Energy:
Potential Energy:
Thermal (or Heat) Energy:
Chemical Energy:
Electrical Energy:
Electrochemical Energy:
Sound Energy:
Electromagnetic Energy (light):
Nuclear Energy:
Prof. R. Shanthini
Dec 10, 2011
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Basic Forms of Energy (continued)
• Thermal (or Heat) Energy:
– Consider a hot cup of coffee. The coffee is said to
possess "thermal energy", or "heat energy," which is
really the collective, microscopic, kinetic, and
potential energy of the molecules in the coffee.
• Chemical Energy:
– Consider the ability of your body to do work. The
glucose (blood sugar) in your body is said to have
"chemical energy" because the glucose releases
energy when chemically reacted (combusted) with
oxygen.
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
• Electrical Energy:
– All matter is made up of atoms, and atoms are made
up of smaller particles, called protons, neutrons, and
electrons. Electrons orbit around the center, or
nucleus, of atoms, just like the moon orbits the earth.
The nucleus is made up of neutrons and protons.
– Material, like metals, have certain electrons that are
only loosely attached to their atoms. They can easily
be made to move from one atom to another if an
electric field is applied to them. When those electrons
move among the atoms of matter, a current of
electricity is created.
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
• Electrochemical Energy:
– Consider the energy stored in a battery. Like the
example above involving blood sugar, the battery also
stores energy in a chemical way. But electricity is also
involved, so we say that the battery stores energy
"electro-chemically". Another electron chemical
device is a "fuel-cell".
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
• Sound Energy:
– Sound waves are compression waves associated
with the potential and kinetic energy of air molecules.
When an object moves quickly, for example the head
of drum, it compresses the air nearby, giving that air
potential energy. That air then expands, transforming
the potential energy into kinetic energy (moving air).
The moving air then pushes on and compresses other
air, and so on down the chain.
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
• Electromagnetic Energy (light):
– Consider the energy transmitted to the Earth from the
Sun by light (or by any source of light). Light, which is
also called "electro-magnetic radiation". Why the fancy
term? Because light really can be thought of as
oscillating, coupled electric and magnetic fields that
travel freely through space (without there having to be
charged particles of some kind around).
– It turns out that light may also be thought of as little
packets of energy called photons (that is, as particles,
instead of waves). The word "photon" derives from the
word "photo", which means "light".
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Basic Forms of Energy (continued)
• Nuclear Energy:
– The Sun, nuclear reactors, and the interior of the
Earth, all have "nuclear reactions" as the source of
their energy, that is, reactions that involve changes in
the structure of the nuclei of atoms.
Prof. R. Shanthini
Dec 10, 2011
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Energy is available in different forms.
Energy cannot be created or
destroyed (which is a natural law).
Energy can change from one form to
the other.
Prof. R. Shanthini
Dec 10, 2011
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The study of conversion of energy
is known as
Thermodynamics.
Mostly, it is study of the connection
between heat and work, and the
conversion of one into the other.
Engineering examples: ……………………………………
Prof. R. Shanthini
Dec 10, 2011
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Thermodynamics
is based on fundamentals laws,
which are the natural laws.
These laws have not been proven wrong so far.
These laws will remain as fundamental laws until
someone finds out that they are wrong.
If that happens then we need to redo all
thermodynamics that has been developed so far.
Prof. R. Shanthini
Dec 10, 2011
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First Law of Thermodynamics
Energy is conserved.
That means, energy cannot be created or
destroyed.
However, energy can change from one form
to the other.
Prof. R. Shanthini
Dec 10, 2011
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First Law of Thermodynamics
System
Energy of the system
Qin
E
Wout
Heat energy that entered the system
Work energy that left the system
Prof. R. Shanthini
Dec 10, 2011
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First Law of Thermodynamics
Qin
E
Wout
Efinal - Einitial = Qin – Wout
Prof. R. Shanthini
Dec 10, 2011
ΔE = Qin – Wout
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First Law of Thermodynamics
First law is about the balance of quantities
of energy.
It helps to keep account of what happen to
all forms of energy that are involved in a
process.
Prof. R. Shanthini
Dec 10, 2011
32
Apply First law to Heat Engine
Hot reservoir at TH K
Qin
Heat Engine
Wout
A heat engine is a
mechanical system.
As it cycles through a
repetitive motion, transfers
heat from a high
temperature heat bath to a
low temperature bath, and
performs work on its
environment.
Qout
Cold reservoir at TC K
Prof. R. Shanthini
Dec 10, 2011
Example: Diesel cycle
auto.howstuffworks.com/diesel.htm
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Apply First law to Heat Engine
Hot reservoir at TH K
Qin
Heat Engine
First law gives the
following relationship:
Qin = Wout + Qout
Wout
Qout
Cold reservoir at TC K
Prof. R. Shanthini
Dec 10, 2011
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Hot reservoir at TH K
Qin
Heat Engine
Wout
We like to have an
engine that converts all
heat into work. That is,
we would like to have
Qin = Wout
Is it possible?
Prof. R. Shanthini
Dec 10, 2011
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Second Law of Thermodynamics
Hot reservoir at TH K
Qin
Heat Engine
Wout
Qout
Prof. R. Shanthini
Dec 10, 2011
WHY?
Second law of
thermodynamics says
it is not possible to
convert all heat into
work in an engine.
It says it is necessary
to throw away some
heat to the
environment.
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Second Law of Thermodynamics
Hot reservoir at TH K
Qin
Heat Engine
Wout
Qout
Cold reservoir at TC K
Prof. R. Shanthini
Dec 10, 2011
Maximum possible
thermal efficiency of the
heat engine is
η
=
1
Carnot
-
TC
TH
Since TC can never be
zero,
η
Carnot
<1
37
Second Law of Thermodynamics
Hot reservoir at TH K
Qin
Heat Engine
Wout
Qout
Thermal efficiency of the
heat engine is
W
out
ηth =
Qin
ηth < η
<
1
Carnot
Cold reservoir at TC K
Prof. R. Shanthini
Dec 10, 2011
38
Second Law of Thermodynamics
Hot reservoir at TH K
Qin
Heat Engine
Wout
Qout
Cold reservoir at TC K
Prof. R. Shanthini
Dec 10, 2011
Thermal efficiency of the
heat engine is
W
out
ηth =
Qin
<1
Qin ≠ Wout
Qout ≠ 0
39
Some heat is thrown away.
Entropy
When heat is transformed into work, as in the heat engines,
some heat is always lost to the environment (according to
the Second Law).
This irrevocable loss of some energy to the environment is
associated with an increase of disorder in that system.
Entropy acts as a function of the state of a system - where a
high amount of entropy translates to higher chaos within the
system, and low entropy signals a highly ordered state.
The Second Law tells that the quality of energy is degraded
every time energy is used in any process. This ‘energy
quality’ has been named exergy.
Prof. R. Shanthini
Dec 10, 2011
40
Exergy
The Second Law tells us that the quality of a particular amount
of energy diminishes for each time this energy is used.
This means that the quality of energy in the universe as a
whole is constantly diminishing.
All real processes are irreversible, since the quality of the
energy driving them is lowered for all times.
Prof. R. Shanthini
Dec 10, 2011
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Exergy
The Second Law tells us about the direction of the universe
and all processes, namely towards a decreasing exergy
content of the universe.
Processes that follow this general principle will be preferred.
The usable energy in a system is called exergy, and can be
measured as the total of the free energies in the system.
Unlike energy, exergy can be consumed.
Prof. R. Shanthini
Dec 10, 2011
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The energy of the universe is constant (First Law).
Exergy is constantly consumed (Second Law).
In the end (very long time from now), exergy is used
up in the universe, and no processes can run.
The entropy of a system increases whenever exergy
is lost.
Prof. R. Shanthini
Dec 10, 2011
43
Zeroth Law of Thermodynamics
If
object A is in thermal equilibrium with object C,
and
object B is in thermal equilibrium with object C,
then
object A & B are also in thermal equilibrium.
Thermal Equilibrium = Same temperature
Thermal Equilibrium = No heat flow
Prof. R. Shanthini
Dec 10, 2011
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Third Law of Thermodynamics
It is impossible to reach absolute zero in a
finite number of steps.
Prof. R. Shanthini
Dec 10, 2011
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Combustion Fundamentals
Combustion is a process in which oxidizable materials
such as fossil fuels are oxidized by use of oxygen
(present in the air).
During this process energy is released in the form of heat.
Major combustion product is the global pollutant, carbon
dioxide (CO2), which is a greenhouse gases.
Combustion products also include other local pollutants.
Combustion fundamentals include the nature of the fuels
being burned, the nature of the products formed and the
stoichiometry of the combustion reaction.
Prof. R. Shanthini
Dec 10, 2011
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Combustion (or Fire) Triangle
Prof. R. Shanthini
Dec 10, 2011
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Combustion Engine
The combustion engine is used to power nearly all land
vehicles and many water-based and air-based vehicles.
In an internal combustion engine, a fuel (gasoline for
example) fills a chamber, then it is compressed to heat it up,
and then is ignited by a spark plug, causing a small explosion
which generates work.
Prof. R. Shanthini
Dec 10, 2011
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Combustion Engine
Prof. R. Shanthini
Dec 10, 2011
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Combustion Engine
Prof. R. Shanthini
Dec 10, 2011
50
Combustion Engine
Prof. R. Shanthini
Dec 10, 2011
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http://bancroft.berkeley.edu/Exhibits/physics/images/origins18.jpg
Combustion Engine
Prof. R. Shanthini
Dec 10, 2011
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http://images.yourdictionary.com/images/main/A4gastrb.jpg
Combustion Fundamentals
Stoichiometric (or theoretical) combustion is the ideal
combustion process where fuel is burned completely.
A complete combustion is a process burning
- all the carbon (C) to (CO2),
- all the hydrogen (H) to (H2O) and
- all the sulphur (S) to (SO2).
With unburned components in the exhaust gas, such as C,
H2, CO, the combustion process is incomplete and not
stoichiometric.
Prof. R. Shanthini
Dec 10, 2011
53
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
If an insufficient amount of air is supplied to the burner,
unburned fuel, soot, smoke, and carbon monoxide exhausts
from the boiler - resulting in heat transfer surface fouling,
pollution, lower combustion efficiency, flame instability and a
potential for explosion.
To avoid inefficient and unsafe conditions boilers normally
operate at an excess air level.
Prof. R. Shanthini
Dec 10, 2011
54
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
if air content is higher than the stoichiometric ratio - the
mixture is said to be fuel-lean
if air content is less than the stoichiometric ratio - the
mixture is fuel-rich
Prof. R. Shanthini
Dec 10, 2011
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http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Example - Stoichiometric Combustion of Methane - CH4
CH4 + 2 (O2 + 3.76 N2)
->
CO2 + 2 H2O + 7.52 N2
If more air is supplied some of the air will not be involved in the
reaction. The additional air is termed excess air, but the term
theoretical air may also be used. 200% theoretical air is 100%
excess air.
The chemical equation for methane burned with 25% excess air
can be expressed as
CH4 + 1.25 x 2 (O2 + 3.76 N2) -> CO2 + 2 H2O + 0.5 O2 + 9.4 N2
Prof. R. Shanthini
Dec 10, 2011
56
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html
Combustion Fundamentals
Excess Air and O2 and CO2 in Flue Gas
Approximate values for CO2 and O2 in the flue gas as result of
excess air (for various fuels) are estimated in the table below:
Carbon Dioxide - CO2 - in Flue Gas (% volume)
Oxygen in
Flue Gas
Bituminou Anthracite for all
fuels (%
s Coal
Coal
volume)
Excess
Air
%
Natural
Gas
Propane
Butane
Fuel Oil
0
12
14
15.5
18
20
0
20
10.5
12
13.5
15.5
16.5
3
40
9
10
12
13.5
14
5
60
8
9
10
12
12.5
7.5
80
7
8
9
11
11.5
9
100
6
6
8
9.5
10
10
Prof. R. Shanthini
Dec 10, 2011
57
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html