Prof. R. Shanthini Dec 10, 2011 1 Module 01 Energy Basics Energy Power Forms of energy Thermodynamic laws Entropy Exergy Combustion fundamentals

Prof. R. Shanthini Dec 10, 2011

1

Module 01

Energy Basics

Energy

Power

Forms of energy

Thermodynamic laws

Entropy

Exergy

Combustion fundamentals


2

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


3

• 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.


4

• What is energy?


• What is work?

– force exerted over a distance (scientific definition)

FF is the force pushing the ball


5

• What is energy?


• What is work?

– force exerted over a distance (scientific definition)

F

D

Work = F x D

D is the distance over which the ball is moved

F is the force pushing the ball


6

• What is energy?


• What is power?

– power is the rate at which work is done

Work = Force x Distance

Power = Work / Time


7

• What is the unit of Energy?

• What is the unit of Work?

• What is the unit of Power?


8

Units for energy / work

joule in SI-system

1 J (joule) = 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


9

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

SI multiples for joules (W)

http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)


10

Units for power

watt in SI-system

1 W (watt) = 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


11

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

SI multiples for watts (J)


12

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


13



Global Consumption = 15 TW = 15x1012 W

= 250,000,000,000 of 60 W bulbs

= about 35 of 60 W bulbs per person


14


Global Consumption = 15 TW = 15x1012 J/s = 54x1015 J/h



15

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.


16

• 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)


17

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)


18

http://www.aps.org/policy/reports/popa-reports/energy/units.cfm

For more on energy units and conversions,

Visit

The American Physical Society Site


19

• Kinetic Energy: • Potential Energy:• Thermal (or Heat) Energy:• Chemical Energy:• Electrical Energy:• Electrochemical Energy: • Sound Energy: • Electromagnetic Energy (light):• Nuclear Energy:

Basic Forms of Energy


20

• 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.

Source: http://euclidstube.com/poe/Thermodynamics.ppt

Basic Forms of Energy (continued)


21

• 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.




22

• 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".




23

• 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.




24


• 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".



25


• 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.



26

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.


27

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: ……………………………………


28

Thermodynamicsis 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.


29

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.


30

Qin Wout


Heat energy that entered the system

Work energy that left the system

System

Energy of the system

E


31

Qin Wout

Efinal - Einitial = Qin – Wout

ΔE = Qin – Wout


E


32


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.


33

Hot reservoir at TH K

Wout

Qin

Heat Engine

Apply First law to Heat Engine

Cold reservoir at TC K

Qout

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.

Example: Diesel cycle auto.howstuffworks.com/diesel.htm

http://auto.howstuffworks.com/diesel.htm


34


Wout

Qin

Heat Engine

Apply First law to Heat Engine


Qout

Qin = Wout + Qout

First law gives the following relationship:


35


Wout

Qin

Heat Engine

We like to have an engine that converts all heat into work. That is, we would like to have

Is it possible?

Qin = Wout


36

Qout


Wout

Qin

Heat Engine

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.

Second Law of Thermodynamics

WHY?


37


Wout

Qin

Heat Engine



Qout

ηCarnot

= TC

1 - TH

Maximum possible thermal efficiency of the heat engine is

< 1ηCarnot

Since TC can never be zero,


38


Wout

Qin

Heat Engine



Qout

ηth = Wout

Qin

< ηth ηCarnot

< 1

Thermal efficiency of the heat engine is


39


Wout

Qin

Heat Engine



Qout

Qout ≠ 0

ηth = Wout

Qin

Thermal efficiency of the heat engine is

< 1

Qin ≠ Wout

Some heat is thrown away.


40

EntropyWhen 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.


41

ExergyThe 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.


42

ExergyThe 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.


43

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.


44

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


45

Third Law of Thermodynamics

It is impossible to reach absolute zero in a finite number of steps.


46

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.

Combustion Fundamentals


47

Combustion (or Fire) Triangle


48

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.


49

Combustion Engine


50

Combustion Engine


51

Combustion Engine

http://bancroft.berkeley.edu/Exhibits/physics/images/origins18.jpg


52

Combustion Engine

http://images.yourdictionary.com/images/main/A4gastrb.jpg


53

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.

http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html



54

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.




55

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




56

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 asCH4 + 1.25 x 2 (O2 + 3.76 N2) -> CO2 + 2 H2O + 0.5 O2 + 9.4 N2




57


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:

Excess Air%

Carbon Dioxide - CO2 - in Flue Gas (% volume)Oxygen in Flue Gas for all fuels (% volume)

Natural Gas

Propane Butane

Fuel OilBituminous Coal

Anthracite Coal

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


Documents

Prof. R. Shanthini Dec 10, 2011 1 Module 01 Energy Basics Energy Power Forms of energy Thermodynamic laws Entropy Exergy Combustion fundamentals