Energy Transfer

1
Energy Transfer

• Conduction, Convection, Radiation
• Global Warming

2
Thermal Conduction

• Materials in direct contact
• Vibrational energy transferred by atoms and free
  electrons
• Metals are good thermal conductors
• Gases are poor thermal conductors
• Rate of energy transfer depends on material

L
Fig. 11.5, p. 366
3
Home Insulation

• In U.S. units are BTUs, feet, ?F, hours
• Compound slabs use R values
• Thin layer of stagnant air at surfaces also
  insulates
• Rate of heat transfer given by

4
Convection

• Transfer of energy by movement of substance
• Natural convection movement from density
  differences
• Forced convection movement by fan or pump

Fig. 11.10, p. 371
5
Radiation

• Electromagnetic waves from thermal vibration of
  molecules carry energy
• Characterized by
• objects emissivity, e
• Stefan-Boltzmann constant, ?
• Surface area, A
• Can also absorb radiation

6
Global Warming and Greenhouse Effect

• Some gases transmit visible light, reflect
  infrared light (like glass of greenhouse)
• CO2, CH4, N2O, SO2
• Leads to stable surface temperature (properly
  called the atmospheric effect)
• Too little ? large changes in temp. (Mars)
• Too much ? constant high temp. (Venus)

Seeds, Foundations of Astronomy, p. 490
7
Four predictions of Earths CO2 History
Predictions based on marine sediments (1)
deuterium, dust, deep ocean carbonate
dissolution, calculated insolation (2)
insolation only model of ice formation (3) and
deuterium levels (4)
Wolff, E., et al. (2005), Modeling past
atmospheric CO2 results of a challenge, EOS
86(38), pp. 341, 345
8
CO2 Measured from ice core samples from
Antarctica
Minima are glacial periods maxima are
interglacial periods
Wolff, E., et al. (2005), Modeling past
atmospheric CO2 results of a challenge, EOS
86(38), pp. 341, 345
9
CO2 measured at Mauna Loa Observatory along with
fossil fuel emissions
Deforestation
Graedel, T.E. and P.J. Crutzen (1993),
Atmospheric Change An Earth System Perspective,
p. 255, W.H. Freeman and Company, New York.
10
CO2 measured at Mauna Loa Observatory
Fig. 11.16, p.376