topic 8: energy, power and climate change nina. 8.1 energy degradation and power generation...
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Topic 8: Energy, Power and Climate Change
Nina
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8.1 Energy degradation and power generation
• Continuous conversion of energy requires a cyclical process
• Degraded energy: transferred to the surroundings and no longer available
• Sankey diagrams• Basic idea of a power station – rotating coils in
magnetic fields
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Sankey diagrams
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8.2 World energy sources
Oil37%
Coal25%
Gas24%
Nuclear6%
Biomass4%
Hydroelectric3%
Other1%
Percentage use
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Energy density
• Energy density (J kg-1) =(energy released from fuel [Joules])/(mass of fuel used [kg]) (not given in DB)• Discuss how this influences the choice of fuel
• Also know all but a few sources of energy originate in the sun somehow
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Efficiency of fossil fuels
Coal PS Oil PS Gas PS
Maximum Efficiency 0.42 0.45 0.52
5%
15%
25%
35%
45%
55%
Maximum Efficiency
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Nuclear power
• You know the general idea• Fuel enrichment: increasing the proportion of
U-235• Fissionable: can undergo nuclear fission• Fissile: fissionable by low KE neutrons• Moderator (eg water): slows neutrons down• Control rod (eg boron): absorbs neutrons
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Nuclear power (2)
• Know that U-235 fission results in neutrons that can be captured by U-238, which decays into Pu-239 which can then be used as fuel in other reactors
• Know general risks/ethical issues (controlled power station vs chain reaction/bomb)
• Know why we can’t (yet) do nuclear fusion
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Solar power
• Photovoltaic cell (PV): produces electrical energy
• Solar panel: produces thermal energy
• Know of seasonal/regional variations in solar power (further from the equator, less intense power)
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Hydroelectric power
• GPE -> KE (water) ->KE (turbines) -> electrical E
• Lake/dams version (“water storage in lakes”)• Tidal version (“tidal water storage”)• Pumping version (“pump storage”)• Know the three different schemes
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Wind power
• Know basic features (nacelle with generator, rotor blades)
• Power delivered= ½ A v𝜌 3
• A = area swept by blades (ᴨr2)• 𝜌 = density of air• v = wind velocity
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Wave power
• Oscillating water column (OSW)
• Power = ½ A2 g v𝜌• A = wave amplitude• 𝜌 = water density• g = gravity• v = wave velocity
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Greenhouse effect
• Inverse square law: I = power/A• I: Intensity • Power of source• Area of sphere around source (4ᴨr2)
• Albedo: proportion of energy reflected compared to the total energy received (equation given in data book). Know relative snow/ocean albedo
• Average earth albedo: 30%
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Greenhouse gases
• Methane, water vapour, carbon dioxide, nitrous oxide (natural and man-made origins)
• Resonance between gases’ natural frequency of oscillation and infrared emitted by Earth
• Gases ‘trap’ infrared and reemit it in all directions (among which back to Earth)
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Black body radiation
• Absorbs all radiation and reflects none: black when cold.
• When hot emits radiation at all wavelengths. ‘Perfect’ emitter.
• Power emitted by a black body = σAT4
• σ: Stefan-Boltzmann constant (5.67 x10-8 Wm-2K-
4)• A: surface area of the emitter• T: temperature of the emitter (K)
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Emissivity (e)
• How well a surface emits radiation• Between 0 and 1. Perfect emitter has
emissivity of 1• -> power emitted by any body = eσAT4
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Surface heat capacity
• Measurement of how much energy is required to heat up 1 m2 of a surface by 1°C
• Cs= Q/AΔT
• Cs: surface heat capacity• Q: energy necessary• A: land area• ΔT: temperature difference
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Global warming
• Change of a planet’s temperature over a period of time:
• ΔT= [(Iin – Iout) Δt]/Cs
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Global warming (2)
• International ice core research• Coefficient of volume expansion• International efforts:– Intergovernmental Panel on Climate Change (IPCC)– Kyoto Protocol– Asia-Pacific Partnership on Clean Development
and Climate (APPCDC)
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In conclusion: READ THE SYLLABUS
http://gradegorilla.com/IBclimate/climate1.php