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What is Thermodynamics?
Mechanical work– physical movement, e.g. lifting or pushing against friction. Electrical work – flow of current
http://www.hybridmile.com/files/2008/10/engine--1.JPG http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htm
The study of energy in the forms of heat and work and the exchange between the two.
Heat Work
• Applies to all forms of matter: solid, liquid and gas
• Relevant to very large systems (e.g. Universe) and small systems (nano-scale)
• Classical physics – does not consider individual atoms or quantum effects
Sources of Energy (Heat and Work)•Nuclear reactions are a source of heat (which can then be converted to work).
•Solar energy comes in the form of thermal radiation given off by the Sun. (Thermal radiation is a way to transfer heat from a hotter object to a colder object.) The origin of the heat of the Sun is a nuclear reaction.
•Chemical reactions are another source of heat (and hence work).
•Gravitational forces can likewise be a source of mechanical energy (work), which can be converted to electrical energy.
•Tidal energy originates from gravitational forces from the moon; can do work.
http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htmhttp://www.dailymail.co.uk/news/article-1043161/Anti-terror-patrols-secretly-stepped-power-stations.html
Combustion of wood, oil, gas and coal
From P.A. Tipler, Physics, Ch. 18
Forms of Solar Energy
Form Explanation and UseSolar radiation Direct heating of objects (e.g. buildings) by absorption of radiation (in passive syst.)
Generation of electricity by photovoltaic cells or thermal-energy conversion in the oceans (in active systems)
Photosynthesis Solar energy is converted to chemical energy in plants and fossil fuels. Solids, liquids and gases are used in combustion.
Wind power Heating of land, air and seas by solar radiation produces winds. Wind is used as a source of mechanical energy (e.g. windmills or sailing ships) or electrical energy (in generators)
Water power Sun drives water cycle (evaporation, rain) which is converted to mechanical or electrical energy (usually using gravity).
http://www.starlight-news.co.uk/StarlightSolarSystemTheSun.html
Does enough heat come from the Sun to meet human needs?
http://www.stovesonline.co.uk/wood-is-best.html
1 tonne of crude oil (7 barrels) yields 4.2 x1010 J of heat.
But humans consume about 1.3x1013 W of energy – equivalent to 300 tonnes of crude oil per sec!
What is a Joule (J)? What is a watt (W)?What is a Joule (J)? What is a watt (W)?
Energy Radiated by the Sun
Stefan-Boltzmann equation tells us the power (energy per unit of time: W = J/s) radiated per unit area (m2) of its surface:
4TPR
Sun
Earth
RSE = 1.5 x 1011 m
TSun = 5800 K
RSun = 7 x 108 m
Luminosity: L =PRA= 3.8 x 1026 WEnergy is emitted in all directions
Power radiated per unit area at RSE:
232
26
104.14
108.3 WmxR
Wx
Area
LS
SE
RE=6378 km
Power reaching the Earth:
2623 )10378.6()104.1(* mxWmxAreaS
About 70% of radiation reaches Earth:
4.9 x 1017 W: Plenty to meet human needs!
RSun
http://www.shivaranjan.com/2006/08/22/irish-company-claims-creation-of-perpetual-motion-machine/
http://theseep.wordpress.com/2008/02/10/could-perepiteia-perpetual-motion-machine-be-the-real-deal/
http://www.todayinsci.com/Books/MechApp/chap23/page28.htm
Why Study Thermodynamics: Are perpetual motion machines possible?
Three Laws of Thermodynamics (plus Zeroth Law)
Thermal expansion of girders was restricted by frictional forces. They could not expand lengthwise, so they buckled!
Joints in bridges are used to enable thermal expansion.
Why Study Thermodynamics? Thermal Expansion
(Pressure, volume and temperature are interrelated in solids.)
Why Study Thermodynamics? Understanding Gases
http://www.jamie.aarontastic.com/Low%20Pressure%20Example.JPG
Meteorology: high and low pressure
Measuring Lung Capacity
http://www.heart-watch-blog.com/images/blogs/7-2007/lung-capacity-7810.jpg
Ideal Gas:
Pressure, Volume and Temperature relationships
http://communication.howstuffworks.com/laptop.htm/printable
Why Study Thermodynamics? Heat Dissipation
Heat sinks, heat spreaders, and fans remove heat from the CPU of a laptop computer.
(The objective is to do electrical work, but heat is also given off in the process.)
http://en.wikipedia.org/wiki/File:Crab_Nebula.jpg
http://cass.ucsd.edu/public/tutorial/Stars.html
Class Temperature Sample star
O 33,000 K or more Zeta Ophiuchi
B 10,500–30,000 K Rigel
A 7,500–10,000 K Altair
F 6,000–7,200 K Procyon A
G 5,500–6,000 K Sun
K 4,000–5,250 K Epsilon Indi
M 2,600–3,850 K Proxima Centauri
Surface Temperature of Stars
Why Study Thermodynamics? Thermal Radiation from Space
Crab NebulaT determines the “colour”.
Radiation energy density
Planck distribution law
T1∝max
infraredUV-Vis.
Spectral Distribution of Thermal Radiation
Effective temperature of the Sun is 5780 K UV-visible radiation.
Power output:
8.1 Watts per kg of engine
Efficiency, = 0.18 (or 18%)
= Eelec/Qin
Eelec = Electric energy out
Qin = net heat energy in
Thermo-Acoustic Engine
Backhaus et al., Applied Physics Letters (2004) 85, p.1085
Compressed helium is cycled between heat exchangers (expanded and cooled), and the movement of the gas generates sound waves.
The sound waves drive a piston, which moves a coiled copper wire through a magnetic field produced by a permanent magnet.
Electric current flows to power the spacecraft.
Why Study Thermodynamics? Efficiency of New Types of Engines
Thermodynamics Provides Equations to Describe Properties of Matter
Properties are inter-related:
• Mechanical (elastic modulus and compressibility)
• Thermo-mechanical (expansivity)
• Flow (viscosity)
• Thermal (heat capacity)
What Happens when Thermodynamics Goes Wrong?
A failed O-ring allowed the escape of H2 gas. The result was an explosion = sudden release of heat
Challenger Space Shuttle Disaster
http://www.ssqq.com/archive/disasters.htm
Columbia Space Shuttle Disaster
Damage to the wing caused over-heating on re-entry into the atmosphere
http://jcwinnie.biz/wordpress/?p=2235http://www.dailymail.co.uk/sciencetech/article-483191/Arctic-ice-cap-melts-smallest-size.html
Greenhouse Effect: A Problem of Thermodynamics
Earth can be treated as a thermodynamic system.
http://en.wikipedia.org/wiki/File:Atmosfaerisk_spredning.gif
Most Intense Thermal Radiance from Earth
Water and Carbon Dioxide Block Thermal Radiation from Earth
Wavelength (m)Thermal radiation
transmitted through
atmosphere to Earth from Sun
Thermal radiation from colder Earth
transmitted through
atmosphere
en.wikipedia.org/wiki/User:Dragons_flight/Images
Source of Nano-Scale Work: Brownian Motion
Random movement of sub-mm particles caused by asymmetric collisions (and momentum transfer) with surrounding molecules.
Can this random movement of particles be “harnessed” to do useful work?