What is Thermodynamics? Mechanical work – physical movement, e.g. lifting or pushing against friction. Electrical work – flow of current 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. 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 FormExplanation and Use Solar radiationDirect 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) PhotosynthesisSolar energy is converted to chemical energy in plants and fossil fuels. Solids, liquids and gases are used in combustion. Wind powerHeating 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 powerSun drives water cycle (evaporation, rain) which is converted to mechanical or electrical energy (usually using gravity). news.co.uk/StarlightSolarSystem TheSun.html

Does enough heat come from the Sun to meet human needs? 1 tonne of crude oil (7 barrels) yields 4.2 x10 10 J of heat. But humans consume about 1.3x10 13 W of energy – equivalent to 300 tonnes of crude oil per sec! 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 (m 2 ) of its surface: Sun Earth R SE = 1.5 x m T Sun = 5800 K R Sun = 7 x 10 8 m Luminosity: L =P R A= 3.8 x W Energy is emitted in all directions Power radiated per unit area at R SE : R E =6378 km Power reaching the Earth: About 70% of radiation reaches Earth: 4.9 x W: Plenty to meet human needs! R Sun

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 Meteorology: high and low pressure Measuring Lung Capacity Ideal Gas : Pressure, Volume and Temperature relationships

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.)

ClassTemperatureSample star O33,000 K or moreZeta Ophiuchi B10,500–30,000 KRigel A7,500–10,000 KAltair F6,000–7,200 KProcyon A G5,500–6,000 KSun K4,000–5,250 KEpsilon Indi M2,600–3,850 KProxima Centauri Surface Temperature of Stars Why Study Thermodynamics? Thermal Radiation from Space Crab Nebula T determines the “colour”.

Radiation energy density Planck distribution law infrared UV-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%)  = E elec /Q in E elec = Electric energy out Q in = 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 H 2 gas. The result was an explosion = sudden release of heat Challenger Space Shuttle Disaster Columbia Space Shuttle Disaster Damage to the wing caused over-heating on re-entry into the atmosphere

Greenhouse Effect: A Problem of Thermodynamics Earth can be treated as a thermodynamic system.

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, Heat flow Source of Nano-Scale Work: Brownian Motion