Presentation outline:

• Some semantics -- the meaning of the word „alternative”• List of those we can call “alternatives”• If we are interested in “alternatives”, why should we also know much about energy sources that are not “alternatives”? I. e., about fossil fuels, and how they are used?• Major fossil fuel resources, how long will they last, and their distribution over the globe.• What are fossil fuels used for? Major ways of using them.• Heat engines – the main tools of coverting fossil fuel energy to other usable forms.• Types of heat engines.•Some thermodynamics: First Law, and then a longer introduction to the Second Law.

The title of this course is Energy Alternatives

Let’s first precisely define what it means. Take the WebsterDefinition and look up Alternative. We find:Adjective:1: offering or expressing a choice <several alternative plans>2: different from the usual or conventional: as ● a: existing or functioning outside the established cultural, social, or economic system <an alternative newspaper> <alternative lifestyles> b: of, relating to, or being rock music that is regarded as an alternative to conventional rock and is typically influenced by punk rock, hard rock, hip-hop, or folk music c: of or relating to alternative medicine <alternative therapies> Noun:1 a: a proposition or situation offering a choice between two or more things only one of which may be chosen b: an opportunity for deciding between two or more courses or propositions2 a: one of two or more things, courses, or propositions to be chosen ● b: something which can be chosen instead <the only alternative to intervention>3: alternative rock music

Clearly, the highlighted are the most appropriate Energy Alternatives.

In short: generally, the term Energy Alternatives refers to resourcesthat can be chosen instead of the established methods of energyproduction.

Traditional fuels & resources;

• Coal (since early 1700s);• Oil (since mid-XIX Century);• Natural gas (as above);• Hydropower (many millennia!);• Nuclear fission (since 1950s).

Extracting energyfrom the first threeinvolves burning

Energy alternatives:

• Solar energy (direct usage);• Wind (solar, too! – indirectly);• Bio-fuels (again, solar!);• Hydropower (one more solar!);• Nuclear (returning to favors);• Ocean waves;• Tides;• Geothermal energy;• ……. (probably a few items can be still added).

“Traditional” methods – we don’t like them (why?).Think green:

They are our enemy! We want to eliminate it!

Well – and keep in mind what the greatest militaryleaders in history always used to say:

Rule Number Onefor a victoriouscampaign:

Know your enemy!Learn about allits weaknessesand strengths!

Fossil fuels – basic facts and numbers:

Major – global resources:

• Coal: 997,748 million short tons (4,416 BBOE; 2005)

• Oil: 1,119 to 1,317 billion barrels (2005-2007)

• Natural gas: 6,183 - 6,381 trillion cubic feet (1,161 BBOE; 2005-2007)

Minor (or not yet fully exploited):• Tar sands (contain “bitumen”, a form of heavy oil): 1.7 trillion(!) BBOE; • Oil shales (as above) 411 gigatons, or 2.8 to 3.3 trillion(!) BBOE;

• Methane hydride – (resources unknown, by some believed very large).

BBOE = Billion Barrels of Oil Equivalent

Energy conversion – a convenient program

Flows (daily production) during 2006

Oil: 84 million barrels per day;Gas: 19 million barrels oil equivalent per day {MBOED} Coal: 29 million barrels oil equivalent per day MBOED

How long will those resources last?

Years of production left, due the most optimistic reserve estimates (Oil & Gas Journal, World Oil)

Oil: 43 years

Natural Gas: 167 years

Coal: 417 years

The distribution of coal, oil and gas deposits by country, shown using colorsRed – largest resources; Black – smallest resources

COAL: OIL:

GAS: TOTAL:

(FYI, not for any longer discussion in class)

How are fossil fuels used? We just burn them,that’s all! But in many different ways:

• Simple combustion;

• To generate heat needed in many types of industrial processes, e.g., smelting, chemical synthesis, ….

• In heat engines, using various types of combustion, propelling cars, trucks, railway engines, planes, ships, …

• In heat engines, to generate mecha- nical energy, and then electric power;

Steam engine and internal combustion engine animations

Another Web site with engine animations

Major heat engine types:

• Steam engines (in historical context, mostly).• Internal combustion engines• Steam turbines and gas turbines.

Steam Turbine Animation

Conclusions: Heat (or, rather thermal energy)can be transformed into mechanical energy. And there is a range of heat engines that can be harnessed to perform many useful tasks.

Unfortunately… The reality is notso brilliant as one might think.

There is one annoying “troublemaker”that adds much gloom to the picture.

The name of that troublemaker isThe Second Law of Thermodynamics

So – even more unpleasant news: we have to go back to physics!

If we want to know what the 2nd Law is about, we have toknow first what the 1st Law of Thermodynamics says, right?

About the First Law of Thermodynamics:

A system: a single body, ormore bodies that in contact with one another.

There is a physical quantity called theINTERNAL THERMAL ENERGY of asystem – or “internal energy” in short.Conventionally, it is denoted as U .

SYSTEM:

U:Energy may be added to the system, thus increasing its U

(we call such a process “heating”).-- or –

Energy may be taken away from the system, thus lowering its U(we call such a process “cooling”).

There is a temperature, at which no more energy can be removed from the system.We call it the absolute zero. Its value is:T = - 492.3 ˚F, or in the SI system, T = 0 K.

1 K = 1.8 ºFWater freezesat 273.15 KBoils at 373.15 K

Celsius Scale:Water freezes at 0 ºC, boils at100 ºC.

So, the incrementin the SI scale andin Celsius scale isthe same: 1ºC= 1 K.

Now, QQQ (Quick Quiz Question):

Energy is added to a system. Its temperature: (a) Increases(b) Decreases(c) Does not decrease(d) Does not increse

Now, the First Law: essentially, it’s the Energy Conservation Law, but expressed in a way specifically applying to thermal phenomena:

WQU The total change inthe system

internal energy

The change dueto transfer of

heat (heat flowingin or out from

another system)

The change due tomechanical work

done ON the system,or the work delivered

BY the system (then - )

IMPORTANT! A common misconception is to confuse HEAT with the INTERNAL ENERGY. Internal energy is the amount of energycontained by the system. Heat is the energy that flows in or outfrom/to a warmer/cooler body which is in contact with the system.

The First Law was an easy part. But in order to explain whatthe Second Law talks about, we have to introduce the notionof ENTROPY.

Entropy is widely regarded as one of the most difficult conceptsin university physics curriculum. It’s a parameter that characte-rizes the thermal state of a system. Other state parameters arethe internal energy U, volume V, the amount of substance (usu-ally expressed as the number of moles N – a mole consists of 6.0221023 molecules of a given substance – who can tell whysuch an “exotic” number?), the temperature T, and pressure p.They are all “intuitively clear”, am I right?

In contrast, entropy, conventionally denoted as S, is an abstractfunction. Its mathematical definition is not particularly difficult:

However, for a student it may not be a straightforward thing to understand its physical meaning, and “what it is good for”.

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This slideis notforgoingthroughit indetail inclass,but rather for youto readbeforeor afterthe class.This also ap-lies to the next slide.

Entropy is an even greater challenge for an instructor, than for a student – I mean, doing a “quality work” when teaching thistopic. Dr. Tom has been teaching thermal physics at OSU formore then ten years, and he knows that trying to tell everythingrelevant about entropy in the course of a single class hour wouldnot be a “quality job”. Rather, in the thermal physics classes he teaches he spends several hours, introducing the entropy in a systematic manner, step by step. Entropy is not a good topic for being taught in a “crash-course” fashion.

This course is not a thermal physics course, and entropy is “just a small episode”. We can only talk about that briefly.Therefore, this presentation is limited to some basic facts thatI am asking you to accept without proof.

Here we define the entropy as it is done in classical ther-modynamics, which is a macroscopic theory. In statistical ther-modynamics, which is a microscopic approach, one uses a dif-ferent definition – in terms of thermal disorder:where Ω is “the measure of disorder”. Both definitions are equi-valent, as can be shown – however, the latter is not particularly useful for analyzing the performance of thermal engines, andtherefore we will use the “classical definition”

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Entropy – important facts “in a nutshell”:The entropy of a thermally isolated system (meaning: no heat can be transferred in or out) may only increase or remain constant in time, but it cannot decrease. In other words:

This is the Second Law of Thermodynamics – or, rather one of its many formulations. There

are many other formulations that one can find in the literature,but they are all equivalent.One funny fact: the shortest of all those formulations states: It is not possible to build a Perpetual Motion Machine of the Second Kind

.0systemisolated

dt

dS

What is the “Perpetual Motion Machine of the Second Kind”? When the EnergyConservation Law was formulated, it became clear that building a purely mechanicalperpetual motion device was not possible. But some “inventors” did not give up!They said: Well, we accept that work cannot be created out of nothing. But note thatthat oceans are almost infinite reservoirs of thermal energy. Let’s convert this energyto work – such a machine would not violate the Energy Conservation Law!

Q: Who derived the Second Law, and how?A: It has not been “derived” mathematically. It is an EMPIRICAL LAW,based on zillions of experimental results and observations. What scientist only did, they “digested” all that information and formulatedThe conclusion in the form of a law of physics.

Entropy in a nutshell, cont. – situations in which the entropy in a thermally isolated system increases:

The entropy must increase when an irreversible process occursin the system. Example:

T1 T2 T1 T2

Tf Tf

T1 > T2

1. Two bodies of different temperatures in an isolated system.

2. Bodies brought into thermal contact. Heat flows.

T2 < Tf < T1

3. After a while, equilibrium is reached. Now the two bodies have the same temperature.

We will work this example inclass on the blackboard, andwe will show that the entropyindeed increases in such a process.

The calculations below will be done in class on the board – this slide is only for you to read before the class, or later when preparing for a test.

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The calculations below will be done in class on the board – this slide is only for you to read before the class, or later when preparing for a test.

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The calculations below will be done in class on the board – this slide is only for you to read before the class, or later when preparing for a test.

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Example of a reversible processThere is a cylinder, made of a thermally insulatingmaterial, with a heavy piston, also insulating. Initi-ally, the gas is compressed and exerts an upward force on the piston larger than it weight. Whenreleased, the piston starts mowing up. The gas pressure gradually drops. The piston oscillatesup and down, in analogy to a mass on a spring.The process is reversible: first, the gas energy Uis converted into potential energy of the piston,and then the sequence is reversed, going throughthe same stages as when moving up. The gas first delivers, thenabsorbs work, but its entropy remains constant during the process.

In contrast,in reversible

processesthe system

entropy doesnot change

Another example of an irreversible process: twodifferent gases in a container:

The container is dividedinto two chambers of equal volumes V by a

partition, and each gas occupies a separate

chamber

The partition opens, the gases spontaneouslymix, and now the gas mixture occupies a

volume of 2V.

Plugging the hole willnot return the system to the initial state. Theprocess is irreversible!

Ideal gas processes

One more thing we need: the Ideal Gas Laws

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There are several processes that were given special names. We will soon need to use two of them:

• Isothermal expansion/compression: the gas temperature is kept constant throughout the process, thus pV = const.

• Adiabatic expansion/compression: no heat flows in or out during process, meaning that Q = 0, and consequently, since S = Q / T , there is no change in the entropy. Therefore, the process is often called “isoentropic” expansion/compression.

Carnot Engine animation

Another one

CarnotCycle:

(or CarnotEngine, ifyou prefer

“Engine”):

P-V diagram: Start lookingHERE and travelclockwise

STQTT

dQdS

NRTUNRTpV

:constant at that so , :Entropy

;2

3 :energy Internal ; : gas Ideal

Carnot Engine operation First stroke, A→B : Isothermal expansion at high T :

At point A

At point B

T = Th = const., so that U = const. All heat absorbed converted to work!!

BABABA STQW h

“Hot source”:

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2

3 ; :gas Ideal

Carnot Engine operation (2) Second stroke, B→C : Adiabatic expansion, no heat input, S = 0 :

At point B

At point C

Now the gas still delivers work, but uses its internal energy for that:

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2

3 ; :gas Ideal

Carnot Engine operation (3) Third stroke, C→D : Isothermal compression at low temperature (Tc):

T = Tc = const., so that U = const. All work absorbed is dumped in the form of heat to the “heat sink”!!

DCDCDC STQW c

“Heat sink”: At point C

At point D

It’s a negativevalue, keep inmind!

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2

3 ; :gas Ideal

Carnot Engine operation (4) Fourth stroke, D→A : Adiabatic compression, no heat input, S = 0 :

The gas still absorbs work, but energy cannot get out in the form of heat, so all work goes to increasing the internal energy, thus heating up the gas:

)(2

3hc TTNRUUW ADAD

Back at point A

At point D

A negativevalue, note.

Let’s collect all results from the above analysis in a table:

Now, calculating the Carnot Engine efficiency will be a piece of cake!Column 2 yields:

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(continued:)

This is which we call the “thermodynamic efficiency” – even thougha better term would be “inefficiency” :o)))