What is Thermodynamics?

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– physical movement, e.g. lifting or pushing against friction. Electrical– 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 Heat Burning wood, oil, gas and coal http://www.starlight-news.co.uk/StarlightSolarSystemTheSun.html Heat produced in nuclear fusion reactions within the Sun. Release of potential energy held in chemical bonds http://www.dailymail.co.uk/news/article-1043161/Anti-terror-patrols-secretly-stepped-power-stations.html Controlled nuclear reactions in power stations 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! http://www.stovesonline.co.uk/wood-is-best.html

3. 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

4. The Challenge of Finding Alternative Sources of Energy (Heat or Work) http://www.nearfield.com/~dan/sports/bike/river/coyote/index.htm • Wind is an alternative source of work – but what is the energy source of wind? • Similarly, what is the source of wave energy? • The source of tidal energy can be traced back to gravitational forces.

5. 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/

6. 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.

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

8. 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.

9. 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

10. 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

11. 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.

12. 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

13. 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

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. 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)

16. 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?

17. New Directions: Brownian Motor 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