Demos

1
Demos

• 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
• DI Water , Ethanol

2
Thermodynamics, Heat Energy, and how we benefit
from it.
3
Outline

• What is Thermodynamics
• What is Heat and temperature
• Definition
• What makes Heat flow (heat transfer)
• Specific Heat
• How heat flows
• Conduction
• Convection
• Radiation
• Electromagnetic Spectrum
• Laws of Thermodynamics and Entropy
• Doing work on a Fluid
• Fire Piston - before the invention of the Match
  Head
• Some common thermodynamic cycles
• Otto Cycle and other heat engines
• Combustion Process
• Stirling
• Refrigeration and heat pumps
• Why 100 efficiency is theoretically impossible
  (the Heat Tax)

4
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).

5

• 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)

6
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.

7

• 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
8
Before 1800, Heat was thought to be an invisible
fluid that flowed between objects

• 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
9
James Joule tests the predictions
James Joules 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
10
Two objects in contact on a microscopic level
Fast moving
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.
11
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.

12
Which object has higher thermal energy?
http//picasaweb.google.com/peppermint.patti1960
13
Heat Capacity

• Heat Capacity of an object is the required energy
  needed to raise the objects 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.

14
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 1.0035
Joule/gr oC Humid Air 1.0102 Joule/gr
oC Water 4.1813 Joule/gr oC Concrete 0.88
Joule/gr oC Sand 0.42 Joule/gr oC
Second highest specific heat, next to Ammonia
15
Specific Heat of Water

• Very high
• Earths ocean store vast amounts of thermal
  energy these large heat reservoirs regulate the
  earths temperature.
• Unfrozen lakes moderate surrounding climate
• Water filled walls make good thermal mass

16
Water filled walls as thermal mass
http//www.energybulletin.net
17
Using plant material as solar mass
McGill University, Montreal Solar Decathlon 2007
http//www.solardecathlon.org/
18
How does Heat flow?

• 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
19
Conduction

• 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.

20
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
  non-living 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.

21

• The rate of heat transfer depends on
• The Temperature difference
• 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
22
Is air a good thermal insulator?

• 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.

23
Heat energy is transmitted by collisions from
neighboring atoms/molecules.
http//www.ucar.edu/
24
More examples of Conduction
www.backpackgeartest.org
www.broadys.co.nz
25
Convection
Buoyancy forces cause bulk movement of the water.
www.physics.arizona.ed
26
More examples of Convection
www.physics.arizona.edu
www.weatherquestions.com
Rising hot air and falling cool air sets up
convection cells.
27
Heat from the earths core comes from ancient
energy left from earths formation and
radioactive elements which decay and release heat.
http//www.incois.gov.in
Heat from the earths core causes slow moving
convection cells in the earths mantle. The
earths crust spreads at mid-ocean ridges by 2-3
cm per year.
28
Oceanic Convection
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 Greenlands ice fields
recede more fresh water enters the North Atlantic
possibly impacting normal oceanic convection
patterns.
29
Forced Convection

• 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.

30
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.
31
Ceiling Fans
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.
32
Heat Transfer from Radiation

• 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.newt.com
http//www.charlesandhudson.com
33
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
34
(No Transcript)
35
The Suns energy is transferred to earth by
electromagnetic waves

• Visible Light
• Infrared radiation
• Ultraviolet (UV)

http//www.foxnews.com
36
Electromagnetic Spectrum of Waves
http//www.hermes-program.gr
37

• 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 suns 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.

38
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.
39
http//www.cafemakers.com
A cooling cup of coffee is NOT in thermal
equilibrium with the room.
40
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. If the two
cups are put in contact with each other no heat
will flow.
41

• 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!

42
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!

43
Examples of increasing entropy
Playing 52 pick up
44
Direction Is possible
Direction Is impossible
45

• Energy flows in one direction towards a more
  disordered state

46

• The Second Law of Thermodynamics
• (The bad news!)
• An isolated system gets more disordered with
  time.
• Entropy always increases with time.

47
What does this mean to us?

• 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.
• Were going to get old and die
• The house is going to need cleaning again!

48
Why is 100 efficiency theoretically impossible?

• 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
49
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.

50
Fire Piston
As air is rapidly compressed, it can reach
400-500 degrees, allowing tinder to ignite. 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/Fi
re_piston
51
The modern match evolved during the 1800s.
Prior to 1900, fires had to be maintained or
started by creating heat through friction. Many
people used flintlock guns.
The Bow and Drill used by Native Americans
Wikipedia.com
http//wildwoodsurvival.com
52
But fluids can do work on surroundings

• 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 its thermal
  energy decreases because it is doing work (it is
  exerting forces as it expands).
• Ex. Air escaping from a bicycle tire feels cold.

53
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
54
Combustion can be used to energize a fluid

• Fuel source
• Oxygen
• Heat

http//www.fs.fed.us
55
Steam Engine invented in 1712

• 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
56
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
57
Coal and Steam Powered Factory
Briggs and Stratton Website
58
Stirling Engine - 1816

• Closed Cycle working fluid is contained within
  the system
• Highest efficiency possible
• Higher capital costs
• Heat Source and Heat Sink needed

59
The Power Piston lags the Displacer by 90o
http//en.wikipedia.org/wiki/Stirling_engine
60
Gasoline Engine - 1876
61
Gasoline Engines

• Internal Combustion burning takes place inside
  the engine
• Based on a four-stroke combustion cycle called
  the
• Otto Cycle
• Intake
• Compression
• Combustion
• Exhaust

http//auto.howstuffworks.com/engine1.htm Click
for animation
62
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
63
BioDiesel
Make Magazine Vol3

• Made from plant or animal oils
• Chemically treated so that BioDiesel wont
  solidify at low temperatures or clog fuel lines
• Very simply chemistry

64
Efficiency of Engines

• 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

65
Why 100 efficiency is impossible?

• 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.

66
Early cars employed three technologies

• Steam powered
• Electric battery powered
• Gasoline and Diesel powered

Stanley Steam Car 1912
67
Steam Cars

• Heavy
• Slow to heat up and start
• Required carrying both fuel and water

http//www.steamcar.net/my-85.html
68
First electric vehicles (EV)

• 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

Thomas Edison circa 1900
Morrisons 4-horse power EV with a range of 50
miles. Circa 1888
69
Early electric vehicles
Waverley Automobile Co.
Detroit Electric Carriage - 1912
70
Early Gas powered cars
Karl Benz was the first to commercialize a gas
powered motorwagon in 1885
71
Why did EVs and Steamers fade away?

• 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

72
Why was gasoline the chosen fuel source for the
automobile?

• 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.

73
Huntington Beach 1928
Beaumont, Texas on Spindletop Hill
74
RefrigerationA vapor compression cycle
Heat flows into fluid
The Evaporator
Heat leaves the fluid, heating the kitchen floor
and condensing the fluid.
75
http//physics.bu.edu
76
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
77
Which law of Thermodynamics does the following
video demonstrate?

• http//www.youtube.com/watch?vU82eWptFxSs

78
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
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

• Pros of IC
• electric starter, so easier and quick to start up
• Cons of IC
• By-products of combustion in exhaust gases