energy transfer on earth

1. 8.2 Thermal Energy transfer

2. There are three forms of heat transfer:
Conduction
Convection
Radiation
2Forms of energy transfer

3. 3
http://www1.teachertube.com/viewVideo.php?video_id=159713

4. Explaining Conduction 4
What happens if we heat part of a metal rod?
The particles in that part of the rod vibrate more.
The particles pass on the vibration to other particles along the
rod.
The colder area warms up.

5. Convection
The transfer of heat in a liquid or gas, by the
movement of particles, when less dense
liquids rise and more dense liquids flow in to
take its place.
This movement is called
convection current
5

6. What happens to the particles in a liquid or a gas
when you heat them?
The particles spread out and become
less dense.
This effects fluid movement.
A liquid or gas.
Heating Fluids 6

7. Why is the freezer compartment in a fridge at
the top?
Freezer
compartment
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
It is warmer at
the bottom, so
this warmer air
rises and a
convection
current is set
up.
7

8. Radiation
A transfer of heat from a hot object through space
or air to a cold object.
This process does not depend on particles to
transmit heat.
Heat energy is transferred as radiation even when
no particles are present.
Emissivity is the property that allows us to
compare radiators – find out about the emissivity
of snow and coal.
8

9. Apply
1. Why is there a sea breeze?
2. How do air conditioning units work?
3. Compare ceramic and metal pans
4. How did the mid-atlantic ridge form?
5. Are black cans better heaters?

10. Solar Radiation
The Sun, with a surface temperature of nearly
6,000 degrees K, emits radiation in the ultra-
violet(8%), visible(43%) and infra-red (49%)
regions of the electro-magnetic spectrum.
The Earth intercepts about 0.5 billionth of the
Sun’s total radiation
About half of the solar radiation reaching the
lower atmosphere actually warms the Earth’s
surface (15 degrees C average).
The remainder of the radiation is either
reflected by clouds and oceans, or absorbed by gases
in the atmosphere.

11. Solar Radiation
The solar constant is defined as the amount of solar
energy per second that falls on an area of 1m2 of the
upper atmosphere perpendicular to the suns’ rays
Another name for the solar constant is the sun’s
energy flux
The solar constant has a value of 1.35 kWm-2
The solar constant varies due to the elliptical orbit
of the Earth and age of Sun.
The total solar radiation reaching the top of the
atmosphere is about 1.7 x 10 17 W which is 170 Wm-2
averaged over a day and night

12. Solar Radiation
 The total solar radiation is 170 Wm-2
averaged over a day and night how much
energy does 1km2 of the Earth receive in
a day?

13. Black body radiation
A black body is an object that absorbs all
electromagnetic radiation that falls on it. No
electromagnetic radiation passes through it and none
is reflected. Because no light (visible
electromagnetic radiation) is reflected or
transmitted, the object appears black when it is
cold.
If the black body is hot, these properties make it an
ideal source of thermal radiation.

14. Black body radiation
From the measured values for the Sun,
Ts=5778K
Rs=6.96 * 108m
D=1.496*1011
albedo=0.367
we'll find the effective temperature of the Earth to
be
Te=248.53K
This is the black body temperature that would cause
the same amount of energy emission, as measured
from space, while the surface temperature is higher
due to the greenhouse effect.

15. Black body radiation
 Graph of light emission at different
Temperatures

16. Black body radiation
 Stefan Boltzmann
The energy radiated by a blackbody
radiator per second per unit
area is proportional to the
fourth power of the absolute
temperature and is given by

17. Black body radiation
 Emissivity
The emissivity of a material (usually written ε or e) is the ratio
of energy radiated by a particular material to energy
radiated by a black body at the same temperature.
It is a measure of a material's ability to radiate absorbed
energy. A true black body would have an while any real
object would have . Emissivity does not have units.
In general, the duller and blacker a material is, the closer its
emissivity is to 1. The more reflective a material is, the
lower its emissivity

18. Black body radiation
 Surface heat capacity
Also known simply as specific heat, is the measure of the heat
energy required to increase the temperature of a unit
quantity of a substance by a certain temperature interval.
More heat energy is required to increase the temperature of a
substance with high specific heat capacity than one with low
specific heat capacity.
Molecules have internal structure because they are composed of atoms
that have different ways of moving within molecules. Kinetic energy
stored in these internal degrees of freedom contributes to a
substance’s specific heat capacity and not to its temperature.

19. Albedo
Albedo at a surface is the ratio
between the incoming radiation and
the amount reflected …expressed as a
% or coefficient
Recall solar radiation is mainly in the
visible and infrared regions (we call
the incoming short wave infrared
insolation)

20. Albedo

21. Albedo
Incoming radiation will be INSOLATED, REFLECTED
and RETRANSMITTED in various ways.
 30% reflected
 51% absorbed at surface
(23% of which is used in the water cycle)
 19% absorbed in atmosphere
Albedo is affected by seasons, day, latitude.
Global annual mean albedo is 0.3

22. Albedo
 The proportion of absorbed,
emitted, and reflected incoming
solar radiation steers the
Earth's climate system causing
fluctuations in temperature,
winds, ocean currents, and
precipitation.
 The climate system remains in
equilibrium as long as the
amount of absorbed solar
radiation is in balance with the
amount of terrestrial radiation
emitted back to space.

23. Carbon dioxide emissions
 Carbon dioxide is one of
the main contributors to
greenhouse effect. It
contributes 9-26% to the
greenhouse effect.
 The image shows the
increasing density of
carbon dioxide in the
atmosphere contributed
by human activity

24. Carbon dioxide emissions
The seven sources of CO2 from fossil fuel combustion
are (with percentage contributions for 2000–2004):
 Solid fuels (e.g. coal): 35%
 Liquid fuels (e.g. gasoline): 36%
 Gaseous fuels (e.g. natural gas): 20%
 Flaring gas industrially and at wells: <1%
 Cement production: 3%
 Non-fuel hydrocarbons: <1%
 The "international bunkers" of shipping and air
transport not included in national inventories: 4%

25. IR spectra of greenhouse gases

26. Greenhouse gases absorb infra-red
radiation strongly in the bands with
wavelengths between 12,500 – 17,000 nm
and 4,500 – 7,000 nm. In between these
two bands more than 70% of the radiation
is emitted from the Earth’s surface
escapes through the atmosphere.
When infra-red radiation is absorbed the
bonds in the molecules to vibrate, where
the distances between bonded atoms
increases and decreases in a rhythmical
manner as if connected by springs.
It is possible for resonance to occur if the
vibration frequency matches the molecules
natural frequency (for greenhouse gases
their natural f is in the infrared region)

27. IR absorption of
greenhouse gases
 Polyatomic molecules have more numerous
vibrations, at least some of which are
‘infrared-active’. The main infrared
absorbers in the atmosphere are water and
carbon dioxide. At the long wavelengths of
terrestrials radiation, the bending
vibrations of these molecules are chiefly
responsible for absorption.

28. What is the Greenhouse Effect?
The greenhouse effect is a natural warming
process. Put simply natural greenhouse gases
absorb outgoing long wave radiation and re-radiate
some of it back to Earth
The absorbed energy warms the earth's surface
which then emits heat energy back toward space as
longwave (infra-red) radiation. This outgoing infra-
red radiation is partially absorbed by greenhouse
gases which then radiate the energy in all directions,
warming the earth's surface and lower atmosphere.
Without these greenhouse gases the earth's
average surface temperature would be about 33
degrees Celsius cooler, that is the same temperature
as the Moon.

29. http://interactive.usask.ca/ski/media/drawings/agriculture/greenhouse.jpg

30. Greenhouse Gases
The main natural greenhouse gases are water vapour,
carbon dioxide, methane, and nitrous oxide.
All except water vapour have increased in
concentrations in the atmosphere since the 1950s.
Other greenhouse gases include ozone and
halocarbons.
Most of the greenhouse effect is due to water, with
carbon dioxide contributing about 1 degree to the
warming effect.
Only polar molecules can absorb infra-red radiation
so the most common gases in the atmosphere, oxygen
(O2) and nitrogen (N2), do not contribute to the
Greenhouse Effect.

31. Source of Gases
Greenhouse
Gas
Main
Source
Human
Activity
Carbon
dioxide
Combustion of
fossil fuels
Transport, power
and energy
production, burning
of rainforests.
Methane Anaerobic
breakdown of
plant matter
Rice growing, cattle
and sheep farming
Nitrous
Oxide
Denitrificatio
n of nitrates
by microbes
Use of nitrogenous
fertilizers in
agriculture

34. Energy balance models
There are four main categories of model:
 EBM – use spreadsheets to study
incoming/outgoing global radiation, using different
latitudes from equator to pole
 RCM – simulate atmospheric environments, only
radiation balance and convection heat transfer
 STM – combination of energy balance and
radiative-convective models
 GCM – 3D general circulation model simulating
global climate

35. Global Warming?
 The natural greenhouse effect has been
significantly intensified by human activities that
increase the concentrations of greenhouse gases
(mostly carbon dioxide, methane and nitrous
oxide) in the atmosphere.
 These greenhouse gases increase the retention of
heat in the troposphere and contribute toward
(cause) global warming or, more accurately, climate
change.
(Note: Not all parts of the Earth may experience
increases in temperatures e.g. UK temperatures
may decrease.)

36. Enhanced Greenhouse Effect

37. Major Impacts
 A Rise in Temperature varying with latitude & season, with
longer summers and shorter winters.
 Change in Climate with small temperature changes resulting
in large impacts on climate.
 Higher Evaporation Rates and increased, but uneven, global
rainfall (drier South Australia, wetter Northern
Territory).
 Change in Natural Ecosystems with increasing extinction of
native flora and fauna.
 Increase in Photosynthesis with domination of weed species.
 Rises in Sea Level due to warming and expansion of oceans
and melting of land-based ice.
 Weather Extremes during the transition to an enhanced
greenhouse Earth.

38. Major Impacts
What evidence do we have for global warming?
 Ice core data
 Tree ring data
 Sedimentary records
 Glacial melting