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What is Thermodynamics?

The study of energy in the forms of heat and work and the exchange between the two. Work. Heat. http://www.hybridmile.com/files/2008/10/engine--1.JPG. http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htm.

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What is Thermodynamics?

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  1. The study of energy in the forms of heat and work and the exchange between the two. Work Heat http://www.hybridmile.com/files/2008/10/engine--1.JPG http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htm Mechanical work– physical movement, e.g. lifting or pushing against friction. Electrical work– flow of current What is Thermodynamics? • 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

  2. 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. Combustion of wood, oil, gas and coal http://www.dailymail.co.uk/news/article-1043161/Anti-terror-patrols-secretly-stepped-power-stations.html http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htm

  3. Forms of Solar Energy FormExplanation and Use Solar 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 From P.A. Tipler, Physics, Ch. 18

  4. 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)?

  5. Power radiated per unit area at RSE: Stefan-Boltzmann equation tells us the power (energy per unit of time: W = J/s) radiated per unit area (m2) of its surface: Power reaching the Earth: TSun = 5800 K RSun = 7 x 108 m Luminosity: L =PRA= 3.8 x 1026 W About 70% of radiation reaches Earth: Energy is emitted in all directions 4.9 x 1017 W: Plenty to meet human needs! Energy Radiated by the Sun Earth RSun RE=6378 km RSE = 1.5 x 1011 m Sun

  6. Why Study Thermodynamics: Are perpetual motion machines possible? Three Laws of Thermodynamics (plus Zeroth Law) http://www.todayinsci.com/Books/MechApp/chap23/page28.htm 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/

  7. Thermal expansion of girders was restricted by frictional forces. They could not expand lengthwise, so they buckled! Why Study Thermodynamics? Thermal Expansion Joints in bridges are used to enable thermal expansion. (Pressure, volume and temperature are interrelated in solids.)

  8. Why Study Thermodynamics? Understanding Gases Meteorology: high and low pressure http://www.jamie.aarontastic.com/Low%20Pressure%20Example.JPG Measuring Lung Capacity Ideal Gas: Pressure, Volume and Temperature relationships http://www.heart-watch-blog.com/images/blogs/7-2007/lung-capacity-7810.jpg

  9. Why Study Thermodynamics? Heat Dissipation http://communication.howstuffworks.com/laptop.htm/printable 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.)

  10. Why Study Thermodynamics? Thermal Radiation from Space Surface Temperature of Stars Crab Nebula T determines the “colour”. http://en.wikipedia.org/wiki/File:Crab_Nebula.jpg http://cass.ucsd.edu/public/tutorial/Stars.html

  11. Spectral Distribution of Thermal Radiation Radiation energy density Effective temperature of the Sun is 5780 K UV-visible radiation. infrared UV-Vis. Planck distribution law

  12. Why Study Thermodynamics? Efficiency of New Types of Engines 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. Thermo-Acoustic Engine Efficiency, h= 0.18 (or 18%) h = Eelec/Qin Eelec= Electric energy out Qin = net heat energy in Power output: 8.1 Watts per kg of engine Backhaus et al., Applied Physics Letters (2004) 85, p.1085

  13. 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)

  14. A failed O-ring allowed the escape of H2 gas. The result was an explosion = sudden release of heat http://www.ssqq.com/archive/disasters.htm Challenger Space Shuttle Disaster What Happens when Thermodynamics Goes Wrong? Damage to the wing caused over-heating on re-entry into the atmosphere Columbia Space Shuttle Disaster

  15. Greenhouse Effect: A Problem of Thermodynamics http://jcwinnie.biz/wordpress/?p=2235 http://www.dailymail.co.uk/sciencetech/article-483191/Arctic-ice-cap-melts-smallest-size.html Earth can be treated as a thermodynamic system.

  16. Water and Carbon Dioxide Block Thermal Radiation from Earth Wavelength (mm) 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 Most Intense Thermal Radiance from Earth http://en.wikipedia.org/wiki/File:Atmosfaerisk_spredning.gif

  17. 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?

  18. Source of Nano-Scale Work: Brownian Motion Sizes of rotors: between 4-10 nm thick and about 5-12 nm across. Hot gas side Heat flow Membrane Cold gas side M. van den Broek and C. Van den Broeck, Physical Review Letters (2008) 100, 130601

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