Understanding Heat Transfer: Conduction, Convection and Radiation
Understanding Heat Transfer, Conduction, Convection And
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Transcript of Understanding Heat Transfer, Conduction, Convection And
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Understanding Heat Transfer,
Conduction, Convection and
Radiation
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Heat Transfer
Heat always moves from a warmer place to a
cooler place.
Hot objects in a cooler room will cool to room
temperature.
Cold objects in a warmer room will heat up to
room temperature.
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Conduction
When you heat a metal strip at one end, the heat
travels to the other end.
As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. We call this CONDUCTION.
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Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metalconducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
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What is an insulator???
A thermal insulatoris a material that conducts heatpoorly.
Heat flows very slowly through the plastic so that thetemperature of your hand does not rise very much.
Liquids and gases are also extremely poor conductors.
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Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out andbecome less dense.
This affects fluid movement.
Remember, fluid = liquid OR gas
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Fluid movementCooler, more dense, fluidssink through warmer, lessdense fluids.
In effect, warmer liquids and gases riseupwards.
Cooler liquids and gases sink downwards.
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Why is it windy at the seaside?
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Much of the Earths climate is regulated by giant convection
currents in the ocean.
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Cold air sinks
Where is thefreezercompartment
put in a fridge?
Freezercompartment
It is put at the top,because cool air
sinks, so it cools thefood on the way
down.
It is warmer at
the bottom, sothis warmer air
rises and aconvection
current is set up.
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The third method of heat transfer
How does heat energy get
from the Sun to the Earth?There are no particles betweenthe Sun and the Earth so it
CANNOT travel by conduction or
by convection.
?RADIATION
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Radiationis heat transfer
by electromagnetic waves.
Thermal radiationis
electromagnetic waves
(including light) producedby objects because of their
temperature.
The higher the
temperature of an object,
the more thermal radiation
it gives off.
Radiation
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We do not see thethermal radiation
because it occurs atinfrared wavelengthsinvisible to the humaneye.
Objects glow differentcolors at differenttemperatures.
ALL objects emit SOME
form of radiant energy. ALL objects also
ABSORB some amountof radiant energy.
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The Greenhouse Effect
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Earths Atmospheric Gases
Nitrogen (N2)
Oxygen (O2)
Water (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Non-Greenhouse
Gases
99%
Greenhouse
Gases
1%
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Sun
Earths Temperature
Solar
Energy
RadiationCooling
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Sun
Earths Temperature
Solar
EnergyRadiationCooling
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Sun
Earths Temperature
Solar
Energy
Radiation
Cooling
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To change phases of matter,
you either gain or lose
thermal energy (you
transfer some heat)!
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Enthalpy of Fusion
Enthalpy of Vaporization
