Transcript Slide 1

Module 01
Energy Basics
Energy
Power
Forms of energy
Thermodynamic laws
Entropy / Exergy
Combustion fundamentals
Prof. R. Shanthini
Dec 29, 2012
1
A few suggested references
Shanthini, R., 2009. Thermodynamics for beginners.
Peradeniya: Science Education Unit.
All chapters available at:
http://www.rshanthini.com/ThermoBook.htm
MacKay, D.J.C., 2009. Sustainable energy: without
the hot air. Cambridge: UIT Cambridge Ltd.
Available at:
http://www.withouthotair.com/download.html
(also the kindle version)
Prof. R. Shanthini
Dec 29, 2012
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• What is energy?
– energy is the potential 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 29, 2012
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• What is energy?
– energy is the potential to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
Prof. R. Shanthini
Dec 29, 2012
F is the force pushing the ball
4
• What is energy?
– energy is the potential to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
Prof. R. Shanthini
Dec 29, 2012
F is the force pushing the ball
5
• What is energy?
– energy is the potential to do work (defined loosely)
• What is work?
– force exerted over a distance (scientific definition)
F
F is the force pushing the ball
D is the distance over which
the ball is moved
D
Work = F x D
Prof. R. Shanthini
Dec 29, 2012
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• What is energy?
– energy is the potential to do work (defined loosely)
Work = Force x Distance
• What is force?
– mechanical force (impact of one moving object on another)
– gravitational force (force acting between distant masses)
– electrical force (attraction and repulsion of changed particles)
– magnetic force (attraction and repulsion of magnetic objects)
– and more………
Prof. R. Shanthini
Dec 29, 2012
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• What is energy?
– energy is the potential to do work (defined loosely)
• Where else can one find the potential to do work?
– in a moving particle (as kinetic energy)
– in a mass (Einstein’s contribution: E = mc2)
– in a body at a certain temperature (as internal energy)
– in a chemical compound (as chemical energy)
– in a nuclei (as nuclear energy)
– and more…..
Prof. R. Shanthini
Dec 29, 2012
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• What is energy?
– energy is the potential to do work (defined loosely)
Work = Force x Distance
• What is power?
– power is the rate at which work is done
Power = Work / Time
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• What is the unit of Energy?
• What is the unit of Work?
• What is the unit of Power?
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Dec 29, 2012
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Units for energy / work
joule
1 J (joule)
in SI-system
= 1 N·m
1 N (newton) = 1 (kg.m/s2)
is the unit of force
1 Pa (pascal) = 1 N/m2
is the unit for pressure
J
Prof. R. Shanthini
Dec 29, 2012
=
N·m
=
(N/m2) · m3
=
Pa·m3
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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 J of heat every second.
Prof. R. Shanthini
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SI multiples for joules (J)
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
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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 x 60 J/m
= 60 x 60 x 60 J/h
= 216,000 J/h
= 216 kJ/h
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A person at rest releases 100 J of heat every second.
It is equivalent to100 W
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SI multiples for watts (W)
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
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Dec 29, 2012
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Global Energy Consumption
Global primary energy consumption in 2011
= 12274.6 million tonnes of oil equivalent per year
1 tonne of oil equivalent (toe) is the
rounded-off amount of energy that
would be produced by burning one
tonne ( = metric ton = 1000 kg) of
crude oil.
One tonne of oil equivalent = 41.9 gigajoules
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BP Statistical Review of World Energy June 2012 (bp.com/statisticalreview)
Global Energy Consumption
Global primary energy consumption in 2011
= 12274.6 million tonnes of oil equivalent per year
≈ 12274.6 x 41.9 million gigajoules per year
≈ 515533 million gigajoules (GJ) per year
≈ 515533 petajoules (PJ) per year
[= 515.5 exajoules (EJ) per year]
≈ 1412.42 PJ per day
≈ 58.85 PJ per hour
≈ 0.98085 PJ per min
≈ 980.85 terajoules (TJ) per min
≈ 16.3 TJ per sec
≈ 16.3 terawatts (TW)
Prof. R. Shanthini
Dec 29, 2012
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BP Statistical Review of World Energy June 2012 (bp.com/statisticalreview)
Global Energy Consumption
Global Consumption ≈ 16.3 TW = 16.3 x1012 W
≈ 271,666,666,666 of 60 W bulbs
World population, for mid-year 2011, is estimated at
7,021,836,029.
Global Consumption ≈ 38.7 of 60 W bulbs per person in 2011
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Global Energy Consumption (in TW)
17
15
13
11
9
7
5
1965
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1975
1985
1995
2005
2015
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• 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)
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Dec 29, 2012
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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
= 4.1868 J (joules)
= 0.003 964 BTU (British thermal units)
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Dec 29, 2012
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Energy conversion from one unit to another
1 calorie
= 4.1868000 J
1 kiloWatt hour (kWh)
= 3600000 J = 3600 kJ = 3.6 MJ
1 British Thermal Unit (BTU)
= 1055.06 J
1 ton oil equivalent (toe)
= 41.9 x 109 J = 41.9 GJ
1 ton coal equivalent
= 29.3 x 109 J = 29.3 GJ
1 ton oil equivalent (toe)
= 1 / 7.33 barrel of oil
1 cubic meter of natural gas
= 37.0 x 106 J = 37.0 MJ
1 horsepower
= 746 W = 0.746 kW
Prof. R. Shanthini
Dec 29, 2012
1 kWh is the energy used by a 1 kW
equipment for a duration of 1 hour.
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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 29, 2012
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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:
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Basic Forms of Energy (continued)
• Kinetic Energy:
• Potential Energy:
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Hydropower
Hydroelectricgeneration
power generation
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Hydroelectric power generation
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http://ga.water.usgs.gov/edu/wuhy.html
Hydroelectric power generation
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Hydroelectric power generation
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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 29, 2012
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
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
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Source: http://euclidstube.com/poe/Thermodynamics.ppt
Steam turbine power generation
Prof. R. Shanthini
Dec 29, 2012
Warning: not a technically complete diagram
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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 29, 2012
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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.
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Dec 29, 2012
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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
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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.
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Dec 29, 2012
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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.
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Dec 29, 2012
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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: ……………………………………
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Dec 29, 2012
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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.
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Dec 29, 2012
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First Law of Thermodynamics
Energy is always conserved.
That means, energy cannot be created or
destroyed.
However, energy can change from one form
to the other.
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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
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Dec 29, 2012
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First Law of Thermodynamics
Qin
E
Wout
Efinal - Einitial = Qin – Wout
Prof. R. Shanthini
Dec 29, 2012
ΔE = Qin – Wout
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First Law of Thermodynamics
Qin
E
Wout
ΔE = Qin – Wout = 0
for a system at steady state
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Dec 29, 2012
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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 29, 2012
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Apply First Law to a Heat Engine
Turbine
Steam Turbine
Wout
Condenser
Boiler
Warm water
Qout
Pump
Cold water
Qin
Turbine gives work to the generator to make electricity
Flame gives heat to convert water to steam.
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Dec 29, 2012
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Apply First Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
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.
Hot reservoir at TH K
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Dec 29, 2012
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Apply First Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
First law gives the
following relationship:
Qin = Wout + Qout
Qin
Hot reservoir at TH K
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Dec 29, 2012
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Apply First Law to Heat Engine
Turbine
Steam Turbine
Wout
Condenser
Boiler
Warm water
Qout
Pump
Cold water
Qin
Prof. R. Shanthini
Dec 29, 2012
Hot reservoir is the flame at temperature TH K
Cold reservoir is the cold water at temperature 49
TC K
Apply First Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
We like to have an
engine that converts
all heat into work.
That is, we would like
to have
Qin = Wout
Hot reservoir at TH K
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Dec 29, 2012
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Apply First Law to Heat Engine
We like to have an
engine that converts
all heat into work.
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
That is, we would like
to have
Qin = Wout
Is that possible?
51
Apply Second Law to Heat Engine
Qout
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
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.
WHY?
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Carnot efficiency
Cold reservoir at TC K
Qout
Heat Engine
Wout
Maximum possible
thermal efficiency of a
heat engine is
η
=
1
Carnot
-
TC
TH
Qin
Hot reservoir at TH K
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Dec 29, 2012
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Nicolas Léonard Sadi Carnot
(1796-1832)
- Write the book Reflections on the Motive Power of
Fire in 1824
- Laid the foundations for the second law of
thermodynamics.
- Introduced concepts such as
Carnot efficiency
Carnot theorem
Carnot heat engine
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Dec 29, 2012
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Apply Second Law to a Heat Engine
Steam Turbine
Turbine
Wout
Condenser
Boiler
Warm water
Qout
Pump
Cold water
Qin
TH = 1000 K
TC = 300 K
Prof. R. Shanthini
Dec 29, 2012
η
=
1
Carnot
-
TC
TH
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Apply Second Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
Maximum possible
thermal efficiency of a
heat engine is
η
=
1
Carnot
-
TC
TH
TC can never be zero.
WHY?
56
Third Law of Thermodynamics
It is impossible to reach absolute zero in a
finite number of steps.
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Apply Second Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
Maximum possible
thermal efficiency of a
heat engine is
η
=
1
Carnot
-
TC
TH
Since TC can never be
zero,
η
Carnot
<1
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Apply Second Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
Thermal efficiency of the
heat engine is
W
out
ηth =
Qin
ηth < η
<
1
Carnot
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Apply Second Law to Heat Engine
Cold reservoir at TC K
Qout
Heat Engine
Wout
Qin
Hot reservoir at TH K
Prof. R. Shanthini
Dec 29, 2012
Thermal efficiency of the
heat engine is
W
out
ηth =
Qin
<1
Qin ≠ Wout
Qout ≠ 0
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Some heat is thrown away.
Apply Second Law to a Heat Engine
Turbine
Steam Turbine
Wout
Condenser
Boiler
Warm water
Qout
Pump
Cold water
Qin
TH = 1000 K
TC = 300 K
Prof. R. Shanthini
Dec 29, 2012
Qin = 5000 kJ/s
ηCarnot = ?
Qout = ? kW
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Exergy (Available Energy)
Exergy is also called Availability or Work Potential.
Exergy is the maximum useful work that can be obtained from
a system (at a given state in a given environment)
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Exergy (Available Energy)
Surroundings: outside the system boundaries
Environment: the area of the surroundings not affected by
the process at any point
(For example, if you have a hot turbine, the air next to the
turbine is warm. The environment is the area of the
surroundings far enough away that the temperature isn’t
affected.)
Dead State: when a system is in thermodynamic equilibrium
with the environment, no more work can be done
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Dec 29, 2012
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Zeroth Law of Thermodynamics
If two systems are in thermal equilibrium with a
third system,
they must be in thermal equilibrium with each
other.
Thermal Equilibrium = Same temperature
Thermal Equilibrium = No heat flow
Fowler and Planck stated it in the 1930s
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Dec 29, 2012
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Exergy (Available Energy)
Surroundings: outside the system boundaries
Environment: the area of the surroundings not affected by
the process at any point
(For example, if you have a hot turbine, the air next to the
turbine is warm. The environment is the area of the
surroundings far enough away that the temperature isn’t
affected.)
Dead State: when a system is in thermodynamic equilibrium
with the environment, no more work can be done
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Dec 29, 2012
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Exergy (Available Energy)
A coal-fired furnace is used in a power plant.
Furnace delivers 5000 kJ/s of heat energy at 1000 K.
The environment is at 300 K.
Determine the maximum percentage of the heat that can be
converted to work.
Determine the maximum work possible.
This is the maximum work output possible between the given
state and the dead state, i.e., the heat’s exergy.
In this case, 30% of the 5000 kJ/s unavailable energy—it
can’t be converted to work.
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Exergy (Available Energy)
The Second Law tells us that the available energy (or exergy)
diminishes every time energy is used in any process.
Note that energy is conserved. So energy can’t diminish.
It is the energy available for doing work (exergy) that
diminishes.
This means that the available energy (or exergy) in the
universe as a whole is constantly diminishing.
Since the available energy driving a real process is always
lowered, all real processes are irreversible.
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Dec 29, 2012
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Exergy (Available Energy)
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.
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Dec 29, 2012
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Entropy
The irreversible loss of some energy from a system to its
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.
That is, entropy of an (isolated) system always increases.
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The energy of the universe is constant (First Law).
Exergy (that is, energy available for doing useful work)
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.
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Dec 29, 2012
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Combustion Fundamentals
Combustion is commonly known as burning.
Combustion is a process in which oxidizable
materials are oxidized by use of oxygen
(present in the air).
Combustion is a exothermic reaction, which
means heat energy is released during
combustion.
CH4 + 2 O2 → CO2 (g) + 2 H2O(g) + heat energy
CxH2y + (x+y/2) O2 → x CO2 (g) + y H2O (g) + heat energy
2 H2 + O2 → 2 H2O(g) + heat
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Combustion Fundamentals
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.
CH4 + 2 O2 → CO2 (g) + 2 H2O(g) + heat energy
CxH2y + (x+y/2) O2 → x CO2 (g) + y H2O (g) + heat energy
2 H2 + O2 → 2 H2O(g) + heat
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Combustion (or Fire) Triangle
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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,
- which causes a small explosion which generates work.
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Combustion Engine
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Combustion Engine
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Combustion Engine
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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.
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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.
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Dec 29, 2012
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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 29, 2012
80
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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 29, 2012
81
http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html