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Global Warming: or Thermal Management on the Big Spaceship Lecture #22 Space concepts The Big Spaceship Agenda Planetary temperatures Venus Earth Is Global Warming Real? What is driving it? A Simple Model Solutions Blackbody Radiation Curve Black Body Radiation Curve

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Presentation Transcript
agenda
Agenda
  • Planetary temperatures
  • Venus
  • Earth
  • Is Global Warming Real?
  • What is driving it?
  • A Simple Model
  • Solutions
slide6

Blackbody radiation

  • If a body absorbs and radiates EM radiation perfectly, it is called a “blackbody”
  • It then radiates power by the Stefan Boltzman Law W/m2= T4
    • =emissivity, 1 for a black body ,  >1 for real surfaces
    • =5.76x 10 –8 Wm –2 K-4
    • ( Stefan-Boltzmann constant)
slide8

Space Thermal Radiation problems

  • Spacecraft receive and radiate heat by blackbody radiation
  • They receive radiation in the visible
  • ~ .5-micron because the sun is hotter than they are ( 10,000K)
  • They radiate at much lower temperature ~300K peak radiation ~ 10microns
kirkhoff s law
Kirkhoff’s Law
  • Energy balance Poynting’s theorem
radiant equilbrium
Radiant equilbrium

Planetary radiance

Sunlight

Infrared

Energy arrives at visible frequencies and is radiated at infrared frequencies

Gaussian surface

slide12

Heat Transport

Thermal Conduction:

Heat transport from hot to cold

Heat flows downhill

thermal conduction
Thermal Conduction

Heat flows downhill

slide14

Molecular Mean Free Path

Mean free path =

A mean free path is the scale size on which molecules mix and transport energy, momentum in a gas.

slide15

Molecular Thermal Transport

Downward flux of enthalpy h= cpT

Net flux

Upward flux of enthalpy h= cpT

slide16

Photon Mean Free Path

photon

molecule

Photon Mean free path =p

A photon mean free path is the scale size on which photons of a given wavelength are absorbed and reradiated and transport energy in a gas.

slide17

Radiation Thermal Transport

Downward flux of energy E= cp (T’)T’

p

Net flux

Upward flux of enthalpy E= cp(T)T

thermal photon diffusivity
Thermal Photon Diffusivity

Diffusivity is lowered by increased CO2!!

slide20

about 5×10^-22 m^2 per molecule =5 x 10-18cm2

3 x1019 cm3 molecles x 300 x10-6 co2 = 9x10 15 cm3

1/(sig n) = 1/(5 x 10 -18 cm2 x 9 x10 15 cm3 ) =1 /(.45 x 10-1) = 20 cm mean free path at 15 microns

slide23

Reflected Sunlight

Emitted Thermal

slide24

Thermal Emission

CO2 emission and absorption band

global warming and causes
Global Warming and Causes
  • Global warming appears to be a fact, temperatures are rising –especially since 1980
  • Solar radiance for the last decade appears flat or decreasing
  • Volcanic activity , indicating geothermal heating, appears flat or decreasing
  • Green House gases are rising –appearing to correlate with warming
conclusions
Conclusions
  • Global warming appears to be a reality
  • Global warming appears principally driven by decreased infrared diffusivity in the atmosphere due to increased greenhouse gases-other explanations do not appear viable
  • Global warming, if unchecked, could have very negative consequences for the human race
solutions
Solutions
  • Humanity must shift from fossil fuels to nuclear power and other non-greenhouse producing forms of energy.
  • France and Japan have converted to 80% nuclear Fission – it is both possible and practical
  • Fusion power , cleaner and safer than Fission , can replace all fossil fuels