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.

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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?

Sizes of rotors: between 4-10 nm thick and about 5-12 nm across.

Membrane

Hot gas side

Cold gas side

M. van den Broek and C. Van den Broeck, Physical Review Letters (2008) 100, 130601

Heat flow

Source of Nano-Scale Work: Brownian Motion