Transcript Thermodynamics, Heat Energy, and how we benefit from it

Demos
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Shuttle Tile and Oven
Mohair fuzz
Candle
Fire Syringe
Deck of Cards
Pasco Cylinder and Temp Sensor
Bicycle Tire and Digital Thermometer
Steam Engine and generator + bulb
Stirling Engine
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DI Water , Ethanol
Thermodynamics,
Heat Energy, and how we
benefit from it.
Outline
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What is Thermodynamics
What is Heat and temperature
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Definition
What makes Heat flow (heat transfer)
Specific Heat
How heat flows
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Conduction
Convection
Radiation
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Laws of Thermodynamics and Entropy
Doing work on a Fluid
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Fire Piston - before the invention of the Match Head
Some common thermodynamic cycles
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Otto Cycle and other heat engines
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Electromagnetic Spectrum
Combustion Process
Stirling
Refrigeration and heat pumps
Why 100% efficiency is theoretically impossible (the Heat Tax)
Common engines
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Steam Engine
Diesel Engine
Electric Engine
What is Thermodynamics?
Thermo means “heat" and Dynamics
relates to "movement"; in essence
thermodynamics studies the movement of
heat energy and how that energy makes
mechanical movement (i.e. does work).
Thermodynamics is a science about the
effects of changes in temperature,
pressure, and volume and how these
changes effect a physical system.
(e.g. a car engine, an air conditioner)
What is Heat?
Heat Energy is a type of kinetic energy
Heat Energy relates to Thermal Energy (or
internal energy)
Thermal Energy is the sum of the kinetic energy,
½ mv2 , of ALL the individual atoms in a system
or object.
Heat is the energy that flows from one
object to another due to a temperature
difference.
When Energy flows from a hot object to a
cold object, the energy is called Heat
http://hop.concord.org/htu/htu.concepts.flow.html
Before 1800, Heat was thought to be an
invisible fluid that flowed between objects
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Objects were thought to
contain fixed quantities of
heat.
Benjamin Thompson
observed that canons bored
with dull tools became very
hot while those bored with
sharp tools did not get as
hot. The heat generated had
nothing to do with the size of
the canon.
Thompson suggested that
heat came from friction (or
mechanical energy).
http://honolulu.hawaii.edu
James Joule tests the predictions:
James Joule’s
experiment
proved that heat
was a form of
energy. In this
experiment the
kinetic energy of
the paddle is
transferred to
thermal energy in
the water, as
measured with a
sensitive
thermometer.
http://www.geocities.com/bioelectrochemistry/joule.htm
Two objects in contact on a microscopic level:
Slow moving
http://hop.concord.org/htu/htu.concepts.flow.html
Fast moving atoms with a lot of random
motion collide with slower moving atoms.
As kinetic energy is transferred from the
fast moving atoms to the slower moving
atoms, we say that the warmer side gave
up heat to the colder side and that heat was
transferred.
Fast moving
What is Temperature?
Temperature is a measurement of the average thermal
energy of the particles in a substance.
Heat flows due to temperature differences.
No heat is transferred between two objects that are at
the same temperature (i.e. in thermal equilibrium).
A cup of boiling water is at the same temperature as a
gallon of boiling water, but the gallon of boiling water
has more thermal energy than the cup.
Which object has higher thermal energy?
http://picasaweb.google.com/peppermint.patti1960
Heat Capacity
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Heat Capacity of an object is the required
energy needed to raise the object’s
temperature by one degree.
A large quantity of matter has a larger
heat capacity than something smaller
Our oceans and atmosphere have large
heat capacities due to their large sizes.
Specific Heat
The measure of the heat energy required
to increase the temperature of a unit
quantity of a substance by one degree.
Copper
0.385 Joule/gr oC
Dry Air
Humid Air
Water
Concrete
Sand
1.0035 Joule/gr oC
1.0102 Joule/gr oC
4.1813 Joule/gr oC
0.88 Joule/gr oC
0.42 Joule/gr oC
Second highest
specific heat, next
to Ammonia
Specific Heat of Water
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Very high
Earth’s ocean store vast amounts of thermal
energy – these large heat reservoirs regulate the
earth’s temperature.
Unfrozen lakes moderate surrounding climate
Water filled walls make good thermal mass
Water filled walls as thermal mass
http://www.energybulletin.net
Using plant material as solar mass
McGill University, Montreal – Solar Decathlon 2007
http://www.solardecathlon.org/
How does Heat flow?
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Conduction – the transfer
of heat energy by making
direct contact with the
atoms/molecules of the
hotter object
Convection – the transfer
of heat due to a bulk
movement of matter from
hotter to colder areas
Radiation – energy
transferred by
electromagnetic waves
http://www.williams.edu
Conduction
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When two objects are in direct contact,
particles in the hotter object are moving
faster and will collide with slower moving
objects in the colder object.
When this happens, heat flows.
Energy is transferred from the hot object
to the cold object.
Touch the wood table and then
touch the metal legs of the table…
Both Objects are at the same temperature, but
the metal feels colder, why?
You are at a higher temperature than any nonliving object in the room, therefore heat is
transferred from your body to both the wood
and the metal.
The metal conducts heat better than the wood
because there are a lot of free electrons in
metals, therefore mobile electrons take heat
from your hand faster than wood.
The rate of heat transfer depends on:
1. The Temperature difference
2. And the Thermal Conductivity of the
Materials
Shuttle Tile white-hot at 2300 oF
The tile is 10% pure silica
fibers and 90% air. The
high percentage of air
makes the tiles very
lightweight.
Tile has very low thermal
conductivity due to trapped
air and the low conductivity
of long glass fibers.
http://www.answers.com/topic/space-shuttle-thermal-protection-system
Is air a good thermal insulator?
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Thermal Insulation is the method of preventing
heat from entering or escaping from a container.
Stagnant air is a good thermal insulator
Coats, feathers, fur, hair, fiberglass insulation, &
straw bales all trap tiny pockets of air.
The ocean of air over your head helps keep the
earth cool during the day and warm during the
night.
Air has high specific heat.
Heat energy is transmitted
by collisions from
neighboring
atoms/molecules.
http://www.ucar.edu/
More examples of Conduction
www.backpackgeartest.org
www.broadys.co.nz
Convection
Buoyancy forces
cause bulk movement
of the water.
www.physics.arizona.ed
More examples of Convection
www.physics.arizona.edu
www.weatherquestions.com
Rising hot air and falling cool air sets
up convection cells.
Heat from the earth’s core comes from
ancient energy left from earth’s formation
and radioactive elements which decay and
release heat.
http://www.incois.gov.in
Heat from the earth’s core causes slow moving convection
cells in the earth’s mantle. The earth’s crust spreads at
mid-ocean ridges by 2-3 cm per year.
Northern Atlantic cold
water sinks. This pulls
in warmer water from
the Gulf Stream. This
heat transfer
phenomenon
determines how warm
or cool European
climates will be.
Fresh water is less
dense than salt water.
As Greenland’s ice
fields recede more
fresh water enters the
North Atlantic possibly
impacting normal
oceanic convection
patterns.
Oceanic Convection
Forced Convection
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Forced Convection is not due to the
natural forces of buoyancy induced by
heating.
Instead, there is a external force that
causes the fluid to convect, such as a fan
or a pump.
Convection Ovens
A fan circulates the air so hot
air is not trapped at the top of
the oven. More cookies can
be baked at one time and all
will cook at the same rate.
Ceiling Fans
www.sleekhome.com
In both hot and cold weather,
ceiling fans are useful for
circulating air to force
convection.
Rooms with high ceilings are a
problem during the winter as
the hot air rises and moves
away from the floor area.
Heat Transfer from Radiation
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All matter that has thermal energy will emit
infrared electromagnetic radiation.
We can feel this when we put our hands close to
a fire.
This type of heat transfer requires no medium.
Electromagnetic radiation travels at the speed of
light through a vacuum.
http://www.charlesandhudson.com
http://www.newt.com
Infrared Radiation
All objects with thermal
energy emit Infrared
Radiation (even ice)
Infrared radiation is
invisible to our eyes but
we can feel it as heat
Nasa.gov
The Sun’s energy is transferred to
earth by electromagnetic waves
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Visible Light
Infrared radiation
Ultraviolet (UV)
http://www.foxnews.com
Electromagnetic Spectrum of Waves
http://www.hermes-program.gr
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Ionizing radiation causes matter to ionize (can
rip an electron off an atom)
Ionizing radiation carries more energy than
those waves with larger wavelengths.
The sun’s UV waves are those responsible for
burning and skin cancer.
Infrared is non-ionizing radiation.
Non-ionizing radiation is everywhere and is
considered to not be harmful.
Laws of Thermodynamics
Zeroth Law:
If two objects are in thermal equilibrium
with a third object, then they are also in
thermal equilibrium with each other.
Thermal equilibrium means an objects temperature, pressure, and
volume are not changing.
http://www.cafemakers.com
A cooling cup of coffee is NOT in
thermal equilibrium with the room.
If two cups of coffee are at
thermal equilibrium with
the room, then the two
cups are in thermal
equilibrium with each
other.
The two cups of coffee
have the same
temperature.
/www.wentapottery.com
If the two cups are put in
contact with each other no
heat will flow.
First Law of Thermodynamics:
(The good news!)
Energy is Conserved. Energy can not be destroyed.
In an isolated system, the total energy stays the same.
Energy can be converted from one form to another.
Thermal Energy can be converted into another form
of energy!
What is Entropy?
Entropy = total disorder of an object/system
Disorder is the sum of the thermal energy
plus the physical disorder.
Entropy always increases with time!
Examples of increasing entropy
Wikipedia.com
www.wiley.com
Playing “52 pick up”
Direction
Is possible
+
Heat, light, ash,
particulates, gases
Direction
Is impossible
+
Heat, light, ash,
particulates, gases
Energy flows in one direction – towards a
more disordered state
The Second Law of Thermodynamics:
(The bad news!)
An isolated system gets more disordered with
time.
Entropy always increases with time.
What does this mean to us?
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It is impossible to construct an engine that
converts all its thermal energy into useful work.
The exhaust must be hotter than the incoming
air.
100% efficiency is impossible –there must be
some unusable energy because entropy must
increase.
We’re going to get old and die
The house is going to need cleaning again!
Why is 100% efficiency
theoretically impossible?
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If machine operates in
a cycle, some energy
must be used to reset
the machine.
Parts of machine will
absorb some of the
heat.
Exhaust must be
hotter than incoming
air, due to 2nd law.
This hot exhaust
represents wasted
energy.
http://commons.wikimedia.org
Doing work on a Fluid
When a fluid is compressed, work is done
on the fluid.
This work/energy is converted into
thermal energy within the fluid.
Each molecule has more kinetic energy so
the temperature of the fluid increases.
As air is rapidly
compressed, it can reach
400-500 degrees, allowing
tinder to ignite.
Fire Piston
www.grannysstore.com
The compressed air is the
heat source as well as the
oxygen needed to ignite
the tinder.
Fire piston are thought to
be prehistoric fire starting
devices, used in South East
Asia and South Pacific.
For more info see:
http://en.wikipedia.org/wiki/Fire_piston
The modern match
evolved during the
1800’s. Prior to 1900,
fires had to be
maintained or started by
creating heat through
friction.
Wikipedia.com
The Bow and
Drill used by
Native Americans
Many people used
flintlock guns.
http://wildwoodsurvival.com
But fluids can do work
on surroundings
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A compressed gas will experience an increase in
pressure (as well as an increase in temperature
if compression is fast).
When a pressurized gas expands it’s thermal
energy decreases because it is doing work (it is
exerting forces as it expands).
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Ex. Air escaping from a bicycle tire feels cold.
Heat Engines
A cycling machine/engine that converts
thermal energy into mechanical energy
(also known as work)
Examples:
4-stroke engine (OTTO Cycle)
Steam Engines
Stirling Engine
Combustion can be
used to energize a fluid
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Fuel source
Oxygen
Heat
http://www.fs.fed.us
Steam Engine invented in 1712
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Using combustion and
water to create
steam.
External Combustion
Used to pump water,
power ferries, trains,
& factories.
Demand for coal rises
Ushers in the
Industrial Revolution
HowStuffWorks
A boiler is used to heat
water to create steam.
This high pressure fluid
in turn does work on
the pistons.
Working fluid (steam)
is heated through a
heat exchanger. Fuel
is external to working
fluid.
About 6% efficient
HowStuffWorks
http://science.howstuffworks.com/steam1.htm
Click for animation
Coal and Steam Powered Factory
Briggs and Stratton Website
Stirling Engine - 1816
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Closed Cycle – working fluid is
contained within the system
Highest efficiency possible
Higher capital costs
Heat Source and Heat Sink needed
The Power Piston lags the Displacer by 90o
http://en.wikipedia.org/wiki/Stirling_engine
Gasoline Engine - 1876
Gasoline Engines
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Internal Combustion – burning takes
place inside the engine
Based on a four-stroke combustion
cycle called the
Otto Cycle:
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Intake
Compression
Combustion
Exhaust
http://auto.howstuffworks.com/engine1.htm
Click for animation
Diesel Engine - 1876
Diesel engines do not have spark
plugs because similar to the fire
piston, the compression of the gas
and air mixture is great enough to
automatically ignite the fuel.
Gas is injected into cylinder after air
is compressed. This allows for
greater compression, and higher
efficiency.
http://auto.howstuffworks.com/diesel1.htm
Click for animation
BioDiesel
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Made from plant or animal oils
Chemically treated so that
BioDiesel won’t solidify at low
temperatures or clog fuel lines
Very simply chemistry
Make Magazine Vol#3
Efficiency of Engines
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IC Engine is only 20-30% efficient
Diesel is more efficient due to the greater
compression rate and ability to extract more work
out of the fuel
Why 100% efficiency is impossible?
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At least some of the energy must be passed on
to heat a low-temperature energy sink
This is due to the 2nd Law of Thermodynamics –
Entropy must increase!
Engine needs to be reset.
Engine parts will absorb some of the heat
energy.
Early cars employed three technologies
1.
2.
3.
Steam powered
Electric battery powered
Gasoline and Diesel powered
Stanley Steam Car 1912
Steam Cars
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Heavy
Slow to heat up and
start
Required carrying
both fuel and water
http://www.steamcar.net/my-85.html
First electric vehicles (EV)
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Edison worked on battery
storage believing that
electricity would power
future cars
In 1900, roughly a third of
all vehicles sold are EVs
EVs were marketed to
women and for urban
areas
Morrison’s 4-horse power EV
with a range of 50 miles.
Circa 1888
Thomas Edison circa 1900
Early electric vehicles
Detroit Electric Carriage - 1912
Waverley Automobile Co.
Early Gas powered cars
Karl Benz was the first to
commercialize a gas powered
motorwagon in 1885
Why did EVs and Steamers fade away?
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Gasoline and Diesel have high energy
densities
Oil found in Texas
Greatest need for cars and trucks was in
rural areas, therefore long range was
needed.
Steamers too heavy on unpaved roads
Gas powered cars started quickly
Henry Ford perfected the assembly-line,
making his cars the most affordable
Why was gasoline the chosen
fuel source for the automobile?
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Gasoline has 1000X the energy as an equal
weight of batteries.
Gasoline has 4.5X more energy per gallon than
liquid hydrogen.
Gasoline has 2X the energy of coal for the same
weight
Gas has slightly less energy per volume as
veggie oil
Gasoline combines with Oxygen when it burns.
The Oxygen is free and does not have to be
carried.
Huntington Beach 1928
Beaumont, Texas on Spindletop Hill
The Evaporator
Refrigeration:
A vapor compression cycle
Heat leaves the
fluid, heating the
kitchen floor and
condensing the
fluid.
Heat flows
into fluid
http://physics.bu.edu
The compressor on the
bottom compresses the
working fluid raising its
temperature.
In the condenser coils,
heat leaves the fluid and
enters the room. This
condenses the fluid into
a liquid.
When allowed to expand,
the temperature of the
liquid drops dramatically.
This cold fluid absorbs
heat from the inside of
the refrigerator, causing
the fluid to evaporate
and turn back into a gas.
http://www.lpappliances.com
Which law of Thermodynamics
does the following video
demonstrate?
http://www.youtube.com/watch?v=U82e
WptFxSs
Internal Combustion vs. External Combustion
External Combustion – the fluid doing the work
(working fluid) is heated externally.
Internal Combustion – the fluid doing the work is
heated by burning a fuel internally inside a cylinder
pushing down on a piston
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Pros of IC
 electric starter, so
easier and quick to
start up
Cons of IC
 By-products of
combustion in exhaust
gases
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Major
Plus
Pros of EC
 Fuel can be anything
Cons of EC
 Slow to start
 Heat exchanger needed
 If steam is the working
fluid:
 Boiler needed
 Water freezes at low
temperatures